Seismic Anisotropy and Mantle Deformation Beneath the Central Sunda Plate

Abstract

Abstract The central Sunda plate, which forms the core of Southeast Asia, has been extensively studied based on analyses of data mainly from surface geological observations. In contrast, largely due to the limited coverage by seismic stations in the area, a number of key issues associated with mantle structure and dynamics remain enigmatic. These can possibly be constrained by investigating seismic azimuthal anisotropy in the upper mantle. Here we employ the shear wave splitting technique on three P‐to‐S converted phases from the core‐mantle boundary (PKS, SKKS, and SKS) recorded by 11 stations to systematically explore the spatial variation of azimuthal anisotropy beneath the central Sunda plate. Most of the Malay Peninsula is revealed to possess mostly trench‐perpendicular fast orientations that can be attributed to mantle flow induced by the Indo‐Australian subduction. In addition, the central part of the Malay Peninsula is characterized by a 2‐layered model of anisotropy, which is possibly associated with the joint effects of lithospheric fabrics and a slab tear‐induced toroidal flow. Absolute plate motion (APM)‐parallel anisotropy is observed in northern Borneo and the Nansha Block, where APM‐driven simple shear in the transitional layer between the partially coupled lithosphere and asthenosphere is mostly responsible for the observed anisotropy. The APM‐induced flow may be locally modified by a fossil slab segment beneath Sabah.