Indonesia Tsunami Map

(www.geology.com)
A great earthquake occurred at 00:58:53 (UTC) on Sunday, December 26, 2004. This 9.0+ magntide event was located off the west coast of Northern Sumatra as shown on the map below. This was the fourth largest earthquake in the world since 1900 and the largest since the 1964 Prince William Sound, Alaska earthquake. The tsunami caused more casualties than any other in recorded history. Over 150,000 people were killed, over 25,000 were missing and over 1,000,000 were displaced in South Asia and East Africa. At least 110,229 people were killed in Indonesia, 30,922 people in Sri Lanka, 10,749 in India, 5,303 in Thailand, 150 in Somalia, 81 in Maldives, 68 in Malaysia, 59 in Myanmar, 10 in Tanzania, 3 in Seychelles, 2 in Bangladesh and 1 in Kenya.

Tsunami Earthquake Map

The map below shows the location of this earthquake and some of the many aftershocks. It occurred at a convergent boundary where the Indian plate subducts beneath the Burma Plate.

Tsunami Epicenter Map

Prior to this earthquake the Indian Plate was moving beneath the Burma Plate, meeting resistance and compressional forces accumulated. When the fault between these two plates suddenly slipped a rupture approximately 1,200 kilometers long developed in the ocean floor with a vertical displacement of about 15 meters. The boundary between the plates and the line of failure are shown on the map below as the blue saw-tooth line.

Tsunami Travel Time Map

The tsunami produced by the earthquake traveled across the Indian Ocean causing significant damage. A modeled travel time map for this event is shown below. Note how the wave traveled across the Indian Ocean, striking India within about two hours and Aftica about 6 hours later.

Tsunamis Wave Height Map

The modeled tsunami wave height map below shows the maximum heights that the wave likely reached when it came ashore. The coastline of Sumatra, near the earthquake event, received waves over 10 meters tall. Areas farther away such as Sri Lanka and Thailand were struck by waves over 4 meters tall. On the other side of the Indian Ocean, Somalia and the Seychelles here struck by waves approximately 4 meters in height.

.

»»  read more

Tsunami Geology - What Causes a Tsunami?

What causes a tsunami?... A tsunami is a large ocean wave that is caused by sudden motion on the ocean floor. This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami. Tsunamis travel across the open ocean at great speeds and build into large deadly waves in the shallow water of a shoreline.

Subduction Zones are Potential Tsunami Locations

Most tsunamis are caused by earthquakes generated in a subduction zone, an area where an oceanic plate is being forced down into the mantle by plate tectonic forces. The friction between the subducting plate and the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the two plates become "stuck".

Accumulated Seismic Energy

As the stuck plate continues to descend into the mantle the motion causes a slow distortion of the overriding plage. The result is an accumulation of energy very similar to the energy stored in a compressed spring. Energy can accumulate in the overriding plate over a long period of time - decades or even centuries.

Earthquake Causes Tsunami

Energy accumulates in the overriding plate until it exceeds the frictional forces between the two stuck plates. When this happens, the overriding plate snaps back into an unrestrained position. This sudden motion is the cause of the tsunami - because it gives an enormous shove to the overlying water. At the same time, inland areas of the overriding plate are suddenly lowered

Tsunami Races Away From the Epicenter

The moving wave begins travelling out from where the earthquake has occurred. Some of the water travels out and across the ocean basin, and, at the same time, water rushes landward to flood the recently lowered shoreline.

Tsunamis Travel Rapidly Across Ocean Basis

Tsunamis travel swiftly across the open ocean. The map below shows how a tsunami produced by an earthquake along the coast of Chile in 1960 traveled across the Pacific Ocean, reaching Hawaii in about 15 hours and Japan in less than 24 hours.

Tsunami "Wave Train"

Many people have the mistaken belief that tsunamis are single waves. They are not. Instead tsunamis are "wave trains" consisting of multiple waves. The chart below is a tidal gauge record from Onagawa, Japan beginning at the time of the 1960 Chile earthquake. Time is plotted along the horizontal axis and water level is plotted on the vertical axis. Note the normal rise and fall of the ocean surface, caused by tides, during the early part of this record. Then recorded are a few waves a little larger than normal followed by several much larger waves. In many tsunami events the shoreline is pounded by repeated large waves.
(www.geology.com)

»»  read more