Upper-mantle Structure beneath Myanmar by Teleseismic Body-wave Finite-frequency Tomography

Myanmar (Burma), as a part of the Eastern Himalayas Syntaxis, is a crucial region for understanding the collision between India and Asia and the subduction of the Indian plate. In this study, we present new tomography models of P- and S-wave velocity structures in the upper mantle beneath Myanmar region. The tomographic images were constructed using the teleseismic data from 71 temporary stations of the newly deployed China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO) seismic network, as well as other 615 seismic stations in Myanmar and its adjacent areas. Our tomographic models show prominent features of three parallel east-dipping velocity bodies, including two high-velocity structures beneath the Indo-Burma Ranges and the Sagaing fault, and a low-velocity body sandwiched between them. The high-velocity body beneath the Indo-Burma Ranges has a thickness of approximate 100 km and maximum velocity perturbations of 4% and 6% for P- and S-wave, respectively. This anomaly is preferentially interpreted as the subducted Indian oceanic slab due to previous seismicity studies and its morphology and velocity structural features. The high-speed anomaly beneath the Sagaing Fault reaches only a depth of ~300km and cannot be traced further north around ~23.4°N. This is probably a remnant of the Meso-Tethyan oceanic slab based on the distribution of Triassic-early Cretaceous I-type granites through the western edge of the Sibumasu block and isotopic data of erupted lava in Tengchong. The low-velocity structure sandwiched by the two high velocity bodies extends to the depth of ~500km and ~400km in S- and P-wave inversion results respectively, and might be a signature of released water from the Mantle Transition Zone or subducted slab.

This study was financially supported by the National Natural Science Foundation of China (grant 41490612).