Acehtsunami

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the earth’s crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium. When large areas of the sea floor elevate or subside, a tsunami can be created.

Large vertical movements of the earth’s crust can occur at plate boundaries. Plates interact along these boundaries called faults. Around the margins of the Pacific Ocean, for example, denser oceanic plates slip under continental plates in a process known as subduction. Subduction earthquakes are particularly effective in generating tsunamis.

Published 15 January 2005 As survivors along the coasts devastated by the tsunami on 26 December 2004 start to clear the debris, the world’s attention is turning to how these communities are going to rebuild their towns and villages. When the unthinkable happens again, will they be any better prepared? ‘When you think of the hundreds of millions of dollars that have been lined up, there is a real chance that we simply rebuild the risky circumstances that we had before,’ warns Reid Basher of the UN’s International Strategy for Disaster Reduction (ISDR) in Bonn, Germany. ‘This is often the case in earthquake situations. The rebuilding reinstates the risk in the big rush to get everything going again.’

But rebuilding also gives communities an opportunity to prepare for future tsunamis, and at little extra cost. The nations that border the Pacific, which are in most danger from earthquake-triggered waves, have pioneered ways to protect themselves. ‘Tsunami defence work consists of political, social, economic, cultural and engineering matters. Not one of them can be neglected,’ says Nobuo Shuto, a tsunami engineer at Iwate Prefectural University in Iwate, Japan.

December 26, 2004
The 2004 Asian Tsunami was a disaster that affected many countries and killed hundreds of thousands of people. At 0:59 GMT on 26 December 2004, the India tectonic plate slid underneath its neighbor the Burma microplate, raising it by about 10 meters. The earthquake caused a powerful tsunami that was one of the deadliest in modern history and devastated coastlines around the Indian Ocean.

The earthquake had a magnitude of 9.0 and was the biggest since the Good Friday Earthquake off Alaska in 1964 which had a magnitude of 9.2. Entire towns were wiped from the map, more than 200,000 people were killed, and millions have been left in urgent need of food and shelter. The epicenter of the earthquake was near the island of Simeulu, off the west coast of Sumatra, Indonesia. The wave hit Indonesia and Thailand within an hour, and then Sri Lanka and India, and eventually reaching as far as eastern Africa. This tsunami destroyed most of the shores of Indonesia, Sri Lanka, South India, Thailand and other places with waves of 15 m (50 ft) high. It caused serious damage and deaths as far as the east coast of Africa

A pair of satellites that happened to be over the Indian Ocean just after the massive Sumatran earthquake on 26 December have captured the only measurements of the tsunamis’ height in deep water. The images will help improve future forecasts of the deadly waves.

The satellites did not observe coastal areas. But for eight minutes, they used radar to measure the sea level along a 3000-kilometre-long track of ocean. This image of the bay as the tsunami rolled through it provides a unique and valuable continuous measure of the waves. In contrast, the floating sensors suggested as part of any future early-warning system can only provide measurements at single points.

The satellites saw the first two wavefronts produced by the main quake, spaced 500 to 800 kilometres apart. These waves reached a maximum height of 50 centimetres in the open ocean, only reaching their full devastating height when entering the shallow waters of the coast.

By comparison, wind-driven waves typically reach 10 metres. However, these waves only involve water close to the ocean surface and are separated by at most several hundred metres.

Tsunami waves have a very deep reach indeed - 4000 metres or more. “These waves involve the entire depth of the ocean. Their energy is thousands of times more than a monster storm, they speed through the water as fast as jet airliners.

The key number in the modelling is wave height in deep water, as this indicates energy, and that is exactly what the radar recorded. Fu adds that, because the waves take time to travel to land, “when you see waves in the open ocean this large, you have time to warn people on the coast

A major earthquake with a moment magnitude of 7.4 (USGS magnitude) occurred at 17:49:39 UTC 15 January 2009 (day 015) and was located 270 miles/432 km south of Severo-Kuril’sk, Kuril Islands, Russia (46.862N, 155.156E, 22.4mi/36.0km depth–USGS location).

This earthquake produced a tsunami that was recorded at tide gages monitored at the Tsunami Warning Centers. Many observatories provide data to the centers; such as the NOAA National Ocean Service, the Japanese Meteorological Agency, the U. of Hawaii Sea Level Center, the Chilean Navy, and the National Tidal Facility in Australia among others. Click on the site name to see a graph of the tsunami, when available. Listed wave heights are maximum amplitude in cm (above sea level). Observed Arrival time is the actual tsunami arrival time in UTC on gages where it could be determined. The Computed Arrival time is the estimated time of arrival computed at the West Coast/Alaska Tsunami Warning Center (WC/ATWC) based on the origin time and location. The Sample Interval column shows the time between samples.

A major earthquake with a moment magnitude of 7.6 (USGS magnitude) occurred at 19:43:55 UTC 3 January (day 003) and was located 93 miles WNW of Manokwari, Irian Jaya, Indonesia (0.51S, 132.787E, 21.7mi/34.7km depth–USGS location).

Two hours and 50 minutes after the first earthquake, a second major earthquake (occurring at 22:33:42 UTC 3 January, 2009) with a moment magnitude of 7.3 (USGS magnitude) occurred 51.7 miles WNW of Manokwari, Irian Jaya, Indonesia (0.695S, 133.279E, 21.7mi/34.7km depth–USGS location).

These earthquakes produced tsunamis that were recorded at tide gages monitored at the Tsunami Warning Centers. Many observatories provide data to the centers; such as the NOAA National Ocean Service, the Japanese Meteorological Agency, the U. of Hawaii Sea Level Center, the Chilean Navy, and the National Tidal Facility in Australia among others. Click on the site name to see a graph of the tsunami, when available. Listed wave heights are maximum amplitude in cm (above sea level). Observed Arrival time is the actual tsunami arrival time in UTC on gages where it could be determined. The Computed Arrival time is the estimated time of arrival computed at the West Coast/Alaska Tsunami Warning Center (WC/ATWC) based on the origin time and location. The Sample Interval column shows the time between samples.

A volcanic eruption, preceded by a swarm of magnitude 3.0 to 5.8 earthquakes, was first observed at 2217 UTC (1417 AKDT) on 07 August 2008, and was located at Kasatochi Volcano - 52.2N, 175.5W.

The Alaska Volcano Observatory (AVO) reported three major explosive eruptions at Kasatochi volcano between approximately 2230 UTC (1430 AKDT) on 07 August and 0500 UTC on 08 August (2100 AKDT on 07 August). Ash from these explosions reached at least 45,000 ft above sea level. According to AVO, the possibility of explosive events continues.

The volcanic eruption produced a 19-cm amplitude tsunami measured at the Adak, Alaska tide gauge at 0324 UTC on 08 August 2008. The tsunami was also recorded at Atka, Alaska with a maximum amplitude of 7 cm. These tide gages are monitored by the Tsunami Warning Centers and are maintained by NOAA�s National Ocean Service. Click on the site name below to see a graph of the tsunami. Listed wave heights are maximum amplitude in cm (above sea level). Observed arrival time is the observed tsunami arrival time in UTC. Approximate tsunami travel times from the volcano to the tide gages are 25 minutes to Adak and 34 minutes to Atka.

A major earthquake with a moment magnitude of 7.3 (USGS magnitude) occurred at 124613 UTC 9 April 2008 (day 100) and was located 70 km SW of Isangel, Tanna, Vanuatu (20.058�S, 168.858�E, 35 km depth - USGS location).

The earthquake produced a tsunami that was recorded at the Port Vila, Vanuatu tide gage monitored at the Tsunami Warning Centers. The data was provided by the National Tidal Facility in Australia. Click on the site name to see a graph of the tsunami. Listed wave heights are maximum amplitude in cm (above sea level). Observed Arrival time is the actual tsunami arrival time in UTC on gages where it could be determined. The Computed Arrival time is the estimated time of arrival computed at the West Coast/Alaska Tsunami Warning Center (WC/ATWC) based on the origin time and location. The Sample Interval column shows the time between samples.

A major earthquake with a moment magnitude of 7.8 (USGS magnitude) occurred at 0728 UTC 12 December 2007 (day 349) and was located south of the Fiji Islands (25.872�S, 177.517�W, 149.2 km depth - USGS location).

The earthquake produced a tsunami that was recorded at the Kings Wharf, Fiji tide gage monitored at the Tsunami Warning Centers. The data was provided by the National Tidal Facility in Australia. Click on the site name to see a graph of the tsunami. Listed wave heights are maximum amplitude in cm (above sea level). Observed Arrival time is the actual tsunami arrival time in UTC on gages where it could be determined. The Computed Arrival time is the estimated time of arrival computed at the West Coast/Alaska Tsunami Warning Center (WC/ATWC) based on the origin time and location. The Sample Interval column shows the time between samples.

A large earthquake with a moment magnitude of 7.7 (USGS magnitude) occurred at 1541 UTC 14 November 2007 (day 318).� The earthquake was located 25 miles/40 km ESE of Tocopilla, Chile (22.2�S, 69.8�W, 25 miles/40 km depth – USGS location).

The earthquake produced a tsunami that was recorded at tide gages monitored at the Tsunami Warning Centers (the tide sites are operated by the Chilean Navy and the National Ocean Service). Click on the site name to see a graph of the tsunami. Listed wave heights are maximum amplitude in cm (above sea level). Observed Arrival time is the actual tsunami arrival time in UTC on gages where it could be determined. The Computed Arrival time is the estimated time of arrival computed at the West Coast/Alaska Tsunami Warning Center (WC/ATWC) based on the origin time and location. The Sample Interval column shows the time between samples.