Neo-tectonics and time-space seismicity of the Andaman-Nicobar region

Abstract

The seismicity of the Andaman-Nicobar region has been analyzed in space and time. The space distribution of epicenters brings out a gap in seismicity which is situated at the northern end of Andaman Island. Such seismically quiet zones at tectonically active plate boundaries can constitute a seismic hazard in the near future. However, for this gap it could not be established that such is the case. The earthquake focal mechanism studies show that the area on the northeastern side of the arc is undergoing normal faulting along two zones enclosing a graben feature between them, which is also the area where the lrrawaddi River dumps its sedimentary load. The eastern margin of this interpreted graben is associated with a submarine channel which appears to have a seismotectonic control. The great 1941 earthquake in this area is inferred to have a nearly northsouth fault extending for about 800 km. The northern and southern edges of this fault displayed continued aftershock activity for several years. There was a general decrease in seismic activity in the entire area for three years following the great earthquake.