M 7.3 - 29 km S of Aktash, Russia

Tectonic Summary

The September 27, 2003, M 7.3 earthquake in southwestern Siberia, Russia, occurred as the result of shallow strike-slip faulting within the Altay Mountains of the Eurasia plate. Focal mechanism solutions indicate that rupture occurred on either a left-lateral southwest-striking fault or a right-lateral southeast-striking fault. Finite-fault modeling of satellite data and geological field mapping both indicate that rupture occurred on a right-lateral northwest-striking fault that was unrecognized prior to the earthquake.

This earthquake resulted from stresses originating with the collision of the India plate against the Eurasia plate. The collision of the two major plates has generated the Himalaya Mountains, far to the south of the epicenter of this earthquake, and produces deformation of the Earth’s crust over a broad region of central and eastern Asia. In the epicentral region of southern Russia, northwestern China, eastern Kazakhstan, and western Mongolia, earthquakes of past decades have been caused by strike-slip faulting (as with this earthquake) and reverse faulting.

The September 27th event is the largest in this region since an earthquake on December 20, 1761, that is thought to have had a magnitude of about 7.7.

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)