Tectonic Summary

The October 25, 2010, M 7.8 Pulau Pagai Selatan (Mentawai), Sumatra, earthquake occurred as the result of shallow thrust faulting on or near the subduction interface plate boundary between the Australia and Sunda plates. At the location of this earthquake, the Australia plate moves north-northeast relative to the Sunda plate at a velocity of about 57–69 mm/yr. On the basis of the currently available faulting mechanism information and earthquake depth it is likely that this earthquake occurred along the plate interface.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Thrust-faulting events of the size of the October 25, 2010, earthquake are typically about 120x50 km (length x width); modeling of this earthquake implies similar dimensions, predominantly up-dip of the hypocenter.

The subduction zone adjacent to the region of this event last slipped during the M 8.5 and 7.9 earthquakes of September 2007, and the October 25th event appears to have occurred near the up-dip edge of the rupture zones of those earthquakes. The October 25th earthquake is the latest in a sequence of large ruptures along the Sunda megathrust, including a M 9.1 earthquake that ruptured to within 800 km north of this earthquake in December 2004; a M 8.6 earthquake 700 km to the north between Nias and Simeulue in March 2005; and a M 7.6 earthquake 300 km to the north near Padang in September 2009. The October 25th earthquake also occurred near the southern edge of a M 8.7–8.9 rupture in 1797 and within the rupture area of a M 8.9–9.1 earthquake in 1833.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)

Event Details

Event Map

Tectonic Summary

Tectonic Summary

Historical Magnitude 4.5+ (100km)