Abstract
The Burmese-Andaman Arc System (BAAS) and the West Sunda Arc (WSA) in NE Indian Ocean are well known for their high seismic hazard and tsunami potentiality. Seismicity is caused by eastward subduction of the Indian plate to intermediate focal depths below the BAAS, but the penetration depth goes even deeper to about 500 km below the WSA. The seismicity map and its correlation to crustal and mantle faults for this extensive plate margin are presented. This is achieved by using frequency-magnitude relationship to select larger (m(b) >= 5.0) and comparatively well-recorded events from the available earthquake catalogue that span for a period of little more than a century (1906-2008). Barely 14% of the events qualify the treatment, and the events so selected are subjected to cluster analysis using a statistical function 'point density'. The clusters found for the arc demonstrate significant relationship to subduction geometry in their respective areas; 11 out of a total of 13 clusters commonly originate below the fore arc. Earthquakes within the individual clusters have linear fractal geometry consistent with the traces of seismogenic surfaces that actually produce them. Correlation of clusters to seismologic depth sections and the composite results derived from 518 CMT solutions of earthquakes establish a close spatial relationship between the shape and orientation of the clusters with stress axes and regional tectonics. This provides a three-dimensional perspective on the stress distribution within the respective clustered seismic zones. Seismic potentiality for five most conspicuous clusters is also inferred.