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Myanmar
Subduction zone
Joint inversion
S-wave velocity structure
Seismic discontinuity
Abstract:
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 ~8 km at 22°N to ~18 km at 23°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 ~20°. 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.
