Home – Home – Jornals – Russian Geology and Geophysics 2006 number 11

The preseismic stress field on the western flank of the Sunda seismic arc before the great Sumatra-Andaman earthquake modeled from earthquake mechanism data shows a heterogeneous pattern in the area of the pending source. The first motion in the source of the coming great event occurred within the region of high deviatoric and isotropic stresses near their steepest gradients. Seismic radiation in the earthquake culminated in the zone of lowest stress extending for about 350 km along the northern edge of Sumatra Island as far as the Nicobar Islands. The revealed stress distribution in the earthquake nucleation area agrees well with laboratory experiments on rock failure in which low and medium stresses correspond to brittle failure. The suggested model of the metastable state of rocks in seismogenic regions includes the presence of different stress zones and the formation of a zone of high stress gradient in the place of the pending bigger earthquake.