3D local earthquake tomography of the Andaman-Nicobar subduction zone using ocean-bottom seismometer data

Abstract

The Andaman-Nicobar (A-N) subduction zone is one of the most seismically active subduction zones of the world where the Indian plate subducts beneath the Burmese-Sunda plate. Imaging the subducting Indian plate (SIP) geometry in this region is important to understand the subduction process, earthquake genesis, and associated seismic hazards. Therefore, we imaged the SIP for the first time using local earthquake data recorded from a network of nine ocean-bottom seismometers and six surface seismic stations. We inverted 2819 P and 2171 S phases picked from 410 local earthquakes recorded between December 2013 and May 2014 to obtain the tomographic images in the A-N region. The images show high-VP and VP/VS anomalies linked to colder and thicker SIP in the A-N region. We also observed seismic signatures of strong structural heterogeneity all along the SIP. The low-velocity anomaly at 60-100�km depth beneath the Andaman back-arc spreading center indicates mantle upwelling. Likewise, low-VP anomalies beneath the active volcano Barren Island indicate production of arc magmas by slab dehydration and corner flow in the mantle wedge.