LDEO Seismogram and Focal Mechanisms for the 12/26/04 Sumatra Earthquake & Aftershocks

The focal mechanism of the mainshock indicates low angle thrust faulting (dipping 8 degree NE) along a plane striking NNW (329 deg) at a depth of about 29 km. The largest aftershock (Mw 7.1) that occurred northwest of the mainshock in Nicobar Islands appears to be more northerly striking (352 deg), shallow (12 km) and steeply dipping (41 deg). The second largest aftershock also has similar focal mechanism to the largest aftershock. Eight (8) major earthquakes (Mw > 7) during 1976-2004 in the region indicates that low angle, thrust faulting is the predominant mechanisms in the region. Calculated by Won-Young Kim of Lamont-Doherty Earth Observatory.