M 7.5 - Nicobar Islands, India region

Tectonic Summary

The June 12, 2010, M 7.5 Nicobar Islands earthquake occurred as a result of shallow, oblique reverse faulting near the oceanic trench defining the bathymetric expression of the plate boundary between the Indo-Australia and Sunda plates. Focal mechanism solutions indicate that rupture occurred on either a southwest- or east-southeast-striking, moderately dipping reverse fault. Of these two possible fault orientations, finite-fault modeling of globally recorded seismic data is more consistent with slip on the east-southeast-striking fault. At the location of this earthquake, the Australia and India plates move northward relative to the Sunda plate at a velocity of about 45–50 mm/yr. On the basis of the currently available faulting mechanism information, earthquake location and depth, this earthquake likely occurred within the subducting Indo-Australia oceanic plate, rather than on the interplate thrust boundary.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Reverse-faulting events of the size of the June 12, 2010, earthquake are typically about 85x30 km (length x width); modeling of this earthquake implies dimensions of about 60x40 km, predominantly surrounding the hypocenter and to the southeast.

The June 12th earthquake was located adjacent to the 1300-km-long rupture area of the devastating M 9.1 earthquake of December 2004, approximately 650 km to the northwest of the hypocenter of that event, in a region of the Australia-India plate that has experienced a broad variety of faulting mechanisms in the past.

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)