Why Earthquake 8.5 on the Richter Scale caused a small tsunami in Aceh?

Wednesday (4/11/2012), at 15:38 pm, an earthquake with a strength of 8.5 on the Richter scale rocked Aceh. The epicenter is located at 346 kilometers southwest of Simeulue. The quake was followed by at least 16 aftershocks. Furthermore, at 17:43 pm, another earthquake with a strength of 8.1 on the Richter scale, centered at 483 kilometers from the city of Simeulue. The quake was followed by 11 aftershocks. Major earthquake could certainly cause a big tsunami, but only a small tsunami of about 10-80 cm. Why so?

Tsunami in Aceh yesterday only a small scale because of the location of the epicenter is located outside the subduction zone. Subduction zones are zones where two plates meeting. Known, the first earthquake and numerous aftershocks that occurred centered in the subduction zone west, away from the mainland island of Sumatra. The quake was different with the earthquake in Aceh in 2004. If the epicenter was outside of subduction zones, tsunami potential stay there, but smaller. The quake also occurred due to shear faults, rather than up or down.

There are three fault movement, namely vertical, horizontal, and oblique (oblique). Vertical fault motion over the potential to cause tsunami. At this time the earthquake, fault movement that occurs is tilted, flat-dominated fault movement. Thus, the tsunami could happen, but very small.

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