Rapid along-strike variations of shallow crustal structure in response to Indo-Burma subduction: constraints from multi-type passive seismic data

Characteristics of the subducting crust and the attached sedimentary cover play a key role in shaping the structure and processes in the hanging wall of a convergent plate boundary. Such influence must be significant in the oblique Indo-Burma subduction zone. Yet, the poorly resolved shallow crustal velocity structure of the overriding Burma plate, especially its lateral variation along the subduction margin, hinders a comprehensive understanding of the Indo-Burma subduction dynamics. Here, we take advantage of the new and dense broadband seismic data in Myanmar to image the regional S-wave velocity (Vs) structure in the top 10 km of crust by joint inversion of Rayleigh-wave ellipticity, receiver function and P-wave polarization. The new velocity model not only matches surface geology and seismic reflection profiles, but also reveals new and rapidly varying near-surface features, including (1) the exhumed high-velocity metamorphic belt of the Indo-Burma accretionary prism, which is more prominent in the south with a shallower depth extent and greater Vs of ∼3.5 km/s; and (2) contrasting Vs structure beneath the two Quaternary volcanoes, that is, Vs of typical crystallized igneous rocks (∼3 km/s) beneath Monywa versus Vs slower than the adjacent basin sediments (