Tsunami catastrophe which occurred december 2004

Curious beachgoers even wandered out among the oddly receding waves, only to be chased down by a churning wall of water. The death toll in Thailand was nearly 5, including 2, foreign tourists.

An hour later, on the opposite side of the Indian Ocean, the waves struck the southeastern coast of India near the city of Chennai, pushing debris-choked water kilometers inland and killing more than 10, people, mostly women and children, since many of the men were out fishing. But some of the worst devastation was reserved for the island nation of Sri Lanka, where more than 30, people were swept away by the waves and hundreds of thousands left homeless.

He credits the unsparing destructiveness of the Indian Ocean tsunami on the raw power of the earthquake that spawned it. The quake originated in a so-called megathrust fault, where heavy oceanic plates subduct beneath lighter continental plates.

The quake ruptured a mile stretch along the Indian and Australian plates 31 miles below the ocean floor. Rather than delivering one violent jolt, the quake lasted an unrelenting 10 minutes, releasing as much pent-up power as several thousand atomic bombs. In the process, massive segments of the ocean floor were forced upward an estimated 30 or 40 meters up to feet. Titov emphasizes that tsunamis look nothing like the giant surfing break-style waves that many of us imagine.

The effects of extensive thrust faulting carry over to many other microplates nearby, and some local geologic settings are more active than others. The chain of islands sits along the Sunda Trench, which is formed mostly by subduction of the Indian and Australian plates under the Eurasian Plate. Thrust-faulting here caused the December earthquake — releasing centuries of pent-up energy. The Sumatra-Andaman quake registered at a magnitude greater than 9 some estimates range as high as 9.

Aftershocks continued through February across a zone that stretched more than 1, kilometers. Witnesses in the Indonesian city of Banda Aceh, with a population of more than ,, reported five to six minutes of violent shaking and a few collapsed buildings during the main quake the aftershocks caused more damage with subsequent, repeated shaking.

The Dec. The tsunami waves hit 11 countries around the Indian Ocean, stretching from Indonesia to India to Somalia. Unlike common wind- or current-driven waves, tsunamis do not travel with a rolling motion but rather with a vertical up-and-down pattern. This is because the ground motion during the earthquake displaces water , pushing the water column up and out of the way, and traveling across the ocean at speeds o' to 1, kilometers per hour, about the same as a commercial jet.

But this changes drastically as the tsunami approaches shore: Because the wave propagates through the whole water column, when it enters shallower water, it compresses, slows and rises up, packing its energy into less water. Sometimes, as was the case in the Indian Ocean in , the pull of this rising wave is so great that the water recedes from beaches.

This can be like a high tide moving in quickly but with minimal flooding, or it can be a wall of destruction that crashes inland for hundreds of meters. While dramatic, this first wall of water is not always the most dangerous. Tsunamis are usually part of a series of waves, called a tsunami wave train. In Indonesia, Thailand, Myanmar and other countries close to the epicenter, huge waves washed over coastlines. The tsunami towered at 30 meters tall and sometimes higher, but witnesses say the waters were less wave-like and more like the surge from a powerful river or a sudden flood.

The waves swallowed boats offshore, tore up docks and washed over beaches within a minute, pushing debris farther inland into populated areas. Hotels, shops, homes and streets were flooded and ripped apart as cars, trees and parts of other buildings slammed into them. The force of the water and the debris created treacherous, fast-moving currents. These currents were just as strong when the tsunami waves retreated, drawing many people out to sea. Satellite imagery shows before and after shots of coastal agriculture near Banda Aceh, Indonesia.

Credit: NASA. These waves then cross the Andaman Sea toward Thailand. Trackline red line of the Jason-1 ascending orbit 2 hours after the Sumatra-Andaman eathquake. The satellite orbits the Earth at an altitude of approximaely km. Blue arc represents the modeled wavefront direct arrival of the outbound tsunami from seafloor displacement caused by the earthquake.

Green arc represents one of many tsunami reflections. View to the north. Most instrumental measurements of tsunamis are from tide gauge stations , and more recently, bottom pressure recorders in the deep ocean. During the Indian Ocean tsunami was the first time that satellites collected transects of sea-height data using radar altimetry that clearly showed a tsunami signal during its propagation across the Indian Ocean.

It was by coincidence that the satellites passed over the Indian Ocean at the same time that the first part of the tsunami was propagating from the Sumatra-Andaman source region. Jason-1 yielded the best data to shed light on tsunami generation for this event: this satellite collected almost continuous sea-height data just two hours after the earthquake.

Five minutes later, the Topex-Poseidon satellite a tandem mission with Jason-1 collected intermittant sea-height data of the tsunami. Because the ground speed for the Jason-1 satellite is 5. In the computer model of the wavefield shown here, the blue arc represents the wavefront of the distant far-field tsunami that emanated directly from the source i. This part of the tsunami wavefield is termed the direct arrival and has almost arrived at India at this time.

The smaller amplitude waves that trail behind the blue arc are an effect of dispersion, where shorter wavelength components travel at a slightly slower speed than the wavefront. The green arc represents one of many tsunami refelctions from coastlines and submerged bathymetric features that are also detected and measured by satellite radar altimetry. Jason-1 measured the height of the tsunami wave where its trackline crossed these arcs.

To the east, the local tsunami continues to cause major wave action along the Sumatran coast. This animation above shows the evolution of tsunami waves caused by the December 26, earthquake, with the individual tsunami phases labelled.

This simulation has more vertical exaggeration than the previous view to the north, in order to better highlight the phases. Phases d1, d2, and d3 are direct tsunami wave arrivals from source regions located from south to north where fault slip occured along the Sumatra-Andaman subduction zone.

The phases beginning with the letter r originated as reflections from various coastlines and bathymetric features. The animation ends two hours after the earthquake when the Jason-1 satellite passes through the Bay of Bengal.

The Jason-1 trackline is colored pink where the model amplitudes are positive and colored blue where they are negative. The sea height along the Jason-1 transect is shown in the graph. The high amplitude double peak south of the Equator is primarily the two direct arrivals from the source region d1 and d2 , although reflections from the ninety-east ridge re , may also cross the trackline at about the same location as the d2 phase.

A stochastic slip model can be used to represent many different rupture patterns that are consistent with the frequency content observed on seismograms.

Shown in the next figure is the vertical displacement of the seafloor for the slip model that best reproduces the double-peak in the Jason-1 satellite altimetry data.

Possible source regions that give rise to tsunami phases d1 and d2 are labeled. Other possible sources such as secondary faulting can also explain the double peak. Map of computed vertical seafloor displacement that best fits the Jason-1 satellite altimetry data. Possible source regions linked to phases d1 and d2 double peak on satellite altimetry are labeled. Although there was intense strong ground shaking and heavy damage associated with this earthquake, the tsunami was much less than expected.

We can understand the factors that influence tsunami severity by comparing this event with the Sumatra-Andaman earthquake and other earthquakes along the Sunda subduction zone.

Each of these factors are described in more detail below. Animations of both the and events show how these factors combine to produce very different tsunamis. The plot shows local tsunami intensity as a function of earthquake magnitude M for a number of tsunamis that have occurred in the past century. Recent tsunamis generated by earthquakes along the Sunda subduction zone are indicated by the yellow stars. In general, tsunami size increases with earthquake magnitude, although there is significant variation in this relationship.

In contrast, the Java earthquake produced a larger than expected tsunami and is among a class of earthquakes called tsunami earthquakes. Comparison of vertical displacement profiles for the case of imbedded faulting solid line and surface faulting dashed line.

If slip during an inter-plate thrust earthquake occurs near the oceanic trench marking where the fault intersects the sea floor, three things happen to increase local tsunami severity: 1 rupture can break through to the trench, increasing slip on the fault; 2 vertical displacement will be greater because of the shallow fault depth below the sea floor; and 3 , there will be greater shoaling amplification of the tsunami see Panel 3 of Life of a Tsunami because the vertical displacement is beneath deeper water.

For the Sumatra-Andaman earthquake, the rupture started at the epicenter and spread throughout the region indicated by the finite fault model of the southern part of the rupture zone derived from global recordings of the earthquake. Analysis of the satellite altimetry data indicates that the southern rupture zone most likely extended to the Sunda Trench and broke through the sea floor as surface faulting.

Holding all other parameters of the earthquake constant, a tsunami generated by a sea-floor rupture is greater than one generated by an earthquake that does not rupture the sea floor i. The graph shows a comparison of the vertical displacement profiles for the two cases. In addition, if vertical displacement of the sea floor occurs beneath deep water, then the tsunami become greater as it travels toward shore, owing to shoaling amplification.

In the figure below, we show the difference between the initial tsunamis generated from the December top and March bottom caused by differences in earthquake magnitude as well as how close to the trench the fault ruptured. Comparison of the Sumatra-Andaman top and northern Sumatra bottom earthquakes in terms of the initial tsunami wavefield.

View to the northwest. Because most of the rupture area for tsunami earthquakes occurs near oceanic trenches for example, see the Java finite fault model , tsunami runup is consistently higher for tsunami earthquakes compared to typical inter-plate thrust earthquakes as shown in the figure above.

Tsunami beaming pattern associated with the Sumatra-Andaman earthquake. Lighter colors represent higher open-ocean tsunami amplitudes. Tsunami beaming pattern associated with the northern Sumatra earthquake. Tsunami beaming refers to the higher tsunami amplitudes in a direction perpendicular to fault orientation during open-ocean propagation. Although tsunami waves are often described as waves spreading out in all directions like when you throw a pebble into a pond , for long earthquake ruptures, tsunami amplitudes are greater along the azimuth of tsunami beaming.