Tsunami devastates Indian Ocean coast

Tsunami devastates Indian Ocean coast


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A powerful earthquake off the coast of Sumatra, Indonesia, on December 26, 2004 sets off a tsunami that wreaks death and devastation across the Indian Ocean coastline. The quake was the second strongest ever recorded and the estimated 230,000 dead made this disaster one of the 10 worst of all time.

It was 7:58 a.m. when the tremendous quake struck beneath the Indian Ocean 160 miles west of Sumatra. Not only did it register at approximately a 9.3 magnitude (only the 1960 Chile earthquake measured higher at 9.5, though there may have been stronger tremors prior to the invention of seismographic equipment) and last nearly 10 minutes, the quake moved a full 750 miles of underwater fault line earth up to 40 feet. The movement of the earth—there is evidence that huge boulders weighing thousands of tons were pushed several miles along the ocean floor—caused a massive displacement of water. It is estimated that the resulting tsunami had two times the energy of all the bombs used during World War II.

READ MORE: The Deadliest Tsunami in Recorded History

Within 15 minutes, tsunami waves were crashing the coast of Sumatra. At the north end of the island was a heavily populated region known as Aceh. There, waves reached 80 feet high over large stretches of the coast and up to 100 feet in some places. Entire communities were simply swept away by the water in a matter of minutes. The death toll in Indonesia is estimated at between 130,000 and 160,000 people, with an additional 500,000 people left homeless. About a third of the victims were children.

The huge waves missed the coast of Indonesia on the north side and went on to Thailand, where between 5,000 and 8,000 people died. The tsunami also moved east across the Indian Ocean. In Sri Lanka, the tsunami came ashore about 90 minutes after the earthquake. Although the waves were not as high as in Aceh, they still brought disaster. Approximately 35,000 people lost their lives and half a million others lost their homes. In addition, about 15,000 people died in India. The killer waves even reached 5,000 miles away in South Africa, where two people perished.

In total, about 190,000 people are confirmed dead with another 40,000 to 45,000 missing and presumed dead. Although billions of dollars of humanitarian aid poured in to the affected region in the aftermath of the disaster—an estimated $7 billion within the first 18 months—some areas continued to suffer from the massive devastation.

One year prior to this earthquake and tsunami, almost to the hour, a 6.6-magnitude quake rocked Bam, Iran, killing 30,000 people.


Tsunami devastates Indian Ocean coast

It was 7:58 a.m. when the tremendous quake struck beneath the Indian Ocean 160 miles west of Sumatra. Not only did it register at approximately a 9.3 magnitude (only the 1960 Chile earthquake measured higher at 9.5, though there may have been stronger tremors prior to the invention of seismographic equipment) and last nearly 10 minutes, the quake moved a full 750 miles of underwater fault line earth up to 40 feet. The movement of the earth–there is evidence that huge boulders weighing thousands of tons were pushed several miles along the ocean floor–caused a massive displacement of water. It is estimated that the resulting tsunami had two times the energy of all the bombs used during World War II.

Within 15 minutes, tsunami waves were crashing the coast of Sumatra. At the north end of the island was a heavily populated region known as Aceh. There, waves reached 80 feet high over large stretches of the coast and up to 100 feet in some places. Entire communities were simply swept away by the water in a matter of minutes. The death toll in Indonesia is estimated at between 130,000 and 160,000 people, with an additional 500,000 people left homeless. About a third of the victims were children.

The huge waves missed the coast of Indonesia on the north side and went on to Thailand, where between 5,000 and 8,000 people died. The tsunami also moved east across the Indian Ocean. In Sri Lanka, the tsunami came ashore about 90 minutes after the earthquake. Although the waves were not as high as in Aceh, they still brought disaster. Approximately 35,000 people lost their lives and half a million others lost their homes. In addition, about 15,000 people died in India. The killer waves even reached 5,000 miles away in South Africa, where two people perished.

In total, about 190,000 people are confirmed dead with another 40,000 to 45,000 missing and presumed dead. Although billions of dollars of humanitarian aid poured in to the affected region in the aftermath of the disaster–an estimated $7 billion within the first 18 months—some areas are still suffering from the massive devastation.

One year prior to this earthquake and tsunami, almost to the hour, a 6.6-magnitude quake rocked Bam, Iran, killing 30,000 people.


Indian Ocean tsunami of 2004

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Indian Ocean tsunami of 2004, tsunami that hit the coasts of several countries of South and Southeast Asia in December 2004. The tsunami and its aftermath were responsible for immense destruction and loss on the rim of the Indian Ocean.

On December 26, 2004, at 7:59 am local time, an undersea earthquake with a magnitude of 9.1 struck off the coast of the Indonesian island of Sumatra. Over the next seven hours, a tsunami—a series of immense ocean waves—triggered by the quake reached out across the Indian Ocean, devastating coastal areas as far away as East Africa. Some locations reported that the waves had reached a height of 30 feet (9 metres) or more when they hit the shoreline.

The tsunami killed at least 225,000 people across a dozen countries, with Indonesia, Sri Lanka, India, Maldives, and Thailand sustaining massive damage. Indonesian officials estimated that the death toll there alone ultimately exceeded 200,000, particularly in northern Sumatra’s Aceh province. Tens of thousands were reported dead or missing in Sri Lanka and India, a large number of them from the Indian Andaman and Nicobar Islands territory. The low-lying island country of Maldives reported more than a hundred casualties and immense economic damage. Several thousand non-Asian tourists vacationing in the region also were reported dead or missing. The lack of food, clean water, and medical treatment—combined with the enormous task faced by relief workers trying to get supplies into some remote areas where roads had been destroyed or where civil war raged—extended the list of casualties. Long-term environmental damage was severe as well, with villages, tourist resorts, farmland, and fishing grounds demolished or inundated with debris, bodies, and plant-killing salt water.


National Tsunami Warning Center (NTWC)


The Palmer Observatory, under the auspices of the Coast and Geodetic Survey, was established in Palmer, Alaska in 1967 as a direct result of the great Alaskan earthquake that occurred in Prince William Sound on March 27, 1964. This earthquake alerted State and Federal officials that a facility was necessary to provide timely and effective tsunami warnings and earthquake information to the coastal areas of Alaska. Congress provided funds in 1965 to construct two new observatories and establish a tsunami warning system in Alaska. The first observatory constructed was at the U.S. Naval Station on Adak Island in the Andreanof Islands in the Central Aleutians. The City of Palmer, in the Matanuska Valley 42 miles northeast of Anchorage, was selected as the site for the primary observatory due to its proximity to bedrock for instrumentation and to communications facilities. Construction of the observatory installations, the task of engineering and assembling the data systems, and the hookup of the extensive telecommunications and data telemetry network was completed in the summer of 1967. With the dedication of the Palmer Observatory on September 2, 1967, the Alaska Regional Tsunami Warning System (ARTWS) became operational.

Originally, the tsunami warning responsibility for Alaska was shared by the three observatories located at Palmer, Adak and Sitka. Sitka, a seismological observatory since 1904, and Fairbanks were the only two seismic stations operating in Alaska in 1964. The responsibilities of Adak and Sitka were limited to issuing a tsunami warning for events occurring within 300 miles of their location. In later years, the responsibility to provide tsunami warning services for Alaska was transferred from the Adak and Sitka observatories to the Palmer Observatory. Sitka and Adak Observatories were eventually closed in the early 1990s, although the seismic instrumentation is still maintained.

In 1973, the Palmer Observatory was transferred to the National Weather Services Alaska Region and changed its name to Alaska Tsunami Warning Center (ATWC). In 1982, its area of responsibility (AOR) was enlarged to include the issuing of tsunami warnings to California, Oregon, Washington, and British Columbia for potential tsunamigenic earthquakes occurring in their coastal areas. In 1996, the responsibility was again expanded to include all Pacific-wide tsunamigenic sources that could affect the California, Oregon, Washington, British Columbia and Alaska coasts, and the name was changed to the West Coast/Alaska Tsunami Warning Center (WCATWC) to reflect those new responsibilities. October 1, 2013 the West Coast and Alaska Tsunami Warning Center became the National Tsunami Warning Center (NTWC)


Tsunami devastates Indian Ocean coast - HISTORY

Tsunamis of the Indian Ocean

Copyright © 2005. All Rights Reserved

Introduction

Although not as frequent as in the Pacific Ocean, tsunamis generated in the Indian Ocean pose a great threat to all the countries of the region. The most vulnerable are: Indonesia, Thailand, India, Shri Lanka, Pakistan, Iran, Malaysia, Myanmar, Maldives, Somalia, Bangladesh, Kenya, Madagaskar, Mauritius, Oman, Reunion Island (France), Seychelles, South Africa, and Australia.

The Great Earthquake of December 26, 2004 off the west coast of Northern Sumatra generated the most devastating tsunami in history. It killed more than 225,000 people with thousands more reported missing and left unprecedented devastation along its path across the Bay of Bengal and the entire Indian Ocean.

Although not as destructive as the 26 December 2004 event was, many more tsunamis have been generated by large earthquakes in subduction zones bordering the Indian Ocean and by smaller magnitude events along the Central Indian and Carlsberg mid-oceanic ridges. The recent historical record shows that major tsunamis occurred in 1524, 1762, 1819, 1847, 1881, 1941, 1945, 1977 and in 2004. Additionally, the 26 August 1883 Ultra Plinian eruption and collapse of the Krakatau (Krakatoa) volcano in the Sunda Strait - between Java and Sumatra - generated the best known and documented tsunami in recorded history. This particular tsunami killed 37,000 people in the islands of Java and Sumatra. There may be additional destructive tsunamis in the Indian Ocean that have not been properly documented. For example villagers of Simeulue Island , off the coast of Sumatra, speak of a destructive tsunami in 1907 that had killed thousands of people.

Seismotectonics of the Indian Ocean Region - Potential Tsunami Generating Sources

The following is only a brief overview of the tectonic setting and interactions that result in tsunamigenic earthquakes in the Indian Ocean.

The India tectonic plate has been drifting and moving in a north/northeast direction, for millions of years colliding with the Eurasian tectonic plate and forming the Himalayan mountains.

USGS graphic showing the migration of the Indian tectonic plate

As a result of such migration and collision with both the Australian and the Eurasian tectonic plates and subplates, the Indian plate's eastern boundary is a diffuse zone of seismicity and deformation, characterized by extensive faulting and numerous earthquakes that can generate destructive tsunamis.

To the west, similar interaction of the India plate with the Arabian and Iranian microplates of the Eurasian block, has created an active subduction zone along the Makran coast of Pakistan. A major fault in this region has produced several tsunamigenic earthquakes recently and in the distant geologic past. This major fault is of the same character as the West Coast fault along the coast of Maharashtra, India - which is also a region that can produce tsunamigenic earthquakes. Further south on the western side the Indian tectonic plate is bounded by the Central Indian and Carlsberg mid-ocean ridges, a region of shallow seismicity.

To the east, subduction of the Indo-Australian Plates beneath the Burma and Sunda Plates has formed the extensive Sunda Trench - a very active sismic region where large earthquakes are frequent. The volcanoes of Krakatau, Tambora and Toba , well known for their violent eruptions, are byproducts of such tectonic interactions. A divergent boundary separates the Burma plate from the Sunda plate in the north. The Burma plate encompasses the northwest portion of the island of Sumatra as well as the Andaman and the Nicobar Islands, which separate the Andaman Sea from the Indian Ocean.

Destructive tsunamis can originate from earthquakes that occur along these principal tectonic sources . The major tectonic feature in the region is the Sunda Arc that extends approximately 5,600 km between the Andaman Islands in the northwest and the Banda Arc in the east. The Sunda Arc consists of three primary segments the Sumatra segment, the Sunda Strait Segment and the Java Segment. These locations represent the area of greatest seismic exposure, with maximum earthquake magnitudes of up to 7.75 or even more on the Richter scale - as the 26 December 2004 proved.

According to recent studies reported in the Earth and Planetary Science Letters (vol 133), the Indo-Australian plate does not appear to be coherent. The two plates appear to have separated many million years ago. Also, it appears that the Australian plate is rotating in a counterclockwise direction, putting stress on the southern segment of the India plate.

The movement of the Australian plate can generate earthquakes along the southern end of western Sumatra, along the Sunda Strait segment of the great tectonic arc, or further east along the Java segment, off the Lesser Sunda Islands or at Flores Island of Indonesia. Active tectonic interaction in this eastern section of the great arc has produced destructive earthquakes and tsunamis in the distant past and as recently as 1977, 1992 and 1994.

Smaller magnitude earthquakes along the mid-Indian ocean ridge have the potential of generating smaller local tsunamis. Finally, deltaic sediment accumulations of major rivers have also the potential of generating tsunamis. Such landslides can be triggered even by earthquakes of lesser magnitude.

British Geological Survey graphic of the seismicity of Southern Asia of the Carlsberg Midoceanic Ridge and of the southern portion of the Arabian Peninsula and the Red Sea.

Recent Tsunamis of the Indian Ocean

(partial listing - being updated)

Although not as frequent as in the Pacifc, destructive earthquakes and tsunamis have occurred in the Indian Ocean troughout geologic history and in recent times. Most of these events have not been adequately documented, leading to the erroneous impression by many that tsunamis do not occur often enough to present a risk that requires the establishment of a Regional Tsunami Warning System in the Indian Ocean.

However, the destruction and high death toll caused by the 26 December 2004 tsunami disaster indicates how underestimated this hazard has been - especially by the countries that were so adversely afflicted. Although not frequent , major tsunamis have occurred in the Indian Ocean. At least eight of these were major events, which have been documented - but some not adequtely . Of course, one of these was the well-known catastrophic tsunami generated from the ultra Plinian eruption of Krakatau on 26 August, 1883. The tsunami waves reached over 30 meters and killed about 37,000 people in Java and Sumatra.

Other major tsunamis occurred in 1524, 1762, 1819, 1847, 1881, 1941, 1945 and in 1977. Less destructive tsunamis have also occurred more recently. The following is a summary of only a few of the historical Indian Ocean tsunamis (Further information on Indian Ocean earthquakes and tsunamis will be provided with subsequent updates).

The Earthquake and Tsunami of 31 Dec 1881 in the Andaman Sea

A major earthquake (with estimated Richter magnitude of 7.9 ) in the vicinity of Car Nicobar island, in the Andaman Sea, generated a destructive tsunami which must affected the entire Andaman and Nicobar island group, and quite possibly the entire Bay of Bengal region. Waves of 1 meter height were recorded by a tide gauge station at Chennai, on the East coast of India. Additional documentation will be provided with a later update

The Earthquake and Tsunami of 26 June 1941 in the Andaman Sea

On June 26, 1941 (11:52:03 UTC), a devastating earthquake (Mw 7.7 , Mb 8.0, Ms 7.7) occurred in the Andaman Sea. Its epicenter was at 12.50 degrees North and 92.57 degrees East - about 9 degrees North of the epicenter of the 26 December 2004 earthquake, but within its tsunami generating area. This was the greatest earthquake in the Andaman and Nicobar Islands since the 31 December 1881 earthquake (M7.9) in the Nicobar Islands.

The 1941 earthquake was particularly destructive in the Middle and South Andaman Islands and caused considerable damage at Port Blair, Port Anson and surrounding areas. The earthquake ground motions were strong enough to be felt along the eastern coast of India, in Calcutta (now Kolkata), Chandernagar, Cuttack, Madras (now Chennai), in Colombo, Sri Lanka , and at Syhlet in Bangladesh. A series of strong aftershoks (two with magnitude 6.0 ) occurred within 24 hours of the main earthquake. Fourteen more earthquake aftershocks with magnitude 6.0 occurred until January 1942.

The earthquake generated a tsunami in the Bay of Bengal, but no estimates of wave heights are available According to reports, more than 5,000 people were killed on the east coast of India. The media incorrectly attributed the deaths and damage to storm surges rather than to a tsunami generated by an earthquake. Many more deaths must have occurred elsewhere but were not reported. World War II was in progress and communications were poor. Because of the war, losses of lives in remote areas from disasters did not get as much attention or media coverage. It is suspected that this tsunami caused many more deaths than what was reported. This event remains to be further investigated.

The Earthquake and Tsunami of 28 November 1945 in the Northern Arabian Sea

A great earthquake with moment magnitude Mw 8.0 (Richter Ms 7.8), occurred on 28 November 1945 (21:56 UTC) off the Makran coast of Pakistan. Its epicenter was at 24.5 N 63.0 E in the northern Arabian Sea, about 100 km south of Karachi. The earthquake generated a very destructive tsunami which affected Pakistan, the western coast of India, Iran and Oman, killing thousands of people and causing a great deal of destruction.

The tsunami was genetated along an active subduction zone off the Makran coast of Pakistan. This zone marks the boundary between the Arabian plate sliding beneath the Iranian micro-plate. A major fault which runs along the Makran coast is believed to be of the same character as the West Coast fault along the coast of Maharashtra, India.

The region of subduction along the Makran coast of Pakistan and the Gujarat Region of India where major earthquakes have occurred - one as recently as 2001.

PAKISTAN - The tsunami waves reached a maximum height of 40 feet along the Makran coast destroying fishing villages and causing great damage to port facilities. More than 4,000 people died from the combined earthquake and tsunami along the Makran coast, but most of the deaths were caused by the tsunami.

Tsunami waves of about 6.5 feet in height struck Karachi. There was no damage to the port and boats in Karachi Harbour. According to reports, the waves completely destroyed and killed all the people of the fishing village of Khudi, some 30 miles west of Karachi. There was considerable destruction and loss of life at the towns of Pasni and Ormara.

IRAN - There was considerable loss of life and destruction but no details are available.

INDIA - There was extensive destruction and loss of life along the west coast of India <(Salsette Island , Versova (Andheri), Haji Ali (Mahalaxmi), Juhu (Ville Parle) and Danda (Khar)>. The tsunami waves reached a height of 11.0 - 11.5 meters in Kutch, Gujarat. In Mumbai the height of the tsunami was 2 meters. The waves were recorded in Bombay Harbor but did not cause damage.

OMAN - There was considerable loss of life and destruction but no details are available. The tsunami was recorded at Muscat and Gwadar.

Future destructive tsunamis in the region could be generated from earthquakes along the subduction zone off the Makran coast or from a a major thrust fault along parts of deltaic Indus river.

(Excerpts from unpublished report by G. Pararas-Carayannis, "Seismo-Dynamics of Compressional Tectonic Collision - Potential for Tsunamigenesis Along Boundaries of the Indian, Eurasian and Arabian Plates" (Abstract submitted to the International Conference HAZARDS 2004, Hyderabad, India, 2-4 Dec. 2004 )

The Earthquake and Tsunami of 19 August 1977 in Indonesia - (Source: George Pararas-Carayannis 1977 survey in ITIC and ISU reports and Newsletters)

On August 19, 1977 (06:08:52.2 UTC) a major earthquake occurred in the Java Trench, westward of Sumba Island in Indonesia. This was the strongest earthquake in the Indian Ocean in several decades.The epicenter was 170 kilometers SSW of Pradapare (Sumba Island), at 11.09 S, 118.46 W. The quake was very widely felt and caused people in Perth, Australia, more than 2000 Km southward, to flee from office buildings. A major tsunami was generated which struck the coast of Sumba, Sumbawa, Lombok and Bali. In Kuta - Bali, one person was killed and 5 houses collapsed, 26 boats were broken or missing. On Lombok, 20 persons were killed, 115 houses damaged, 132 boats missing or broken. On Sumbawa, 81 people were killed, 53 people missing, more than 1000 people lost their properties, 63 houses, one school building, one mosque collapsed and the other was cracked. The quake also caused damage to some office buildings, school buildings, a mosque and a market in Sumbawa and Bima. In the entire Nusa Tenggara Islands region, the quake caused 107 deaths, with 54 people missing, 440 houses damaged/collapsed, 467 boats missing or broken, 5 school buildings collapsed and 3 teachers houses damaged.

The Lesser Sunda Islands where the 19 August 1977 Earthquake and Tsunami Occurred

Coastal roads did not exist in 1977 along the shores of the Lesser Sumba Islands fronting the Java Trench, but with the exception of Sumbawa some communities could be reached by road from the interior. Thus, no major ports were in the seriously struck areas, and casualties were relatively low. Incomplete reports indicated that more than 180 people died or presumed to be dead and that 3900 were left homeless. Property losses included homes, fishing boats, and gear. No tide records were available for most areas in Indonesia. However, on an inaccessible section of Sumbawa Island, a preliminary study indicated that the waves reached at least 15 meters above high tide, and penetrated about 500 meters inland in some valleys. Accounts given of the tsunami by observers at several locations have reasonable consistency.

The tsunami arrived on the Indonesian coast about an hour or two after high water, and begun with a recession that exposed the beach for 100-200 meters. Three large waves followed at intervals of perhaps 5 minutes or less, the first being the highest and most destructive. Residents in Sumbawa and Lombok communities reported that that before the quake and the tsunami arrival up to 3 unusual explosive sounds were heard over a period estimated from a few seconds to a minute or more. The sounds were described as those of bombs, of aircraft breaking the sound barrier, or thunder. The sound in each case came more or less from the direction of the earthquake's epicenter at sea. Almost every community reported the water turning black, and some claimed also that it increased in temperature and bad a bad odor.

Three major waves reportedly struck along the Australian coast ,the first being the largest, as in Indonesia. The sea level disturbances continued for several hours. The wave height was 2 meters at Dampier, 2 to 4 meters at Port Sampson, and 6 meters at Cape Leveque. The tsunami arrived as the tide was falling and, at most places, it was near low - which fortunately reduced the tsunami impact. There was apparently no loss of life in Australia, though it was reported that at least one person was swept into the sea by the waves.

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The Indian Ocean Tsunami of 2004: A Wake-Up Call

For many around the world, the day after Christmas is celebrated as another holiday, especially in Great Britain and nations where “Boxing Day” is a long-standing tradition. On that day in 2004, however, the world was shattered by one of the most devastating natural disasters in recorded history, forever changing humankind’s perception of tsunamis.

The Indian Ocean Earthquake and Tsunami killed approximately 228,000 people (the actual number is not known). Brought about by a massive and sudden uplifting of the subduction zone where the Burma and Indian Plates meet along the Sunda Trench, tsunami waves were generated that spread around the world, bringing wave heights of up to 100 feet to part of Indonesia. Property damage values amounted to more than $13 billion. The devastating tsunami was a grim reminder that existing forecasting abilities still needed to be improved, and served as a catalyst for that improvement, much of which would fall on NOAA and the National Weather Service.

The History of Tsunami Forecasting

In 1946, an 8.6 magnitude earthquake in Alaska caused a tsunami that killed more than 150 people in Hawaii--over 2,000 miles away from the epicenter. Two years later, in 1948, the Tsunami Warning System was born, with the intention of providing advance warnings and forecasts for impending tsunamis. Similarly, the Great Alaska Earthquake of 1964 served as a stark reminder that the tsunami threat was not just a distant concern, but could occur close to home. The U.S. West Coast and Alaska -- now National -- Tsunami Warning Center was established in 1967 specifically to provide warnings for these short-fused events.

Since then, NOAA (and its predecessor organizations) has been the federal agency responsible for tsunami warnings in the U.S. and its surrounding territories. From the late 1940s until very recently, scientists based tsunami warnings on the location and magnitude of earthquakes, combined with database information on past earthquakes and tsunamis. The warnings themselves consisted of the forecast arrival time of the first tsunami wave, and were directed at select locations around the Pacific Ocean basin likely to be affected. It was up to each nation to decide what actions to take along their coastlines, and the tsunami warning focal point would make that choice based on the size, location, and depth of an earthquake, taking into account the effects of past tsunamis on their coasts.

The Pacific Tsunami Warning Center (PTWC), the organization responsible for issuing tsunami watches and warnings, operated on the basis of extreme caution as a result, sometimes warnings or watches were issued that proved to be unnecessary, as a tsunami wasn’t generated. However, it was the position of the Center that it was far better to “overwarn” than “underwarn”, and that unnecessary, frequent warnings were preferable to not having warnings at all.

Beginning in the mid-1990s, NOAA began the process of modernizing and developing inundation forecast models for tsunamis with the goal of improving forecast and warning capabilities. In 1995, Congress directed NOAA to establish the National Tsunami Hazard Mitigation Program that sought to improve tsunami preparedness in U.S. coastal communities via improved warning guidance and hazard assessment. In addition, NOAA’s Pacific Marine Environmental Laboratory (PMEL) used a quarter century of tsunami research to develop and deploy real-time, deep-ocean tsunami measuring technology known as DART® (Deep-Ocean Assessment and Reporting of Tsunamis) buoys in the Pacific Ocean. The DART is a two-part device, consisting of a pressure sensor on the ocean floor that senses the presence of a tsunami wave and a surface buoy that receives information from the sensor. After receiving the data, the buoy then transmits this information via satellite to the National Data Buoy Center (NDBC), where it is relayed to the NWS Telecommunications Gateway. Once there, the data is placed on the Global Telecommunications System (GTS) and is then forwarded to the NOAA Tsunami Warning Centers in Hawaii and Alaska. With this technology, scientists are better able to determine whether or not the tsunami poses a threat to distant coastlines as it propagates across the ocean basin. The development of the DART, in addition to tsunami forecast models created by PMEL, enabled scientists to better predict time of arrival, height, and duration of tsunamis.

However, these advances did little to prepare those in the path of the Indian Ocean tsunami. Only a few DART buoys had been deployed then, and all in the Northern Hemisphere. Communications of tsunami warnings -- well established in the U.S., Japan, and other Northern Hemisphere nations -- were sorely lacking in the Southern Hemisphere. There was no advanced tsunami warning system in the Indian Ocean. Nevertheless, PTWC staff did what they could to warn nations of the danger, including working with the U.S. State Department to alert nations in East Africa well in advance of the tsunami's arrival, possible saving thousands of lives.

The Indian Ocean tragedy was a wake-up call to the world about the dangers of tsunami. In its aftermath, NOAA initiated a six-fold increase in the number of DART buoys in several oceans worldwide, and continued efforts to improve forecasting. Since their deployment, DART buoys around the world have detected 47 significant events.

In addition, NOAA scientists worked tirelessly to develop the modern system of tsunami forecasting. Today, using information about the shape and depth of the ocean bottom, as well as information about the topography of the shorelines, current forecasting models can now predict the arrival time, duration, height, and extent of flooding in specific locations for a tsunami. Additionally, today’s technology allows for increased knowledge of the fault geometry of the earthquake.

Preparing for a Tsunami Today and Tomorrow

Although tsunamis are among the rarest of natural disasters, their potential impacts are great. Fifteen years after that fateful morning, the United States and the world are much better prepared for, and ready to respond to, tsunami warnings when they occur.

In the wake of the Indian Ocean tsunami, the responsibilities of the National Weather Service’s Tsunami Warning Centers were expanded. Today, the National Tsunami Warning Center in Palmer, Alaska serves the continental United States, Alaska, and Canada. The PTWC in Honolulu, Hawaii directly serves the State of Hawaii, American Samoa, Guam and the Commonwealth of the Northern Marianas Islands, Puerto Rico, and the U.S. Virgin Islands. It is the primary Tsunami Service Provider for the Pacific and Caribbean ocean basins. The Intergovernmental Oceanographic Commission of UNESCO’s warning systems for the Pacific and Caribbean has two tsunami collaborative programs in which the U.S. participates: the Pacific Tsunami Warning System (PTWS), and the CARIBE-EWS for the Atlantic/Caribbean.

Educating and preparing communities vulnerable to tsunamis has also been a priority. The National Tsunami Hazard Mitigation Program -- a federal/state partnership that includes NOAA, the Federal Emergency Management Agency, the U.S. Geological Survey, and 28 U.S. states and territories -- works to reduce the impact of tsunamis through collaboration, coordination, and funding and technical support to partner states and territories. The NWS’ TsunamiReady® Program helps communities prepare for tsunamis through better planning, education, and awareness. Local NWS Weather Forecast Offices (WFOs) are responsible for implementing the TsunamiReady program in conjunction with state and local partners and working with communities to support their tsunami preparedness efforts. The WFOs also support the NOAA Tsunami Program by educating the public, local officials, and the media about tsunamis and tsunami safety, as well as disseminating tsunami messages. The Caribbean Tsunami Warning Program supports improved tsunami observations, provides training, outreach, and education assistance, and facilitates data exchange for domestic and international partners in the Caribbean and adjacent regions.

Despite the tragedy of the 2004 tsunami, the changes in technology and methods that came to be as a result have saved countless lives. Moving forward, scientists are hopeful that forecasting capabilities and the public’s greater understanding of tsunami dangers, preparedness, and response efforts will prevent a similar occurrence from ever happening again.


Tsunami devastates Indian Ocean coast - HISTORY

Tsunamis Through History

The world have been gripped by the devastation and tragedy after tsunamis decimated coastal areas of Southern Asia and East Africa on December 26th, 2004. Although it has been two weeks since, the tragedy is seemingly never ending, as the destruction caused by the ferocious waves have led to the deaths of over 150,000 people in 12 countries, as well as displacing millions more people who left to rely on international relief efforts.

As we have watched the unfolding of the tragic aftermath - the rising death toll rises, the images of whole villages wiped out, the wondering displaced in refugee-like camps, the immense aid and relief efforts &ndash many citizens of the world are only beginning to learn about the powerful force of a tsunami for the very first time.

The recent tsunami is the most devastating tsunami, in terms of claiming human lives, recorded in history. Although tsunamis are rare, there have been other significant tsunami that have occurred in all major oceans &ndash Indian, Pacific, and Atlantic &ndash since the dawn of civilization. References to these natural disastrous phenomena have been made backs as far as to the Ancient Greek and Roman civilizations. The United States National Oceanic and Atmospheric Administration estimates that on the average, there are two tsunamis per year somewhere in the world which cause damage near the source. Approximately every 15 years a tsunami causing wide spread destruction will usually occur.

The following is a historical overview of some of the most destructive tsunamis that have transpired since the dawn of civilization:

2004 Indian Ocean Tsunamis Affecting Southern Asia and Eastern Africa

A massive earthquake measuring over 9.0 on the Richter scale occurred under the Indian ocean floor just of the coast of the Indonesian island of Sumatra. Violent movement of the Earth's tectonic plates in this area displaced an enormous amount of water, sending powerful tsunami waves in every direction. Within hours killer tsunami waves radiating from the earthquake&rsquos epicenter slammed into the coastline of 12 Indian Ocean countries. The tsunami waves had heights reaching up to 15 meters (50 feet) which snatched people out to sea, drowning others in their homes or on beaches, and demolishing an immense amount of property in many areas.

The tsunamis generated by the earthquake have killed over the 150,000 people in twelve countries (Indonesia, India, Sri Lanka, Thailand, Malaysia, Maldives, Myanmar, Bangladesh, the Andaman and Nicobar Islands, the Maldives, Seychelles, Somalia, Tanzania, and Kenya). The hardest hit country was Indonesia, which was the closest to the earthquake&rsquos epicenter. The country have reported death tolls exceeding over 105,000 people with almost all mortalities from the Aceh Province at the northern end of the island of Sumatra.

1998 Tsunami Affecting Papua New Guinea

On July 17th, 1998, an earthquake measuring 7.1 on the Richter scale occurred about 15 miles just of the coast of northern Papua New Guinea, an island nation located in the southwestern Pacific Ocean just south of Indonesia and north of Australia. While the magnitude of the quake was not large enough to create the tsunami directly, it is believed the earthquake generated an undersea landslide, which in turn caused the tsunami. Following the earthquake, a tsunami with waves reaching 12 meters (40 feet) hit the Papua New Guinea coast within 10 minutes, destroying the villages of Arop and Warapu. An estimated 2,200 people were killed.

1976 Tsunami Affecting the Philippines

Around midnight on August 16th 1976, an earthquake measuring approximately 7.6 on the Richter scale occurred in the Moro Gulf a few miles away from the coast of the Philippine island of Mindanao. The earthquake itself was responsible for causing widespread damage, but its effect paled in comparison to the tsunami it helped created. The massive tsunami that devastated 700 kilometers of coastline bordering Moro Gulf in the North Celebes Sea, resulting in destruction and death in the coastal communities of the Sulu Archipelago and southern Mindanoa, including Zamboanga City and Pagadian City. Over 5,000 people were killed as they were swept out to sea, with thousands more remaining &ldquomissing&rdquo.

1964 Tsunami Affecting the West Coast of North America

Now known as the Good Friday Tsunami, the west coast, especially in the state of Alaska, was affected by a tsunami that was the most devastating ever in the continent of North America. On March 28th 1964, the United States experienced its biggest earthquake in history near College Fjord in Prince William Sound of the coast of Alaska that measured 9.2 on the Richter scale. The earthquake lasted for three to five minutes in most areas with jolting of the ocean floor creating large tsunamis. Although the earthquake did cause some destruction, the majority of death and property damage was caused by the resulting tsunami. The small Alaskan coastal communities of Girdwood, Portage, Vladez, and some native villages were absolutely decimated. There were a total of 106 people killed in Alaska due to the tsunami waves which reached heights of 11.5 meters (38 feet).

The tsunami traveled south along the west coast to impact the Canadian province of British Columbia. The mainland coast and Vancouver Island were affected where houses were seen being washed away to sea. Considerable damage was also felt in Crescent City, California where eleven people lost their lives. Even Hawaii, thousands of kilometers away felt the impact of the tsunami.

1960 Tsunami Affecting Chile and Pacific Nations

On May 22 1960, the biggest earthquake ever recorded at the time occurred just of the coast of South central Chile, a nation of South America. The earthquake measured 9.5 on the Richter scale with swarms of aftershock earthquakes that measured as large 8.0 that followed. The earthquakes triggered the creation of tsunami, which was responsible for most of the ensuing devastation and death.

The tsunami, together with the coastal subsidence and flooding, caused tremendous damage along the Chile coast, where about 2,000 people died. The waves spread outwards across the Pacific. Fifteen hours after the earthquake, tsunami waves flooded Hilo, on the island of Hawaii, where they built up to thirty feet and caused 61 deaths along the waterfront. Seven hours after that the waves flooded the coastline of Japan where ten-foot waves caused 200 deaths. Tsunami waves also caused damage in the Marquesas, in Samoa, and in New Zealand.

1896 Tsunami Affecting Japan

On June 15 1896, an earthquake occurred of the coast near the Japanese port city of Sanriku. The earthquake, which measured 7.2 on the Richter scale, triggered the formation a massive tsunami that devastated the city killing over 26,000 people. The tsunami waves reached an intimidating height of 25 meters (80 feet) as it crashed upon a crowd that had gathered in a city to celebrate a religious festival. The tsunami was also observed across the Pacific: In Hawaii, wharves were demolished and several houses were swept away. In California, a 9.5 feet wave was observed, according to the San Francisco Chronicle of June 16, 1896. This Sanriku tsunami served as an impetus for tsunami research in Japan.

What is unusual about this disaster is that the size of the tsunami was much larger than would be expected from the size of the earthquake, 7.2 on the Richter scale. At the time of the Sanriku tsunami earthquake, a weak shock was felt, followed by an extremely slow shaking that lasted about 5 minutes. Approximately 35 minutes after the earthquake, the large tsunami arrived at the Sanriku coast.

1883 Tsunami Affecting Indonesia

The volcanic explosion of Krakatoa is one of the most impressive natural disasters ever recorded in history. On August 26th 1883, the island volcano of Krakatoa exploded with devastating fury, blowing its underground magma chamber partly empty so that much overlying land and seabed collapsed into it. The great majority of the island simply was destroyed as it sank to the ocean floor. The volcanic disturbance triggered a series of large tsunami waves, some reaching a height of over 40 meters above sea level. Although no one is known to have been killed as a result of the initial explosion, the tsunamis it generated had disastrous results, killing over 36,000 people, and wiping out a number of settlements, including Telok Batong in Sumatra, and Sirik and Semarang in Java.

Tsunami waves were observed throughout the Indian Ocean, the Pacific Ocean, the American West Coast, South America, and even as far away as the English Channel. On the facing coasts of Java and Sumatra the sea flood went many miles inland and caused such vast loss of life that one area was never resettled but went back to the jungle and is now the Ujung Kulon nature reserve. Ships as far away as South Africa rocked as tsunamis hit them, and the bodies of victims were found floating in the ocean for weeks after the event. There are even numerous documented reports of groups of human skeletons floating across the Indian Ocean on rafts of volcanic pumice and washing up on the east coast of Africa up to a year after the eruption.

1755 Tsunami Affecting Portugal and Much of Europe

On November 1st 1755, one of the biggest earthquakes in history occurred in the Atlantic Ocean just of the coast of the Portuguese capital city of Lisbon. The total duration of shaking lasted ten minutes and was comprised of three distinct jolts. Scientists estimate that the earthquake was in the range of 9.0 on the Richter scale, which caused extensive damage throughout Lisbon. Surprisingly, the events that unfolded from this disaster has been well-documented.

After the earthquake, survivors rushed to the open space of the docks for safety and watched as the water receded, revealing the sea floor, littered by lost cargo and old shipwrecks. About 35 minutes after the initial earthquake, an enormous tsunami engulfed the Portuguese harbor and the city&rsquos downtown. Two other tsunamis followed to add to more devastation to the already suffering area. Effects from the earthquake and tsunamis were far reaching. The worst damage occurred in the south-west of Portugal, which included Lisbon. The tsunami reached, with less intensity, the coast of Spain, France, Great Britain, Ireland, Belgium and Holland. In Madeira and in the Azores islands damage was extensive and many ships were in danger of being wrecked. In total, over 100,000 people were killed, with most fatalities incurred in Lisbon, where over a third of the population were instantaneously wiped out. This tragic disaster served as the impetus for earthquake research in the world.


Contents

The 2004 Indian Ocean earthquake was initially documented as having a moment magnitude of 8.9. In February 2005, scientists revised the estimate of the magnitude to 9.0. [17] Although the Pacific Tsunami Warning Center has accepted these new numbers, the United States Geological Survey has so far not changed its estimate of 9.1. A 2006 study estimated a magnitude of Mw 9.1–9.3 Hiroo Kanamori of the California Institute of Technology estimates that Mw 9.2 is representative of the earthquake's size. [18]

The hypocentre of the main earthquake was approximately 160 km (100 mi) off the western coast of northern Sumatra, in the Indian Ocean just north of Simeulue island at a depth of 30 km (19 mi) below mean sea level (initially reported as 10 km or 6.2 mi). The northern section of the Sunda megathrust ruptured over a length of 1,300 km (810 mi). [15] The earthquake (followed by the tsunami) was felt in Bangladesh, India, Malaysia, Myanmar, Thailand, Sri Lanka and the Maldives. [19] Splay faults, or secondary "pop up faults", caused long, narrow parts of the seafloor to pop up in seconds. This quickly elevated the height and increased the speed of waves, destroying the nearby Indonesian town of Lhoknga. [20]

Indonesia lies between the Pacific Ring of Fire along the north-eastern islands adjacent to New Guinea, and the Alpide belt that runs along the south and west from Sumatra, Java, Bali, Flores to Timor. The 2002 Sumatra earthquake is believed to have been a foreshock, preceding the main event by over two years. [21]

Great earthquakes, such as the 2004 Indian Ocean earthquake, are associated with megathrust events in subduction zones. Their seismic moments can account for a significant fraction of the global seismic moment across century-scale periods. Of all the moment released by earthquakes in the 100 years from 1906 through 2005, roughly one eighth was due to the 2004 Indian Ocean earthquake. This quake, together with the Good Friday earthquake (Alaska, 1964) and the Great Chilean earthquake (1960), account for almost half of the total moment. [ citation needed ]

Since 1900, the only earthquakes recorded with a greater magnitude were the 1960 Great Chilean earthquake (magnitude 9.5) and the 1964 Good Friday earthquake in Prince William Sound (magnitude 9.2). The only other recorded earthquakes of magnitude 9.0 or greater were off Kamchatka, Russia, on 4 November 1952 (magnitude 9.0) and Tōhoku, Japan (magnitude 9.1) in March 2011. Each of these megathrust earthquakes also spawned tsunamis in the Pacific Ocean. In comparison to the 2004 Indian Ocean earthquake, the death toll from these earthquakes was significantly lower, primarily because of the lower population density along the coasts near affected areas, the much greater distances to more populated coasts, and the superior infrastructure and warning systems in MEDCs (More Economically Developed Countries) such as Japan. [ citation needed ]

Other huge megathrust earthquakes occurred in 1868 (Peru, Nazca Plate and South American Plate) 1827 (Colombia, Nazca Plate and South American Plate) 1812 (Venezuela, Caribbean Plate and South American Plate) and 1700 (western North America, Juan de Fuca Plate and North American Plate). All of them are believed to be greater than magnitude 9, but no accurate measurements were available at the time. [ citation needed ]

Tectonic plates

The 2004 Indian Ocean earthquake was unusually large in geographical and geological extent. An estimated 1,600 km (1,000 mi) of fault surface slipped (or ruptured) about 15 m (50 ft) along the subduction zone where the Indian Plate slides (or subducts) under the overriding Burma Plate. The slip did not happen instantaneously but took place in two phases over several minutes: Seismographic and acoustic data indicate that the first phase involved a rupture about 400 km (250 mi) long and 100 km (60 mi) wide, 30 km (19 mi) beneath the sea bed—the largest rupture ever known to have been caused by an earthquake. The rupture proceeded at about 2.8 km/s (1.7 mi/s 10,000 km/h 6,300 mph), beginning off the coast of Aceh and proceeding north-westerly over about 100 seconds. After a pause of about another 100 seconds, the rupture continued northwards towards the Andaman and Nicobar Islands. The northern rupture occurred more slowly than in the south, at about 2.1 km/s (1.3 mi/s 7,600 km/h 4,700 mph), continuing north for another five minutes to a plate boundary where the fault type changes from subduction to strike-slip (the two plates slide past one another in opposite directions).

The Indian Plate is part of the great Indo-Australian Plate, which underlies the Indian Ocean and Bay of Bengal, and is moving north-east at an average of 60 mm/a (0.075 in/Ms). The India Plate meets the Burma Plate (which is considered a portion of the great Eurasian Plate) at the Sunda Trench. At this point, the India Plate subducts beneath the Burma Plate, which carries the Nicobar Islands, the Andaman Islands, and northern Sumatra. The India Plate sinks deeper and deeper beneath the Burma Plate until the increasing temperature and pressure drive volatiles out of the subducting plate. These volatiles rise into the overlying plate, causing partial melting and the formation of magma. The rising magma intrudes into the crust above and exits the Earth's crust through volcanoes in the form of a volcanic arc. The volcanic activity that results as the Indo-Australian Plate subducts the Eurasian Plate has created the Sunda Arc.

As well as the sideways movement between the plates, the 2004 Indian Ocean earthquake resulted in a rise of the seafloor by several metres, displacing an estimated 30 km 3 (7.2 cu mi) of water and triggering devastating tsunami waves. The waves radiated outwards along the entire 1,600 km (1,000 mi) length of the rupture (acting as a line source). This greatly increased the geographical area over which the waves were observed, reaching as far as Mexico, Chile, and the Arctic. The raising of the seafloor significantly reduced the capacity of the Indian Ocean, producing a permanent rise in the global sea level by an estimated 0.1 mm (0.004 in). [22]

Aftershocks and other earthquakes

Numerous aftershocks were reported off the Andaman Islands, the Nicobar Islands and the region of the original epicentre in the hours and days that followed. The magnitude 8.7 2005 Nias–Simeulue earthquake, which originated off the coast of the Sumatran island of Nias, is not considered an aftershock, despite its proximity to the epicentre, and was most likely triggered by stress changes associated with the 2004 event. [23] The earthquake produced its own aftershocks (some registering a magnitude of as high as 6.1) and presently ranks as the third-largest earthquake ever recorded on the moment magnitude or Richter magnitude scale.

Other aftershocks of up to magnitude 6.6 continued to shake the region daily for three or four months. [24] As well as continuing aftershocks, the energy released by the original earthquake continued to make its presence felt well after the event. A week after the earthquake, its reverberations could still be measured, providing valuable scientific data about the Earth's interior.

The 2004 Indian Ocean earthquake came just three days after a magnitude 8.1 earthquake in the sub-antarctic Auckland Islands, an uninhabited region west of New Zealand, and Macquarie Island to Australia's north. This is unusual since earthquakes of magnitude eight or more occur only about once per year on average. [25] The U.S. Geological Survey sees no evidence of a causal relationship between these events. [26]

The 2004 Indian Ocean earthquake is thought to have triggered activity in both Leuser Mountain [27] and Mount Talang, [28] volcanoes in Aceh along the same range of peaks, while the 2005 Nias–Simeulue earthquake had sparked activity in Lake Toba, an ancient crater in Sumatra. [29]

Energy released

The energy released on the Earth's surface (ME, which is the seismic potential for damage) by the 2004 Indian Ocean earthquake was estimated at 1.1 × 10 17 joules (110 PJ 26 Mt). [30] This energy is equivalent to over 1,500 times that of the Hiroshima atomic bomb, but less than that of Tsar Bomba, the largest nuclear weapon ever detonated. The total physical work done MW (and thus energy) by the quake was 4.0 × 10 22 joules (40 ZJ), [31] the vast majority underground, which is over 360,000 times more than its ME, equivalent to 9,600 gigatons of TNT equivalent (550 million times that of Hiroshima) or about 370 years of energy use in the United States at 2005 levels of 1.08 × 10 20 joules (108 EJ). The only recorded earthquakes with a larger MW were the 1960 Chilean and 1964 Alaskan quakes, with 2.5 × 10 23 joules (250 ZJ) and 7.5 × 10 22 joules (75 ZJ), respectively. [32]

The earthquake generated a seismic oscillation of the Earth's surface of up to 200–300 mm (8–12 in), equivalent to the effect of the tidal forces caused by the Sun and Moon. The seismic waves of the earthquake were felt across the planet as far away as the U.S. state of Oklahoma, where vertical movements of 3 mm (0.12 in) were recorded. By February 2005, the earthquake's effects were still detectable as a 20 μm (0.02 mm 0.0008 in) complex harmonic oscillation of the Earth's surface, which gradually diminished and merged with the incessant free oscillation of the Earth more than four months after the earthquake. [33]

Because of its enormous energy release and shallow rupture depth, the earthquake generated remarkable seismic ground motions around the globe, particularly due to huge Rayleigh (surface) elastic waves that exceeded 10 mm (0.4 in) in vertical amplitude everywhere on Earth. The record section plot displays vertical displacements of the Earth's surface recorded by seismometers from the IRIS/USGS Global Seismographic Network plotted with respect to time (since the earthquake initiation) on the horizontal axis, and vertical displacements of the Earth on the vertical axis (note the 1 cm scale bar at the bottom for scale). The seismograms are arranged vertically by distance from the epicentre in degrees. The earliest, lower amplitude signal is that of the compressional (P) wave, which takes about 22 minutes to reach the other side of the planet (the antipode in this case near Ecuador). The largest amplitude signals are seismic surface waves that reach the antipode after about 100 minutes. The surface waves can be clearly seen to reinforce near the antipode (with the closest seismic stations in Ecuador), and to subsequently encircle the planet to return to the epicentral region after about 200 minutes. A major aftershock (magnitude 7.1) can be seen at the closest stations starting just after the 200-minute mark. The aftershock would be considered a major earthquake under ordinary circumstances but is dwarfed by the mainshock.

The shift of mass and the massive release of energy slightly altered the Earth's rotation. The exact amount is not yet known, but theoretical models suggest the earthquake shortened the length of a day by 2.68 microseconds, due to a decrease in the oblateness of the Earth. [34] It also caused the Earth to minutely "wobble" on its axis by up to 25 mm (1 in) in the direction of 145° east longitude, [35] or perhaps by up to 50 or 60 mm (2.0 or 2.4 in). [36] Because of tidal effects of the Moon, the length of a day increases at an average of 15 microseconds per year, so any rotational change due to the earthquake will be lost quickly. Similarly, the natural Chandler wobble of the Earth, which in some cases can be up to 15 m (50 ft), will eventually offset the minor wobble produced by the earthquake.

There was 10 m (33 ft) movement laterally and 4–5 m (13–16 ft) vertically along the fault line. Early speculation was that some of the smaller islands south-west of Sumatra, which is on the Burma Plate (the southern regions are on the Sunda Plate), might have moved south-west by up to 36 m (120 ft), but more accurate data released more than a month after the earthquake found the movement to be about 0.2 m (8 in). [37] Since movement was vertical as well as lateral, some coastal areas may have been moved to below sea level. The Andaman and Nicobar Islands appear to have shifted south-west by around 1.25 m (4 ft 1 in) and to have sunk by 1 m (3 ft 3 in). [38]

In February 2005, the Royal Navy vessel HMS Scott surveyed the seabed around the earthquake zone, which varies in depth between 1,000 and 5,000 m (550 and 2,730 fathoms 3,300 and 16,400 ft). The survey, conducted using a high-resolution, multi-beam sonar system, revealed that the earthquake had made a considerable impact on the topography of the seabed. 1,500-metre-high (5,000 ft) thrust ridges created by previous geologic activity along the fault had collapsed, generating landslides several kilometres wide. One such landslide consisted of a single block of rock some 100 m (330 ft) high and 2 km (1.2 mi) long. The momentum of the water displaced by tectonic uplift had also dragged massive slabs of rock, each weighing millions of tonnes, as far as 10 km (6 mi) across the seabed. An oceanic trench several kilometres wide was exposed in the earthquake zone. [39]

The TOPEX/Poseidon and Jason-1 satellites happened to pass over the tsunami as it was crossing the ocean. [40] These satellites carry radars that measure precisely the height of the water surface anomalies in the order of 500 mm (20 in) were measured. Measurements from these satellites may prove invaluable for the understanding of the earthquake and tsunami. [41] Unlike data from tide gauges installed on shores, measurements obtained in the middle of the ocean can be used for computing the parameters of the source earthquake without having to compensate for the complex ways in which proximity to the coast changes the size and shape of a wave.

The sudden vertical rise of the seabed by several metres during the earthquake displaced massive volumes of water, resulting in a tsunami that struck the coasts of the Indian Ocean. A tsunami that causes damage far away from its source is sometimes called a teletsunami and is much more likely to be produced by the vertical motion of the seabed than by horizontal motion. [42]

The tsunami, like all others, behaved differently in deep water than in shallow water. In deep ocean water, tsunami waves form only a low, broad hump, barely noticeable and harmless, which generally travels at high speed of 500 to 1,000 km/h (310 to 620 mph) in shallow water near coastlines, a tsunami slows down to only tens of kilometres per hour but, in doing so, forms large destructive waves. Scientists investigating the damage in Aceh found evidence that the wave reached a height of 24 m (80 ft) when coming ashore along large stretches of the coastline, rising to 30 m (100 ft) in some areas when travelling inland. [4] Radar satellites recorded the heights of tsunami waves in deep water: maximum height was at 600 mm (2 ft) two hours after the earthquake, the first such observations ever made. [43] [44]

According to Tad Murty, vice-president of the Tsunami Society, the total energy of the tsunami waves was equivalent to about 5 megatons of TNT (21 PJ), which is more than twice the total explosive energy used during all of World War II (including the two atomic bombs) but still a couple of orders of magnitude less than the energy released in the earthquake itself. In many places, the waves reached as far as 2 km (1.2 mi) inland. [45]

Because the 1,600 km (1,000 mi) fault affected by the earthquake was in a nearly north–south orientation, the greatest strength of the tsunami waves was in an east–west direction. Bangladesh, which lies at the northern end of the Bay of Bengal, had few casualties despite being a low-lying country relatively near the epicentre. It also benefited from the fact that the earthquake proceeded more slowly in the northern rupture zone, greatly reducing the energy of the water displacements in that region.

Coasts that have a landmass between them and the tsunami's location of origin are usually safe however, tsunami waves can sometimes diffract around such landmasses. Thus, the state of Kerala was hit by the tsunami despite being on the western coast of India, and the western coast of Sri Lanka suffered substantial impacts. Distance alone was no guarantee of safety, as Somalia was hit harder than Bangladesh despite being much farther away.

Because of the distances involved, the tsunami took anywhere from fifteen minutes to seven hours to reach the coastlines. [46] [47] The northern regions of the Indonesian island of Sumatra were hit quickly, while Sri Lanka and the east coast of India were hit roughly 90 minutes to two hours later. Thailand was struck about two hours later despite being closer to the epicentre because the tsunami travelled more slowly in the shallow Andaman Sea off its western coast.

The tsunami was noticed as far as Struisbaai in South Africa, about 8,500 km (5,300 mi) away, where a 1.5-metre-high (5 ft) tide surged on shore about 16 hours after the earthquake. It took a relatively long time to reach Struisbaai at the southernmost point of Africa, probably because of the broad continental shelf off South Africa and because the tsunami would have followed the South African coast from east to west. The tsunami also reached Antarctica, where tidal gauges at Japan's Showa Base recorded oscillations of up to a metre (3 ft 3 in), with disturbances lasting a couple of days. [48]

Some of the tsunami's energy escaped into the Pacific Ocean, where it produced small but measurable tsunamis along the western coasts of North and South America, typically around 200 to 400 mm (7.9 to 15.7 in). [49] At Manzanillo, Mexico, a 2.6 m (8.5 ft) crest-to-trough tsunami was measured. As well, the tsunami was large enough to be detected in Vancouver, which puzzled many scientists, as the tsunamis measured in some parts of South America were larger than those measured in some parts of the Indian Ocean. It has been theorized that the tsunamis were focused and directed at long ranges by the mid-ocean ridges which run along the margins of the continental plates. [50]

Early signs and warnings

Despite a delay of up to several hours between the earthquake and the impact of the tsunami, nearly all of the victims were taken by surprise. There were no tsunami warning systems in the Indian Ocean to detect tsunamis or to warn the general population living around the ocean. [51] Tsunami detection is not easy because while a tsunami is in deep water, it has little height and a network of sensors is needed to detect it.

Tsunamis are more frequent in the Pacific Ocean than in other oceans because of earthquakes in the "Ring of Fire". Although the extreme western edge of the Ring of Fire extends into the Indian Ocean (the point where the earthquake struck), no warning system exists in that ocean. Tsunamis there are relatively rare despite earthquakes being relatively frequent in Indonesia. The last major tsunami was caused by the 1883 eruption of Krakatoa. Not every earthquake produces large tsunamis: on 28 March 2005, a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean but did not result in a major tsunami.

The first warning sign of a possible tsunami is the earthquake itself. However, tsunamis can strike thousands of kilometres away where the earthquake is felt only weakly or not at all. Also, in the minutes preceding a tsunami strike, the sea sometimes recedes temporarily from the coast, which was observed on the eastern earthquake rupture zone such as the coastlines of Aceh, Phuket island, and Khao Lak area in Thailand, Penang island of Malaysia, and the Andaman and Nicobar islands. This rare sight reportedly induced people, especially children, to visit the coast to investigate and collect stranded fish on as much as 2.5 km (1.6 mi) of exposed beach, with fatal results. [52] However, not all tsunamis cause this "disappearing sea" effect. In some cases, there are no warning signs at all: the sea will suddenly swell without retreating, surprising many people and giving them little time to flee.

One of the few coastal areas to evacuate ahead of the tsunami was on the Indonesian island of Simeulue, close to the epicentre. Island folklore recounted an earthquake and tsunami in 1907, and the islanders fled to inland hills after the initial shaking and before the tsunami struck. These tales and oral folklore from previous generations may have helped the survival of the inhabitants. [53] On Maikhao Beach in north Phuket City, Thailand, a 10-year-old British tourist named Tilly Smith had studied tsunamis in geography at school and recognised the warning signs of the receding ocean and frothing bubbles. She and her parents warned others on the beach, which was evacuated safely. [54] John Chroston, a biology teacher from Scotland, also recognised the signs at Kamala Bay north of Phuket, taking a busload of vacationers and locals to safety on higher ground.

Anthropologists had initially expected the aboriginal population of the Andaman Islands to be badly affected by the tsunami and even feared the already depopulated Onge tribe could have been wiped out. [55] Many of the aboriginal tribes evacuated and suffered fewer casualties, however. [56] [57] Oral traditions developed from previous earthquakes helped the aboriginal tribes escape the tsunami. For example, the folklore of the Onges talks of "huge shaking of ground followed by high wall of water". Almost all of the Onge people seemed to have survived the tsunami. [58]

Indonesia

The tsunami devastated the coastline of Aceh province, about 20 minutes after the earthquake. Banda Aceh, the closest major city suffered severe casualties, with about 167,000 people perishing. The sea receded and exposed the seabed, prompting locals to collect stranded fish and explore the area. Local eyewitnesses described three large waves, with the first wave rising gently to the foundation of the buildings, followed minutes later by a sudden withdrawal of the sea near the port of Ulee Lheue. This was succeeded by the appearance of two large black-coloured steep waves which then travelled inland into the capital city as a large turbulent bore. Eyewitnesses described the tsunami as a "black giant", "mountain" and a "wall of water". Video footage revealed torrents of black water, surging by windows of a two-story residential area situated about 3.2 km (2.0 mi) inland. Additionally, amateur footage recorded in the middle of the city captured an approaching black surge flowing down the city streets, full of debris, inundating them. [59]

The level of destruction was extreme on the northwestern areas of the city, immediately inland of the aquaculture ponds, and directly facing the Indian Ocean. The tsunami height was reduced from 12 m (39 ft) at Ulee Lheue to 6 m (20 ft) a further 8 km (5.0 mi) to the north-east. The inundation was observed to extend 3–4 km (1.9–2.5 mi) inland throughout the city. Within 2–3 km (1.2–1.9 mi) of the shoreline, houses, except for strongly-built reinforced concrete ones with brick walls, which seemed to have been partially damaged by the earthquake before the tsunami attack, were swept away or destroyed by the tsunami. [60] [61] The area toward the sea was wiped clean of nearly every structure, while closer to the river, dense construction in a commercial district showed the effects of severe flooding. The flow depth at the city was just at the level of the second floor, and there were large amounts of debris piled along the streets and in the ground-floor storefronts. In the seaside section of Ulee Lheue, the flow depths were over 9 m (30 ft). Footage showed evidence of back-flowing of the Aceh River, carrying debris and people from destroyed villages at the coast and transporting them up to 40 km (25 mi) inland. [62]

A group of small islands: Weh, Breueh, Nasi, Teunom, Bunta, Lumpat and Batee island lie just north of the capital city. The tsunami reached a run-up of 10–20 m (33–66 ft) on the western shoreline of Breueh Island and Nasi Island. Coastal villages were destroyed by the tsunami waves. On Pulau Weh, the island experienced strong surges in the port of Sabang, yet there was little damage with a reported runup values of 3–5 m (9.8–16.4 ft), most likely due to the island being sheltered from the direct tsunami attack by the islands to the south-west. [61]

Lhoknga is a small coastal community about 13 km (8.1 mi) south-west of Banda Aceh, located on a flat coastal plain in between two rainforest-covered hills, overlooking a large bay and famous for its large swathe of white sandy beach and surfing activities. The locals reported 10 to 12 tsunamis, with the second and third waves being the highest and most destructive. Interview with the locals revealed that the sea temporarily receded and exposed coral reefs. In the distant horizon, gigantic black waves about 30 m (98 ft) high made explosion-like sounds as it broke and approached the shore. The first wave came rapidly landward from the south-west as a turbulent bore about 0.5–2.5 m (1.6–8.2 ft) high. The second and third waves were 15–30 m (49–98 ft) high at the coast and appeared like gigantic surfing waves but "taller than the coconut trees and was like a mountain". [63] The second wave was the largest it came from the west-southwest within five minutes of the first wave. The tsunami stranded cargo ships, barges and destroyed a cement mining facility near the Lampuuk coast, where the tsunami reached the fourth level of the building. [5] [64] [65]

Meulaboh, a remote coastal city, was among the hardest hit by the tsunami. The waves arrived after the sea receded about 500 m (1,600 ft), followed by an advancing small tsunami. The second and third destructive waves arrived later, which exceeded the height of the coconut trees. The inundation distance is about 5 km (3.1 mi). Other towns on Aceh's west coast hit by the disaster included Leupung, Lhokruet, Lamno, Patek, Calang, and Teunom. Affected or destroyed towns on the region's north and east coast were Pidie Regency, Samalanga, Panteraja, and Lhokseumawe. The high fatality rate in the area was mainly due to lack of preparation of the community towards a tsunami and limited knowledge and education among the population regarding the natural phenomenon. Helicopter surveys showed entire settlements virtually destroyed with destruction within miles inland, and only some mosques left standing. [66]

The greatest run-up height of the tsunami was measured at a hill between Lhoknga and Leupung, on the western coast of the northern tip of Sumatra, near Banda Aceh, and reached 51 m (167 ft). [5] [67]

The tsunami heights in Sumatra: [60]

  • 15–30 m (49–98 ft) on the west coast of Aceh
  • 6–12 m (20–39 ft) on the Banda Aceh coast
  • 6 m (20 ft) on the Krueng Raya coast
  • 5 m (16 ft) on the Sigli coast
  • 3–6 m (9.8–19.7 ft) on the north coast of Weh Island directly facing the tsunami source
  • 3 m (9.8 ft) on the opposite side of the coast of Weh Island facing the tsunami

Sri Lanka

The island country of Sri Lanka, located about 1,700 km (1,100 mi) from Sumatra, was ravaged by the tsunami around 2 hours after the earthquake. The tsunami first struck the eastern coastline and subsequently refracted around the southern point of Sri Lanka (Dondra Head). The refracted tsunami waves then inundated the southwestern part of Sri Lanka after some of its energy was reflected from impact with the Maldives. [68] In Sri Lanka, the civilian casualties were second only to those in Indonesia, with approximately 35,000 killed by the tsunami. The eastern shores of Sri Lanka were the hardest hit since it faced the epicentre of the earthquake, while the southwestern shores were hit later, but the death toll was just as severe. The southwestern shores are a hotspot for tourists and fishing. [69] The degradation of the natural environment in Sri Lanka contributed to the high death tolls. Approximately 90,000 buildings and many wooden houses were destroyed. [69]

The tsunami arrived on the island as a small brown-orange colored flood. Moments later, the ocean floor was exposed to as much as 1 km (0.62 mi) in places, which was followed by a massive second and third tsunami wave. Amateur video recorded at the city of Galle showed a large deluge flooding the city, carrying debris and sweeping away people while in the coastal resort town of Beruwala, the tsunami appeared as a huge brown-orange colored bore which reached the first level of a hotel, causing destruction and taking people unaware. Other videos recorded showed that the tsunami appeared like a flood raging inland. The construction of seawalls and breakwaters reduced the power of waves at some locations.

The largest run-up measured was at 12.5 m (41 ft) with inundation distance of 390–1,500 m (1,280–4,920 ft) in Yala. [70] In Hambantota, tsunami run-ups measured 11 m (36 ft) with the greatest inundation distance of 2 km (1.2 mi). Tsunami run-up measurements along the Sri Lankan coasts are at 2.4–4.11 m (7 ft 10 in–13 ft 6 in). [70] [68] Tsunami waves measured on the east coast ranged from 4.5–9 m (15–30 ft) at Pottuvill to Batticaloa at 2.6–5 m (8 ft 6 in–16 ft 5 in) in the north-east around Trincomalee and 4–5 m (13–16 ft) in the west coast from Moratuwa to Ambalangoda.

Sri Lanka tsunami height survey:

  • 9 m (30 ft) at Koggala
  • 6 m (20 ft) at Galle port
  • 4.8 m (16 ft) around the Galle coast
  • 8.7 m (29 ft) at Nonagama
  • 4.9 m (16 ft) at Weligama
  • 4 m (13 ft) at Dodundawa
  • 4.7 m (15 ft) at Ambalangoda
  • 4.7 m (15 ft) at Hikkaduwa Fishery Harbour
  • 10 m (33 ft) at Kahawa
  • 4.8 m (16 ft) at North Beach of Beruwala
  • 6 m (20 ft) at Paiyagala

A regular passenger train operating between Maradana and Matara was derailed and overturned by the tsunami and claimed at least 1,700 lives, the largest single rail disaster death toll in history. [71] Estimates based on the state of the shoreline and a high-water mark on a nearby building place the tsunami 7.5–9 m (25–30 ft) above sea level and 2–3 m (6 ft 7 in–9 ft 10 in) higher than the top of the train.

Thailand

The tsunami travelled eastward through the Andaman Sea and hit the south-western coasts of Thailand, about 2 hours after the earthquake. Located about 500 km (310 mi) from the epicentre, at the time, the region was popular with tourists because of Christmas. Many of these tourists were caught off-guard by the tsunami, as they had no prior warning. The tsunami hit during high tide. Major locations damaged included the western shores of Phuket island, the resort town of Khao Lak in Phang Nga Province, the coastal provinces of Krabi, Satun, Ranong and Trang and small offshore islands like Ko Racha Yai, the Phi Phi islands, the Surin Islands and the Similan archipelago. Approximately 8,000 people were killed.

Thailand experienced the second largest tsunami run-up. The tsunami heights recorded: [72] [73]

  • 6–10 m (20–33 ft) in Khao Lak
  • 3–6 m (9.8–19.7 ft) along the west coast of Phuket island
  • 3 m (9.8 ft) along the south coast of Phuket island
  • 2 m (6 ft 7 in) along the east coast of Phuket island
  • 4–6 m (13–20 ft) on the Phi Phi Islands
  • 19.6 m (64 ft) at Ban Thung Dap
  • 5 m (16 ft) at Ramson
  • 6.8 m (22 ft) at Ban Thale Nok
  • 5 m (16 ft) at Hat Praphat (Ranong Coastal Resources Research Station)
  • 6.3 m (21 ft) at Thai Mueang District
  • 6.8 m (22 ft) at Rai Dan

The province of Phang Nga was the most affected area in Thailand. The quiet resort town of Khao Lak is located on a stretch of golden sandy beach, famed for its hotels overlooking the Andaman Sea and hilly rainforests. A video, documented by a local restaurant manager from a hill adjacent to the beach, showed that the tsunami's arrival was preceded by a sudden retreat of the sea exposing the seafloor. Many tourists and locals can be seen trying to gather fish and moments later, the tsunami can be seen suddenly as a turbulent bore and inundating a person, several people and the hotels inland. Another amateur video, captured by a German family at beach level, showed the tsunami appearing as a white horizontal line in the distant horizon, gradually becoming bigger (bore-like), engulfing a jet skier and lifting two police boats. [74] A maximum inundation of approximately 2 km (1.2 mi) was measured, the inundated depths were 4–7 m (13–23 ft) and there was evidence that the tsunami reached the third floor of a resort hotel. The tsunami in Khao Lak was bigger due to offshore coral reefs and shallow seafloor which caused the tsunami to pile-up. This was similar to eyewitness accounts of the tsunami at Banda Aceh.

Khao Lak also experienced the largest tsunami run-up height outside of Sumatra. [72] [ page needed ] . The highest-recorded tsunami run-up was measured 19.6 m (64 ft) at Ban Thung Dap, on the south-west tip of Ko Phra Thong Island and the second-highest at 15.8 m (52 ft) at Ban Nam Kim. [73] Moreover, the largest death toll occurred at Khao Lak, with about 5,000 people killed.

In addition, the tsunami inflicted damage to the popular resort town of Ao Nang in Krabi Province. Video footage showed that the tsunami appeared as multiple white surfs violently lifting up yachts, boats and crashing onto beaches. Footage captured at Koh Lanta showed a wall of water swamping the beach, while another video taken at another location showed a large surfing wave like tsunami approaching the shore, lifting up a yacht and flooding the beach. At Koh Sriboya, the tsunami advanced inland as a turbulent medium bore, while at Koh Phayam, Ranong Province, the tsunami appeared as a wall of water.

At Phuket Province, the island province's western beaches were struck by the tsunami. At Patong Beach, a tourist mecca, the tsunami first arrived as a small flood, which swept away cars and unexpected people. About 10 minutes later, the sea receded for a while before the tsunami arrived again as a large wall of water looming over the skyline and flooding the coast. Another video from Kamala Beach showed the tsunami flooding the ground floor of a restaurant sweeping away an elderly couple. On Karon Beach, Kamala Beach and Kata Beach, the tsunami came in like a surging flood inland carrying people and cars. On some locations, a coastal road was built which was higher than the shore, protecting a hotel which was behind it. On the east coast of Phuket Island, the tsunami height was about 2 m. In one river mouth, many boats were damaged. The tsunami moved counter-clockwise around Phuket Island, as was the case at Okushiri Island in the 1993 Hokkaido earthquake. According to interviews, the second wave was the largest. [72] The tsunami heights were 5–6 m (16–20 ft) and the inundated depth was about 2 m (6.6 ft). The tsunami surprised many tourists at Koh Racha Yai, where it flooded the resorts. About 250 people perished directly in the tsunami.

The Phi Phi Islands are a group of small islands that were affected by the tsunami. The north bay of Phi Phi Don Island opens to the north-west in the direction of the tsunami. The measured tsunami height on this beach was 5.8 m (19 ft). According to eyewitness accounts, the tsunami came from the north and south. The ground level was about 2 m above sea level, and there were many cottages and hotels. The south bay opens to the south-east and faces in the opposite direction from the tsunami. Furthermore, Phi Phi Le Island shields the port of Phi Phi Don Island. The measured tsunami height was 4.6 m (15 ft) in the port. [72] Amateur camcorder footage taken by Israeli tourists showed the tsunami advancing inland suddenly as a small flood, gradually becoming more powerful and engulfed the whole beach and resort, with a yacht boat can be seen carried by the tsunami out to sea.

Moreover, the tsunami was detected by scuba divers around offshore islands like the Similan Islands and the Surin Islands. The divers reported being caught in a violent, swirling current suddenly while underwater. Local camcorder footage showed the tsunami surging inland and flooding camping equipment at the Similan Islands while the tsunami caught tourists unaware at the Surin Islands, and dragging them out towards the sea.

India

The tsunami reached the states of Andhra Pradesh and Tamil Nadu along the southeastern coastline of the Indian mainland about 2 hours after the earthquake. At the same time, it arrived in the state of Kerala, on the southwestern coast. There were two to five tsunamis that coincided with the local high tide in some areas. [75] [76] [77] [78]

The tsunami runup height measured in mainland India by Ministry of Home Affairs includes: [78]

  • 3.4 m (11 ft) at Kerala, inundation distance of 0.5–1.5 km (0.31–0.93 mi) with 250 km (160 mi) of coastline affected
  • 4.5 m (15 ft) at the southern coastline of Tamil Nadu, inundation distance of 0.2–2 km (0.12–1.24 mi) with 100 km (62 mi) of coastline affected
  • 5 m (16 ft) at the eastern coastline of Tamil Nadu facing tsunami source, inundation distance of 0.4–1.5 km (0.25–0.93 mi) with 800 km (500 mi) of coastline affected
  • 4 m (13 ft) at Pondicherry, inundation distance of 0.2–2 km (0.12–1.24 mi) with 25 km (16 mi) of coastline affected
  • 2.2 m (7.2 ft) at Andhra Pradesh, inundation distance of 0.2–1 km (0.12–0.62 mi) with 985 km (612 mi) of coastline affected

Along the coast of Tamil Nadu, the 13 km (8.1 mi) Marina Beach in Chennai was battered by the tsunami which swept across the beach taking morning walkers unaware. Amateur video recorded taken at a resort beach showed the tsunami arriving as a large wall of water as it approached the coast and flooding it as it advanced inland. Besides that, a 10 m (33 ft) black muddy tsunami ravaged the city of Karaikal, where 492 lives were lost. The city of Pondicherry, protected by seawalls was relatively unscathed. Local video recorded that before the arrival of the tsunami, people can be seen swarming the beach to check on stranded fish from the exposed beach. Furthermore, at the coastal town of Kanyakumari, the seabed was exposed briefly before a large wall of water can be seen on the horizon and subsequently flooding the town. Other footage showed the tsunami dramatically crashed into the Vivekananda Rock Memorial. [78] The worst affected area in Tamil Nadu was Nagapattinam district, with 6,051 fatalities caused by a 5 m (16 ft) tsunami, followed by Cuddalore district, with many villages destroyed. [78] Most of the people killed were members of the fishing community. [78]

The state of Kerala experienced tsunami-related damage in three southern densely populated districts, Ernakulam, Alappuzha, and Kollam, due to diffraction of the waves around Sri Lanka. The southernmost district of Thiruvananthpuram, however, escaped damage, possibly due to the wide turn of the diffracted waves at the peninsular tip. Major damage occurred in two narrow strips of land bound on the west by the Arabian Sea and on the east by the Kerala backwaters. The waves receded before the first tsunami with the highest fatality reported from the densely populated Alappad panchayat (including the villages of Cheriya Azhikkal and Azhikkal) at Kollam district, caused by a 4 m (13 ft) tsunami. [78] A video recorded by locals showed the tsunami flooding the beach and villages causing despair amongst the villagers.

Many villages in the state of Andhra Pradesh were destroyed. In the Krishna district, the tsunami created havoc in Manginapudi and on Machalipattanam Beach. The most affected was Prakasham District, recording 35 deaths, with maximum damage at Singraikonda. [78] Given the enormous power of the tsunami, the fishing industry suffered the greatest. Moreover, the cost of damage in the transport sector was reported in the tens of thousands. [78]

The tsunami run-up was only 1.6 m (5.2 ft) in areas in the state of Tamil Nadu shielded by the island of Sri Lanka but was 4–5 m (13–16 ft) in coastal districts such as Nagapattinam in Tamil Nadu directly across from Sumatra. On the western coast, the runup elevations were 4.5 m (15 ft) at Kanyakumari District in Tamil Nadu and 3.4 m (11 ft) each at Kollam and Ernakulam districts in Kerala. The time between the waves ranged from about 15 minutes to 90 minutes. [75] [77] [79] The tsunami varied in height from 2 m (6.6 ft) to 10 m (33 ft) based on survivors' accounts. [78] The tsunami travelled 2.5 km (1.6 mi) at its maximum inland at Karaikal, Puducherry. [78] The inundation distance varied between 1,006–500 m (3,301–1,640 ft) in most areas, except at river mouths, where it was more than 1 km (0.62 mi). Areas with dense coconut groves or mangroves had much smaller inundation distances, and those with river mouths or backwaters saw larger inundation distances. [ citation needed ] Presence of seawalls at the Kerala and Tamil Nadu coasts reduced the impact of the waves. However, when the seawalls were made of loose stones, the stones were displaced and carried a few metres inland. [75] [77] [79]

Andaman and Nicobar Islands

Due to close proximity to the earthquake, the tsunami took just minutes to devastate the Andaman and Nicobar Islands. The Andaman Islands were moderately affected while the island of Little Andaman and the Nicobar Islands were severely affected by the tsunami.

In South Andaman island, based on local eyewitnesses, there were three tsunami waves, with the third being the most destructive. Flooding occurred at the coast and low-lying areas inland, which were connected to open sea through creeks. Inundation was observed, along the east coast of South Andaman Island, restricted to Chidiyatapu, Burmanallah, Kodiaghat, Beadnabad, Corbyn's cove and Marina Park/Aberdeen Jetty areas. Along the west coast, the inundation was observed around Guptapara, Manjeri, Wandoor, Collinpur and Tirur regions. Several near-shore establishments and numerous infrastructures such as seawalls and a 20 MW diesel-generated power plant at Bamboo Flat were destroyed. [80] At Port Blair, the water receded before the first wave, and the third wave was the tallest and caused the most damage.

Results of the tsunami survey in South Andaman along Chiriyatapu, Corbyn's Cove and Wandoor beaches: [ citation needed ]

  • 5 m (16 ft) in maximum tsunami height with a run-up of 4.24 m (13.9 ft) at Chiriyatapu Beach
  • 5.5 m (18 ft) in maximum tsunami height and run-up at Corbyn's Cove Beach
  • 6.6 m (22 ft) in maximum tsunami height and run-up of 4.63 m (15.2 ft) at Wandoor Beach

Meanwhile, in the Little Andaman, tsunami waves impinged on the eastern shore about 25 to 30 minutes after the earthquake in a four-wave cycle of which the fourth tsunami was the most devastating with a wave height of about 10 m (33 ft). The tsunami destroyed settlements at Hut Bay within a range of 1 km (0.62 mi) from the seashore. Run up level up to 3.8 m (12 ft) have been measured. [80]

In Malacca, located on the island of Car Nicobar, there were three tsunami waves. The sea was observed to rise suddenly before the onset of the first wave. The first wave came 5 minutes after the earthquake, preceded by a recession of the sea up to 600–700 m (2,000–2,300 ft). [ citation needed ] . The second and third waves came in 10 minutes intervals after the first wave. The third wave was the strongest, with a maximum tsunami wave height of 11 m (36 ft). Waves nearly three stories high devastated the Indian Air Force base, located just south of Malacca. The maximum tsunami wave height of 11 m (36 ft). [ citation needed ] Inundation limit was found to be up to 1.25 km (0.78 mi) inland. The impact of the waves was so severe that four oil tankers were thrown almost 800 m (2,600 ft) from the seashore near Malacca to the Air force colony main gate. [80] In Chuckchucha and Lapati, the tsunami arrived in a three-wave cycle with a maximum tsunami wave height of 12 m (39 ft).

In Campbell Bay of Great Nicobar Island, the tsunami waves hit the area three times with an inundation limit of 250–500 m (820–1,640 ft). A rise in sea level was observed before the first wave came within 5 minutes of the earthquake. The second and third waves came in 10-minute intervals after the first. The second wave was the strongest. The tsunami waves wreaked havoc in the densely populated Jogindar Nagar area, situated 13 km (8.1 mi) south of Campbell Bay. [ citation needed ] According to local accounts, [ attribution needed ] tsunami waves attacked the area three times. The first wave came five minutes after the mainshock (0629 hrs.) with a marginal drop in sea level. The second wave came 10 minutes after the first one with a maximum height of 4.8 m (16 ft) to 8 m (26 ft) and caused the major destruction. The third wave came within 15 minutes after the second with lower wave height. The maximum inundation limit due to tsunami water was about 500 m (1,600 ft). [80]

The worst affected island in the Andaman & Nicobar chain is Katchall Island, with 303 people confirmed dead and 4,354 missing out of a total population of 5,312. [81] [82] [83] The significant shielding of Port Blair and Campbell Bay by steep mountainous outcrops contributed to the relatively low wave heights at these locations, whereas the open terrain along the eastern coast at Malacca and Hut Bay contributed to the great height of the tsunami waves. [82] [84]

Reports of tsunami wave height: [85] [86]

  • 1.5 m (4 ft 11 in) at Diglipur and Rangat at North Andaman Island
  • 8 m (26 ft) high at Campbell Bay on Great Nicobar Island
  • 10–12 m (33–39 ft) high at Malacca (in Car Nicobar Island) and at Hut Bay on Little Andaman Island
  • 3 m (9.8 ft) high at Port Blair on South Andaman Island

Maldives

The tsunami severely affected the Maldives at a distance of 2,500 km (1,600 mi) from the epicentre. Similar to Sri Lanka, survivors reported three waves with the second wave being the most powerful. Being rich in coral reefs, the Maldives provides an opportunity for scientists to assess the impact of a tsunami on coral atolls. The significantly lower tsunami impact on the Maldives compared to Sri Lanka is mostly due to the topography and bathymetry of the atoll chain with offshore coral reefs, deep channels separating individual atolls and its arrival within low tide which decreased the power of the tsunami. After the tsunami, there was some concern that the country might be submerged entirely and become uninhabitable. However, this was proven untrue. The highest tsunami wave measured was 4 m (13 ft) at Vilufushi Island. The tsunami arrived approximately 2 hours after the earthquake. The greatest tsunami inundation occurred at North Male Atoll, Male island at 250 m (820 ft) along the streets.

Local footage recorded showed the tsunami flooding the streets up to knee level in town, while another video taken at the beach showed the tsunami slowly flooding and gradually surging inland.

The Maldives tsunami wave analysis:

  • 1.3–2.4 m (4 ft 3 in–7 ft 10 in) at North Male Atoll, Male Island
  • 2 m (6 ft 7 in) at North Male Atoll, Huhule Island
  • 1.7–2.8 m (5 ft 7 in–9 ft 2 in) at South Male Atoll, Embudhu Finothu
  • 2.5–3.3 m (8 ft 2 in–10 ft 10 in) at Laamu Atoll, Fonadhoo Island
  • 2.2–2.9 m (7 ft 3 in–9 ft 6 in) at Laamu Atoll, Gan Island
  • 2.3–3 m (7 ft 7 in–9 ft 10 in) at North Male Atoll, Dhiffushi Island
  • 2.2–2.4 m (7 ft 3 in–7 ft 10 in) at North Male Atoll, Huraa Island
  • more than 1.5 m (4 ft 11 in) at North Male Atoll, Kuda Huraa Island

Myanmar

In Myanmar, the tsunami caused only moderate damage, which arrived between 2 and 5.5 hours after the earthquake. Although the country's western Andaman Sea coastline lies at the proximity of the rupture zone, there were smaller tsunamis than the neighbouring Thai coast, because the main tsunami source did not extend to the Andaman Islands. Another factor is that some coasts of Taninthayi Division were protected by the Myeik Archipelago. Based on scientific surveys from Ayeyarwaddy Delta through Taninthayi Division, it was revealed that tsunami heights along the Myanmar coast were between 0.4–2.9 m (1 ft 4 in–9 ft 6 in). Eyewitnesses compared the tsunami with the "rainy-season high tide" although at most locations, the tsunami height was similar or smaller than the "rainy-season high tide" level. [87]

Tsunami survey heights: [ citation needed ]

  • 0.6–2.3 m (2 ft 0 in–7 ft 7 in) around the Ayeyarwady delta
  • 0.9–2.9 m (2 ft 11 in–9 ft 6 in) at Dawei area
  • 0.7–2.2 m (2 ft 4 in–7 ft 3 in) around Myeik
  • 0.4–2.6 m (1 ft 4 in–8 ft 6 in) around Kawthaung

Interviews with local people indicate that they did not feel the earthquake in Taninthayi Division or Ayeyarwaddy Delta. The 71 casualties can be attributed to poor housing infrastructure and additionally, the fact that the coastal residents in the surveyed areas live on flat land along the coast, especially in the Ayeyarwaddy Delta, and that there is no higher ground to which to evacuate. The tsunami heights from the 2004 December earthquake were not more than 3 m (9.8 ft) along the Myanmar coast, the amplitudes were slightly large off the Ayeyarwaddy Delta, probably because the shallow delta caused a concentration in tsunami energy. [87]

Somalia

The tsunami travelled 5,000 km (3,100 mi) west across the open ocean before striking the East African country of Somalia. Around 289 fatalities were reported in the Horn of Africa, drowned by four tsunami waves. The hardest-hit was a 650 km (400 mi) stretch of the Somalia coastline between Garacad (Mudug region) and Xaafuun (Bari region), which forms part of the Puntland province. Most of the victims were reported along the low-lying Xaafuun Peninsula. [88] The Puntland coast in northern Somalia was by far the area hardest hit by the waves to the west of the Indian subcontinent. The waves arrived around noon local time. [88]

Consequently, tsunami runup heights vary from 5 m (16 ft) to 9 m (30 ft) with inundation distances varying from 44 m (144 ft) to 704 m (2,310 ft). The maximum runup height of almost 9 m (30 ft) was recorded in Bandarbeyla. An even higher runup point was measured on a cliff near the town of Eyl, solely on an eyewitness account.

The highest death toll was in Hafun, with 19 dead and 160 people presumed missing out of its 5,000 inhabitants. This was the highest number of casualties in a single African town and the largest tsunami death toll in a single town to the west of the Indian subcontinent. In Xaafuun, small drawbacks were observed before the third and most powerful tsunami wave flooded the town. [88]

Other locations

The tsunami also reached Malaysia, mainly on the northern states such as Kedah, Perak and Penang and on offshore islands such as Langkawi island. Peninsular Malaysia was shielded by the full force of the tsunami due to the protection offered by the island of Sumatra, which lies just off the western coast. [89]

Bangladesh escaped major damage and deaths because the water displaced by the strike-slip fault was relatively little on the northern section of the rupture zone, which ruptured slowly. In Yemen, the tsunami killed two people with a maximum runup of 2 m (6.6 ft). [90]

The tsunami was detected in the southern parts of east Africa, where rough seas were reported, specifically on the eastern and southern coasts that face the Indian Ocean. A few other African countries also recorded fatalities one in Kenya, three in Seychelles, ten in Tanzania, and South Africa, where two were killed as a direct result of the tsunami—the furthest from the epicentre. [91] [92]

Tidal surges also occurred along the Western Australian coast that lasted for several hours, resulting in boats losing their moorings and two people needing to be rescued. [93]

Countries affected

According to the U.S. Geological Survey, a total of 227,898 people died. [1] Measured in lives lost, this is one of the ten worst earthquakes in recorded history, as well as the single worst tsunami in history. Indonesia was the worst affected area, with most death toll estimates at around 170,000. [94] An initial report by Siti Fadilah Supari, the Indonesian Minister of Health at the time, estimated the death total to be as high as 220,000 in Indonesia alone, giving a total of 280,000 fatalities. [95] However, the estimated number of dead and missing in Indonesia were later reduced by over 50,000. In their report, the Tsunami Evaluation Coalition stated, "It should be remembered that all such data are subject to error, as data on missing persons especially are not always as good as one might wish". [6] A much higher number of deaths has been suggested for Myanmar based on reports from Thailand. [96]

The tsunami caused severe damage and deaths as far as the east coast of Africa, with the furthest recorded fatality directly attributed to the tsunami at Rooi-Els, close to Cape Town, 8,000 km (5,000 mi) from the epicentre. In total, eight people in South Africa died due to high sea levels and waves. [ citation needed ]

Relief agencies reported that one third of the dead appeared to be children. This was a result of the high proportion of children in the populations of many of the affected regions and because children were the least able to resist being overcome by the surging waters. Oxfam went on to report that as many as four times more women than men were killed in some regions because they were waiting on the beach for the fishers to return and looking after their children in the houses. [97]

States of emergency were declared in Sri Lanka, Indonesia, and the Maldives. The United Nations estimated at the outset that the relief operation would be the costliest in human history. [ citation needed ] Then-UN Secretary-General Kofi Annan stated that reconstruction would probably take between five and ten years. Governments and non-governmental organizations feared that the final death toll might double as a result of diseases, prompting a massive humanitarian response. [ citation needed ]

In addition to a large number of local residents, up to 9,000 foreign tourists (mostly Europeans) enjoying the peak holiday travel season were among the dead or missing, especially people from the Nordic countries. [98] The European nation hardest hit was Sweden, with a death toll of 543. Germany was close behind with 539 identified victims.

  • ^a This table refers only to countries directly affected by the tsunami, not to countries whose citizens were affected while overseas.
  • ^b Includes those reported under 'Confirmed'. If no separate estimates are available, the number in this column is the same as reported under 'Confirmed'.
  • ^c Does not include approximately 19,000 missing people initially declared by Tamil Tiger authorities from regions under their control.
  • ^d Data includes at least 2,464 foreigners.
  • ^e Does not include South African citizens who died outside of South Africa (e.g., tourists in Thailand).

Economic impact

The level of damage to the economy resulting from the tsunami depends on the scale examined. While local economies were devastated, the overall impact on the national economies was minor. The two main occupations affected by the tsunami were fishing and tourism. [116] The impact on coastal fishing communities and the people living there, some of the poorest in the region, has been devastating with high losses of income earners as well as boats and fishing gear. [117] [118] In Sri Lanka artisanal fishery, where the use of fish baskets, fishing traps, and spears are commonly used, is an important source of fish for local markets industrial fishery is the major economic activity, providing direct employment to about 250,000 people. In recent years the fishery industry has emerged as a dynamic export-oriented sector, generating substantial foreign exchange earnings. Preliminary estimates indicate that 66% of the fishing fleet and industrial infrastructure in coastal regions have been destroyed by the wave surges, which will have adverse economic effects both at local and national levels. [119]

While the tsunami destroyed many of the boats vital to Sri Lanka's fishing industry, it also created a demand for fibreglass reinforced plastic catamarans in boatyards of Tamil Nadu. Since over 51,000 vessels were lost to the tsunami, the industry boomed. However, the huge demand has led to lower quality in the process, and some important materials were sacrificed to cut prices for those who were impoverished by the tsunami. [120]

Some economists believe that damage to the affected national economies will be minor because losses in the tourism and fishing industries are a relatively small percentage of the GDP. However, others caution that damage to infrastructure is an overriding factor. In some areas drinking water supplies and farm fields may have been contaminated for years by saltwater from the ocean. [121] Even though only coastal regions were directly affected by the waters of the tsunami, the indirect effects have spread to inland provinces as well. Since the media coverage of the event was so extensive, many tourists cancelled vacations and trips to that part of the world, even though their travel destinations may not have been affected. This ripple effect could especially be felt in the inland provinces of Thailand, such as Krabi, which acted as a starting point for many other tourist destinations in Thailand. [122]

Both the earthquake and the tsunami may have affected shipping in the Malacca Straits, which separate Malaysia and the Indonesian island of Sumatra, by changing the depth of the seabed and by disturbing navigational buoys and old shipwrecks. In one area of the Strait, water depths were previously up to 1,200 m (4,000 ft), and are now only 30 m (100 ft) in some areas, making shipping impossible and dangerous. These problems also made the delivery of relief aid more challenging. Compiling new navigational charts may take months or years. However, officials hope that piracy in the region will drop off as a result of the tsunami. [123]

Countries in the region appealed to tourists to return, pointing out that most tourist infrastructure is undamaged. However, tourists were reluctant to do so for psychological reasons. Even beach resorts in parts of Thailand which were untouched by the tsunami were hit by cancellations. [124]

Environmental impact

Beyond the heavy toll on human lives, the Indian Ocean earthquake has caused an enormous environmental impact that will affect the region for many years to come. It has been reported that severe damage has been inflicted on ecosystems such as mangroves, coral reefs, forests, coastal wetlands, vegetation, sand dunes and rock formations, animal and plant biodiversity and groundwater. Also, the spread of solid and liquid waste and industrial chemicals, water pollution and the destruction of sewage collectors and treatment plants threaten the environment even further, in untold ways. The environmental impact will take a long time and significant resources to assess. [125]

According to specialists, the main effect is being caused by poisoning of the freshwater supplies and of the soil by saltwater infiltration and a deposit of a salt layer over arable land. It has been reported that in the Maldives, 16 to 17 coral reef atolls that were overcome by sea waves are without fresh water and could be rendered uninhabitable for decades. Uncountable wells that served communities were invaded by sea, sand, and earth and aquifers were invaded through porous rock. Salted-over soil becomes sterile, and it is difficult and costly to restore for agriculture. It also causes the death of plants and important soil micro-organisms. Thousands of rice, mango, and banana plantations in Sri Lanka were destroyed almost entirely and will take years to recover. On the island's east coast, the tsunami contaminated wells on which many villagers relied for drinking water. The Colombo-based International Water Management Institute monitored the effects of saltwater and concluded that the wells recovered to pre-tsunami drinking water quality one-and-a-half years after the event. [126] The IWMI developed protocols for cleaning wells contaminated by saltwater these were subsequently officially endorsed by the World Health Organization as part of its series of Emergency Guidelines. [127]

The United Nations Environment Programme (UNEP) is working with governments of the region in order to determine the severity of the ecological impact and how to address it. [ needs update ] [128] UNEP has decided to earmark a US$1 million emergency fund and to establish a Task Force to respond to requests for technical assistance from countries affected by the tsunami. [129] In response to a request from the Maldivian Government, the Australian Government sent ecological experts to help restore marine environments and coral reefs—the lifeblood of Maldivian tourism. Much of the ecological expertise has been rendered from work with the Great Barrier Reef, in Australia's northeastern waters.

Historical context

The last major tsunami in the Indian Ocean was about A.D. 1400. [130] [131] In 2008, a team of scientists working on Phra Thong, a barrier island along the hard-hit west coast of Thailand, reported evidence of at least three previous major tsunamis in the preceding 2,800 years, the most recent from about 700 years ago. A second team found similar evidence of previous tsunamis in Aceh, a province at the northern tip of Sumatra radiocarbon dating of bark fragments in the soil below the second sand layer led the scientists to estimate that the most recent predecessor to the 2004 tsunami probably occurred between A.D. 1300 and 1450. [132]

The 2004 earthquake and tsunami combined is the world's deadliest natural disaster since the 1976 Tangshan earthquake. The earthquake was the third-most-powerful earthquake recorded since 1900. The deadliest-known earthquake in history occurred in 1556 in Shaanxi, China, with an estimated death toll of 830,000, though figures from this period may not be as reliable. [133]

Before 2004, the tsunami created in both Indian and Pacific Ocean waters by the 1883 eruption of Krakatoa, thought to have resulted in anywhere from 36,000 to 120,000 deaths, had probably been the deadliest in the region. In 1782, about 40,000 people are thought to have been killed by a tsunami (or a cyclone) in the South China Sea. [134] The deadliest tsunami before 2004 was Italy's 1908 Messina earthquake on the Mediterranean Sea where the earthquake and tsunami killed about 123,000. [135]

Other effects

Many health professionals and aid workers have reported widespread psychological trauma associated with the tsunami. [136] Traditional beliefs in many of the affected regions state that a relative of the family must bury the body of the dead, and in many cases, no body remained to be buried. Women in Aceh required a special approach from foreign aid agencies, and continue to have unique needs. [ citation needed ]

The hardest-hit area, Aceh, is a religiously conservative Islamic society and has had no tourism nor any Western presence in recent years due to the insurgency between the Indonesian military and Free Aceh Movement (GAM). Some believe that the tsunami was divine punishment for lay Muslims shirking their daily prayers or following a materialistic lifestyle. Others have said that Allah was angry that Muslims were killing each other in an ongoing conflict. [137] Saudi cleric Muhammad Al-Munajjid attributed it to divine retribution against non-Muslim vacationers "who used to sprawl all over the beaches and in pubs overflowing with wine" during Christmas break. [138]

The widespread devastation caused by the tsunami led GAM to declare a cease-fire on 28 December 2004 followed by the Indonesian government, and the two groups resumed long-stalled peace talks, which resulted in a peace agreement signed 15 August 2005. The agreement explicitly cites the tsunami as a justification. [139]

In a poll conducted in 27 countries, 15% of respondents named the tsunami the most significant event of the year. Only the Iraq War was named by as many respondents. [140] [141] The extensive international media coverage of the tsunami, and the role of mass media and journalists in reconstruction, were discussed by editors of newspapers and broadcast media in tsunami-affected areas, in special video-conferences set up by the Asia Pacific Journalism Centre. [142]

The tsunami left both the people and government of India in a state of heightened alert. On 30 December 2004, four days after the tsunami, Terra Research notified the India government that its sensors indicated there was a possibility of 7.9 to 8.1 magnitude tectonic shift in the next 12 hours between Sumatra and New Zealand. [143] In response, the Indian Minister of Home Affairs announced that a fresh onslaught of deadly tsunami was likely along the southern Indian coast and the Andaman and Nicobar Islands, even as there was no sign of turbulence in the region. [143] The announcement generated panic in the Indian Ocean region and caused thousands to flee their homes, which resulted in jammed roads. [144] The announcement was a false alarm, and the Home Affairs minister withdrew their announcement. [144] On further investigation, the India government learned that the consulting company Terra Research was run from the home of a self-described earthquake forecaster who had no telephone listing and maintained a website where he sold copies of his detection system. [145]

The tsunami had a severe humanitarian and political impact in Sweden. The hardest-hit country outside Asia, Sweden, lost 543 tourists, mainly in Thailand. The Persson Cabinet was heavily criticized for its inaction. [146]

Smith Dharmasaroja, a meteorologist who had predicted that an earthquake and tsunami "is going to occur for sure" way back in 1994, [147] [148] was assigned the development of the Thai tsunami warning system. The Indian Ocean Tsunami warning system was formed in early 2005 to provide an early warning of tsunamis for inhabitants around the Indian Ocean coasts. [149]

The changes in the distribution of masses inside the Earth due to the earthquake had several consequences. It displaced the North Pole by 25 mm (0.98 in). It also slightly changed the shape of the Earth, specifically by decreasing Earth's oblateness by about one part in 10 billion, consequentially increasing Earth's rotation a little and thus shortening the length of the day by 2.68 microseconds. [150]

A great deal of humanitarian aid was needed because of widespread damage to the infrastructure, shortages of food and water, and economic damage. Epidemics were of particular concern due to the high population density and tropical climate of the affected areas. The main concern of humanitarian and government agencies was to provide sanitation facilities and fresh drinking water to contain the spread of diseases such as cholera, diphtheria, dysentery, typhoid and hepatitis A and hepatitis B .

There was also a great concern that the death toll could increase as disease and hunger spread. However, because of the initial quick response, this was minimized. [151]

In the days following the tsunami, significant effort was spent in burying bodies hurriedly due to fear of disease spreading. However, the public health risks may have been exaggerated, and therefore this may not have been the best way to allocate resources. The World Food Programme provided food aid to more than 1.3 million people affected by the tsunami. [152]

Nations all over the world provided over US$14 billion in aid for damaged regions, [153] with the governments of Australia pledging US$819.9 million (including a US$760.6 million aid package for Indonesia), Germany offering US$660 million, Japan offering US$500 million, Canada offering US$343 million, Norway and the Netherlands offering both US$183 million, the United States offering US$35 million initially (increased to US$350 million), and the World Bank offering US$250 million. Also, Italy offered US$95 million, increased later to US$113 million of which US$42 million was donated by the population using the SMS system [154] Four countries, Australia, India, Japan and the United States formed an ad-hoc corroborative group, and it was the origin of Quadrilateral Security Dialogue. [155]

According to USAID, the US has pledged additional funds in long-term U.S. support to help the tsunami victims rebuild their lives. On 9 February 2005, President Bush asked Congress to increase the U.S. commitment to a total of US$950 million. Officials estimated that billions of dollars would be needed. Bush also asked his father, former President George H. W. Bush, and former President Bill Clinton to lead a U.S. effort to provide private aid to the tsunami victims. [156]

In mid-March, the Asian Development Bank reported that over US$4 billion in aid promised by governments was behind schedule. Sri Lanka reported that it had received no foreign government aid, while foreign individuals had been generous. [157] Many charities were given considerable donations from the public. For example, in the United Kingdom, the public donated roughly £330 million sterling (nearly US$600 million). This considerably outweighed the allocation by the government to disaster relief and reconstruction of £75 million and came to an average of about £5.50 (US$10) donated by every citizen. [158] [159]

In August 2006, fifteen local aid staff working on post-tsunami rebuilding were found executed in north-east Sri Lanka after heavy fighting, the main umbrella body for aid agencies in the country said. [160]


On the Hunt for Tsunamis

Have large, devastating tsunamis ever hit Orange County’s and surrounding Southern California coastal areas? Not in recent times.

But perhaps thousands of years ago, say geologists Matthew E. Kirby and Brady P. Rhodes, who are conducting a pilot study to hunt for geological signs in sediment preserved in Southern California's wetlands to determine the region's tsunami history.

Caption: Brady Rhodes

“We’re trying to find evidence of past tsunamis,” said Rhodes, professor of geological sciences. “No written historical records exist in Southern California of any significant tsunamis affecting our coast. Historical written records extend back only 150 to 200 years.”

Scientists have used computerized, theoretical models to show that large tsunamis could have happened, said Kirby, associate professor of geological sciences. “So we’re saying, ‘Let’s go looking for them let’s get some real geological evidence.’”

Caption: Matthew Kirby

The researchers recently received a $57,700 National Science Foundation Early-Concept Grant for Exploratory Research for “Search for a Paleotsunami Record in the Wetlands of California.” The study will include wetlands between Santa Barbara and the Mexican border, including Orange County.

The geologists have enlisted geology graduate and undergraduate students to assist them, including Fulbright scholar Khadija Nadimi from Pakistan, who holds a master's degree in geophysics and is working on a master’s in geology. Scientists from the U.S. Geologic Survey and the California Geologic Survey also are collaborating on the project.

If they find evidence of large tsunamis, “We’ll need more funding to do much study beyond this exploratory project,” Rhodes said.

Exploring Tsunamis History

Tsunami research is not new to the faculty members. Rhodes is a structural geologist whose expertise now includes tsunami geology, and Kirby studies prehistoric climate trends and sedimentology. For several years, both have traveled to Thailand to conduct tsunami research.

“We’re bringing our research experience from Thailand to Southern California,” said Rhodes. Currently, the pair is working on analyzing sediment samples from Thailand, in order to establish the history of tsunamis in the Indian Ocean.

In 2004, a 9.3 magnitude earthquake in the Indian Ocean off Sumatra triggered a tsunami that devastated the country and killed more than 220,000 people. Last year, a smaller magnitude 9.0 earthquake off the densely populated east coast of Japan triggered a tsunami of similar size, but with a much lower death toll. The reason, said Rhodes, is that Japan has a rich record, both geological and historical, of past tsunamis, providing important information that helped the country be better prepared.

Being more aware and equipped is the reason for Kirby and Rhodes’ research, which they say is not “doomsday science,” but a project that needs to be done and would potentially allow scientists to look back several thousand years into the past for evidence of tsunamis.

Southern California’s coastal wetlands were formed during the Holocene Epoch, the period between approximately 12,000 years ago and present day when the sea level rose from huge amounts of ice melting at the end of the last ice age. That period provided an ideal, predominantly muddy sedimentary environment to capture a sandy tsunami deposit, Rhodes said.

Finding a record of tsunamis in Southern California will verify and validate much of the research over the last decade on computer modeling of local tsunamis from underwater landslides and offshore earthquakes, Kirby explained.

Study’s Importance

The significance of their exploratory research is potentially far-reaching, said the researchers. Southern California’s densely populated coastal zone is home to three large ports, including the Port of Los Angeles and Long Beach Harbor, as well as 10 power plants, including the San Onofre nuclear power plant in Orange County.

“Even a modestly sized tsunami would have an enormous impact on the economy and people of Southern California,” Kirby said.

A geologic record of tsunamis would represent a “transformative scientific discovery that would help verify the occurrence, scale and frequency of inundation — critical information for planning tsunami hazard mitigation,” the geologists noted.

“Knowledge of our own tsunami history would help us prepare for the next one,” Kirby said.

Tsunami warnings, like this one at Orange County’s Sunset Beach, have been posted along California coastal cities since the destructive 2004 Indian Ocean tsunami killed more than 200,000 people.


India and Day 26 – Part 3: The Devastating Indian Ocean Tsunami

On Sunday, December 26, 2004, an undersea megathrust earthquake, known as the Sumatra–Andaman earthquake occurred at 00:58:53 UTC in the Indian Ocean with an epicentre off the west coast of Sumatra, between Simeulue in the Aceh province of Indonesia and mainland Indonesia. The earthquake with a magnitude of M w 9.1–9.3, is the third largest earthquake ever recorded on a seismograph.

The duration of faulting, between 8.3 and 10 minutes, was the longest ever observed. The behemothic quake caused the entire planet to vibrate as much as 1 centimetre (0.4 inches) and triggered other minor earthquakes as far away as Alaska.

The tsunami was then known by various other names such as: “The 2004 Indian Ocean tsunami,” “South Asian tsunami,” and “Indonesian tsunami.” Since the tsunami occurred on December 26, it was also known as the “Christmas tsunami” and the “Boxing Day tsunami.”

December 26, 2004 Indian Ocean Tsunami. (Source: all-that-is-interesting.com)

The earthquake triggered a tsunami, considered to be one of the deadliest in history, which inundated coastal communities with waves up to 100 feet (30 meters) high and killed over 230,000 people in fourteen countries. It was one of the deadliest natural disasters in recorded history.

Coastlines severely hit by the December 26, 2004 tsunami (Source: academic.evergree.edu)

The huge waves racing at the speed of a jet aircraft took fifteen minutes to seven hours to reach the various coastlines. The waves hit the northern regions of the Indonesian island of Sumatra immediately. Thailand was struck about two hours later, despite being closer to the epicentre because the tsunami waves travelled more slowly in the shallow Andaman Sea off its western coast. About an hour and a half to two hours after the quake, Sri Lanka and the east coast of India were hit. The waves then reached the Maldives.

Indonesia was the hardest-hit country, followed by Sri Lanka, India, and Thailand.

The earthquake and resulting tsunami in the Indian Ocean had a devastating effect on India. According to the Ministry of Home Affairs about 18,000 are estimated dead.

The following table compiled by the U.S. Geological Survey shows that a total of 227,898 people died. According to this table, in mainland India and in its territories, the Andaman and Nicobar Islands, 12,405 people died in the tsunami, around 5,640 are missing and 647,599 people have been displaced.

Figures compiled by the U.S. Geological Survey.

The Andaman and Nicobar Islands in the Indian Ocean were devastated by the tsunami, and by the initial quake and several aftershocks that occurred during the following days. The Great Nicobar and Car Nicobar islands were the worst hit among all the islands due to their proximity to the epicentre of the quake and because of the relatively flat terrain.

One-fifth of the population in Nicobar Islands was reported dead, missing or wounded. Chowra Island lost two-thirds of its population of 1,500. Communication was cut off when many islands submerged. The Trinket Island was bifurcated.

Fishing communities were destroyed and very little is known about the effects of the tsunami on the indigenous tribes of the Andaman and Nicobar islands.

The official death toll in the Andaman and Nicobar Islands was 1,310, with about 5,600 missing from the islands. But the unofficial death toll, including those missing and presumed dead, was estimated to be around 7,000.

Map showing Tsunami Affected Areas in India.

The tsunami hit the southeastern regions of the Indian mainland. It inundated villages and devastated cities along the coast. Around 8,000 deaths were reported from Tamilnadu, and around 200 deaths from Kerala. The district of Nagapattinam was the worst hit in Tamil Nadu, with nearly 5,500 deaths.

The tsunami of December 26, 2004 inundated villages and devastated cities along the coast of southeastern regions of the Indian mainland. Crown. (Source: indyas.hpage.co.in)

Surprisingly, Bangladesh, which lies at the northern end of the Bay of Bengal, had only two confirmed deaths, despite being a low-lying country and located relatively near the epicenter. Also, distance alone does not guarantee a safety since Somalia located in the Horn of Africa on the eastern coast was hit harder than Bangladesh even though it is much farther away.

Coasts, with a landmass between them and the location of origin of a tsunami, are usually deemed safe, but tsunami waves can sometimes steer around such landmasses. Being a relatively small island, the western coast of Sri Lanka suffered substantial damages from the impact of the tsunami likewise, the Indian state of Kerala too was hit by the tsunami, despite being on the western coast of India.

The government of India announced a financial package of about US$200 million to Andaman and Nicobar islands after the tsunami, but the unbearable living conditions due to rise in sea level, constant aftershocks and fear of another similar tsunami, propelled thousands of settlers on the islands to relocate to the Indian mainland.

According to the World Bank, reconstruction was expected to cost more than US$1 . 2 billion in India alone.


10 years after the Indian Ocean Tsunami: What have we learned?

Professor Phil Cummins is an earthquake seismologist whose research focuses on earthquake and tsunami hazard, the rupture properties of subduction zone earthquakes, and the active tectonics and crustal structure of Indonesia.

Though no one realised it at the time, the 2004 Sumatra-Andaman earthquake was the first in a series of massive earthquakes to shake the globe. At magnitude 9.1 it is among the three largest earthquakes ever recorded since instrumental recordings began at the turn of the 20th century. The following seven years saw the occurrence of another three of the ten largest earthquakes ever recorded (including the giant earthquake and tsunami in northeast Japan in 2011). This sequence of four megaquakes occurring over 2004-11 rivals another series that occurred over 1952-1965, when another four of the ten largest earthquakes ever recorded occurred around the Pacific Rim - including a magnitude 9.5 offshore Chile in 1960 - the largest earthquake ever recorded.

We still know very little about why megaquakes occur in clusters like this. One explanation for the recent large events is the mechanism of stress transfer, in which the Sumatra subduction zone 'unzipped' in a series of massive earthquakes that ruptured sequentially from northwest to southeast from 2004-07. But this does not explain the presence of a large 'gap' in central Sumatra. In this section the recurrence of earthquakes that occurred in 1797 and 1833 was - and still is - widely anticipated, not only by scientists but by the many residents of the city of Padang, who are crowded into a low-lying coastal strip that will almost certainly be inundated by the resulting tsunami. However, the 'unzipping' of the subduction zone mysteriously skipped this segment during the 2004-07 sequence. Likewise, we don't know what role, if any, the 2004 Sumatra Andaman earthquake may have played in triggering distant events like the 2010 Maule, Chile and the 2011 Tohoku, Japan earthquakes. And we don't know if the present sequence of megaquakes is at an end.

What we do know is that the 2004 Sumatra Andaman earthquake generated a massive tsunami - the Indian Ocean Tsunami - that killed over 227 000 people, more than ten times the number of lives lost in the remaining nine of the ten largest earthquakes combined (the total fatalities for these was about 21 000). Why did the Indian Ocean Tsunami kill so many compared to other earthquakes of similar size? First, the earthquake occurred just offshore of a major population centre. The population of Banda Aceh before the tsunami was over 264 000, and these in addition to the populations of towns along the western coast of Aceh were severely affected by the tsunami. The town of Lhok Nga, where observations of tsunami run-up height reached over 30 metres, had a pre-tsunami population of 7000, reduced to 400 after the tsunami. Banda Aceh itself suffered over 61 000 fatalities, almost 25% of its population. In all, Indonesian fatalities are thought to number at least 167 000 (estimates range as high as 220 000), over 70% of the total Indian Ocean Tsunami fatalities. Even when only the Indonesian fatalities are considered, the Indian Ocean Tsunami is the world's deadliest tsunami disaster.

But the Indian Ocean Tsunami was unique among tsunami disasters in the scale of fatalities caused on a regional scale. Because the rupture extended far north from Sumatra into the Andaman Sea, both India and Sri Lanka in the west, and Thailand in the east, were directly in the path of the main plume of tsunami energy. In addition to the 167 000+ fatalities in Indonesia, over 61 000 died in Sri Lanka, India and Thailand. Around 2000 Europeans, many tourists visiting Thailand, were killed, including over 500 each from Sweden and Germany. 26 Australians also died while overseas in southeast Asia, and dozens were swept to sea by the large waves and strong currents generated when the tsunami reached Australia's western coast.

In addition to the large coastal populations exposed to the tsunamis, the major contributing factor to the massive loss of life was a lack of preparedness. A large tsunami in the Indian Ocean was not without historical precedent. The tsunami generated by the eruption of Krakatau in 1883 killed over 35 000 people along the Sunda Strait separating Java and Sumatra. Massive earthquakes in 1797, 1833 and 1861 had occurred off Sumatra, and both the earthquakes and the tsunamis they generated were well documented by Dutch historians. However, these earthquakes had occurred well south of Aceh. While these large local tsunamis destroyed coastal villages, there were at that time no major population centres along this part of the Sumatra coast. The population of Padang, now over 800 000, was only 4000 in 1797. Furthermore, the ruptures of these earthquakes were too far south to have affected Thailand, India and Sri Lanka. So, while there had been large earthquakes and tsunamis in the Indian Ocean, there was no historical precedent for a tsunami affecting large coastal populations. As a consequence there was no warning system, and coastal populations did not know to evacuate low-lying coastal areas in the event of a large earthquake. An exception was the island of Simeulue, to the west of Aceh, where an oral tradition preserved from experience of a smaller tsunami in 1907 caused residents to run to higher ground when they felt the earthquake, saving many lives. In retrospect, it seems clear that better preparedness could have prevented many 10 000s of deaths.

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Much has changed in terms of preparedness in the ten years since the 2004 Indian Ocean Tsunami. A warning system for the Indian Ocean has been established, and many at-risk populations are well aware of the danger of tsunamis, and in many cases are drilled in evacuation procedures. The tsunami risk is taken seriously even in subduction zones that have not historically experienced a megaquake. Were an event like the Indian Ocean Tsunami to occur again today, it seems extremely unlikely that the fatalities caused at regional and greater distances would be anywhere near the scale of the death toll in India, Sri Lanka and Thailand in 2004. This is because, with lead times of several hours between detection of an event and its impact on regional or distant shores, conventional tsunami warning systems are generally very effective.

However, it is important to bear in mind that over 70% of the Indian Ocean Tsunami fatalities, 167 000 or more, were killed by the local tsunami that arrived on the shores of Sumatra within minutes after the earthquake rupture. Local tsunami warning remains a hideously difficult problem, in which decisions must be made and warnings disseminated within minutes, and coastal populations must evacuate within 10s of minutes. This in urban areas that are congested at the best of times, and possibly impassable after suffering the effects of a major earthquake. False alarms are inevitable, and the consequent erosion of public confidence in warning systems are difficult to avoid. Japan's experience of the 2011 Tohoku earthquake and tsunami serves notice that even in the presence of the best warning systems, sophisticated communications and tsunami-aware coastal communities, local tsunamis are still able to inflict massive fatalities. Indonesia and its neighbours can minimise losses by strengthening all these elements of mitigation, but it is still a big challenge to completely avoid high fatality events.

Tsunamis are not the only hazard that can cause massive fatalities. Large as the Indian Ocean Tsunami death toll in Aceh was, there are at least 40 cities in Indonesia larger than Banda Aceh, including the megacity of Jakarta. By virtue of location many of these cities may be relatively sheltered from tsunamis. But they, like many of their cousins in neighbouring countries, have highly concentrated urban populations that typically reside in poorly constructed, masonry homes prone to collapse if subjected to strong earthquake ground motion. Such strong ground motion does not have to come from a megaquake: 316 000 deaths were caused in Port-au-Prince by the 2010 Haiti earthquake, with a magnitude of 'only' 7. Virtually every city in the belt of active tectonics stretching from the Himalayas, through Bangladesh and Burma, Indonesia and the Philippines, as well as much of Papua New Guinea, could potentially experience such an earthquake.

Is a massive-fatality earthquake/tsunami event in the Southeast Asian region inevitable in the 21st century, and if so are mitigation efforts pointless? The explosion in population and urbanisation over the latter half of the 20th century in such a seismically active area would indeed seem to make the eventual occurrence of such a mega-disaster all but certain. So the question then becomes "are mitigation efforts worthwhile"? Absolutely. If the Indian Ocean Tsunami were to occur today, it is likely that the regional warning system would reduce the 61 000 fatalities at regional and greater distance to at most a few thousand. Even if local warning and evacuation procedures were only partially successful, they could reduce fatalities to tens rather than hundreds of thousands. If the effectiveness of tsunami warning systems and community awareness can be maintained over the long term, and if this can be combined with improved building practices, hundreds of thousands - if not millions - of lives can be saved. But we need to draw upon these efforts now, while memories of the Indian Ocean Tsunami are still fresh and it is still possible to channel some of the region's recourses into mitigation efforts. It's the best thing we can do to give meaning to such a devastating natural hazard that changed the lives of so many on that day in 2004.


Watch the video: Documentary: Indian Ocean Earthquake and Tsunami