Mantle Transition Zones (MTZ) discontinuities beneath the Andaman Subduction Zone

摘要

We study the mantle transition zone discontinuities beneath the Andaman Subduction Zone using receiver functions generated from broadband seismic stations. The receiver functions were geographically binned using the Common Conversion Point (CCP) technique. Moveout corrected receiver functions shows that P-SV phase conversions from 410 km discontinuity arrives around similar to 5 to similar to 7 s earlier than expected (similar to 44 s). Migrating and projecting these receiver functions along a depth profile shows that the mean apparent depth of 410 and 660 km discontinuities is 357 +/- 5 km and 660 +/- 7 km, respectively. This translates to around similar to 53 +/- 6 km elevation in 410 km discontinuity. We attribute this elevation to the perturbation in isotherm caused by the young and steep subducting slab, which results in phase transformation of Olivine (alpha- phase) to wadsleyite (beta-phase) at much earlier depth. There is no substantial topographical variation in depth of discontinuity at 660 km. We infer this flat topography of the 660 km discontinuity due to the termination of the descending slab, as evidenced in recent tomographic studies. The apparent mean MTZ thickness beneath the Andaman Subduction Zone (ASZ) is 296 +/- 6 km.