Return to Sumatra-Andaman Islands Earthquake Page
Epicenters of the December 26, 2004, northern Sumatra earthquake and its large aftershocks are plotted as stars. The Harvard CMT (Centroid Moment Tensor) solutions are plotted as beach-balls, which indicate mode of earthquake faulting. The mainshock was a predominantly thrust faulting (=reverse-faulting) along the fault plane gently dipping (10 degree) to the northeast. Epicenters of the 45 large aftershocks during Dec. 26-29 and determined by NEIC (National Earthquake Information Center/US Geological Survey, Golden, Colorado) are plotted with circles.
Additional six large earthquakes (Mw > 7) that occurred along the Sumatran subduction zone during 1976-2003 are plotted. Most of the mechanisms indicate thrust faulting due to convergent plate motion between the Indo-Australian and South-east Asian plates, but there are some events that show substantial strike-slip faulting mechanisms reflecting right lateral component of plate motion due to highly oblique relative motion between the Indo-Australian and South-east Asian plates. Sumatran plate boundary trends NW, whereas relative plate motion vector has N10E orientation (abut 50-60 mm/year; see Natawidjaja et al., 2004, JGR B04306).
Credit: Won-Young Kim, Lamont-Doherty Earth Observatory