28.10.2010 | Potsdam: On 25/10/2010 at 14:42:21 UTC (= 21:42:21 local time), a strong submarine earthquake with a magnitude of 7.8 occurred about 25 km southwest of the Pagai island in the Sunda Arc off Sumatra (Indonesia). This triggered a tsunami, which devastated in particular the Mentawai Islands, to which which Pagai belongs. The exact number of earthquake and tsunami victims is currently unknown, first estimates are on more than 300 dead.

Already at 14:47:06 UTC (21:47:06 local time, 04 min 46 sec later) the warning system of the Tsunami Warning Centre in Jakarta triggered the tsunami alert. Due to its proximity to the epicenter of the earthquake, the tsunami already arrived around the same time on the island of Pagai, which is probably most affected, many houses here were destroyed by the earthquake and subsequent tsunami.

The tsunami warning was sent from the warning center via satellite to some 400 institutions such as police and local emergency services. The media (TV, radio, internet) also distributed the warning. The main island of the Mentawais received this alert as well.

Contrary to reports stating otherwise, all components of the tsunami early warning system worked properly. Reports of broken or even deliberately destroyed system units are entirely unfounded. The detection of the causative earthquake by the seismic network was almost in real time, the corresponding operational image showed relevant warning levels in particular for the western coastline of the Mentawai Islands. The measurement of the tsunami at gauging stations on the islands and along the coast of Sumatra was accurate, the station at Padang registered the incoming tsunami after 55 minutes correctly with 31 cm wave height. The difference in wave height between the Island of Pagai and the coast of Sumatra is due to the earthquake process itself: most of the energy was radiated in a southwestly direction, to the open sea. The Mentawai Islands also acted as a breakwater in the direction of main island of Sumatra. Therefore, the tsunami alert could lifted after only 56 minutes.

As with the tsunami of Samoa on 30/09/2009 in the Pacific it is shown here that a comprehensive protection against earthquakes and tsunamis is not possible: directly at the source the earthquake and the arrival of the tsunami occur almost simultaneously. The greater the distance to the location of the earthquake, the longer the prewarning time. The risk is very high for the inhabitants of the island chain off Indonesia. The presence of an effective tsunami early warning system should not be reinterpreted in a complete protection from a catastrophe. Counteracting this false sense of security is part of the work of the tsunami early warning system for Indonesia.

Images in printable resolution

Information on the earthquake

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