Seismic structure across central Myanmar from joint inversion of receiver functions and Rayleigh wave dispersion

The active tectonics in Myanmar is governed by the ongoing northward indentation and obliquely-eastward subduction of India into Eurasia. So far, detailed seismic structure of the crust and uppermost mantle at the eastern flank of the India-Eurasia collision zone remains highly debated. With seismic waveforms recorded at 79 broadband stations in Myanmar, we build a regional shear velocity model in the depth range of 0-80 km by joint inversion of ambient noise derived Rayleigh wave dispersion and P-wave receiver functions. Common conversion point stacking was performed along two representative profiles. We observe clear variations in the seismic velocity and discontinuity structures beneath this region. 1) A sedimentary layer covers the eastern fore-arc trough of the Central Myanmar Basin, with shear velocity less than 2.5 km/s and thickness increasing from similar to 8 km at 22 degrees N to similar to 18 km at 23 degrees N. The fore-arc Chindwin basin is evidently thicker than the back-arc Shwebo basin, an abrupt drop in sediment thickness towards the east appears immediately below the Wuntho-Popa magmatic arc. 2) Crustal low-velocity (LV) anomalies (<3.3 km/s) in the Indo-Burma Ranges probably reflect the Bengal sediments accreted to the toe of the overlying Burma plate, 3) The underlying LV layer with a thickness of over 20 km below the Burma Moho (30-40 km in depth) is indicative of the eastward subduction of the Indian continental crust, the top boundary of which is imaged with a dip angle of similar to 20 degrees. 4) Upper mantle LV anomalies filling the majority of the back-arc domain at depths greater than 60 km display a connection to a small-scale, subcrustal LV body beneath the Monywa volcano, possibly forming a fluid- or melt-rich mantle channel.