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North Sumatra (Singkil) earthquake, 6-Sep-2011, Magnitude 6.6

07 Sep 2011

A magnitude 6.6 earthquake struck Singkil, in North Sumatra province, about an hour past midnight local time on Tuesday, 6-Sep-2011. BNPB, the Indonesian National Disaster Management Agency, reports over 500 buildings with heavy damage and nearly 1500 buildings with light or moderate damage. There are three reported deaths, including a young boy killed by a partial collapse of a house. The earthquake was also felt in the city of Medan, about 100km away, causing a power outage thereand prompting some residents to evacuate their homes.

This earthquake appears to have occurred within the subducting plate beneath Sumatra, at a depth of about 100km. There, the Indo-Australian plate dives beneath the Eurasian (Sunda) plate. Unlike shallower subduction zone earthquakes in which two plates slide against each other, this earthquake likely happened along a fault (break) within the descending plate. This earthquake did not produce a tsunami because it occurred in a deep part of the subduction zone, far from the ocean trench.

All along western Sumatra, the process of subduction has caused many major earthquakes and tsunamis, including the 2004 Aceh-Andaman, 2005 Nias, and 2007 Bengkulu, 2009 Padang, and 2010 South Pagai earthquakes. This area continues to face a high hazard of earthquakes and tsunamis, particularly along the Mentawai segment of the plate boundary in West Sumatra province.

Science does not allow us to predict the day, month, or year that an earthquake will occur. However, scientific research can identify which areas face higher or lower hazard. There are many ways to reduce human vulnerability to earthquakes and tsunamis, such as ensuring that houses are resistant to earthquakes, identifying tsunami evacuation routes and practicing evacuation simulations.

Further information about this earthquake: