Seismic evidence for tearing in the subducting Indian slab beneath the Andaman arc

Abstract

Segmentation of a subduction zone through tearing is envisaged as an inevitable consequence of the differential rate of slab rollback along the strike of convergent plate boundaries. It is a key feature that controls plate tectonics and seismogenesis in a subduction setting. Globally, lithospheric tears are mostly recognized by seismic tomography and seismicity trends. However, such an intriguing feature has never been imaged with high resolution. Here we present seismological evidence for tearing of the Indian oceanic plate at shallow depths along the Andaman arc. Our image of the subducted plate using the shear-wave receiver function technique reveals three distinct plate segments. The middle lithospheric chunk has an abrupt offset of ~20 km relative to the northern and southern segments along the entire stretch of Andaman-Nicobar Islands. We interpret that this abrupt offset in the base of the lithosphere is caused by the tearing of the subducted oceanic plate. For the plate age of ~80 to 60 Myr, the lithospheric thickness varies from ~40 to 70 km.