Jennifer Dreiling, Frederik Tilmann, Xiaohui Yuan, Christian Haberland, S.W. Mahinda Seneviratne

We study the crustal structure of Sri Lanka by analyzing data from a temporary seismic network deployed in 2016--2017 to shed light on the amalgamation process from a geophysical perspective. Rayleigh wave phase dispersion curves from ambient noise cross-correlation and receiver functions were jointly inverted using a transdimensional Bayesian approach.

The Moho depths in Sri Lanka range between 30 and 40~km, with the thickest crust (38-40 km) beneath the central Highland Complex (HC). The thinnest crust (30-35 km) is found along the west coast, which experienced crustal thinning associated with the formation of the Mannar Basin. Vp/Vs ratios lie within a range of 1.60-1.82 and predominantly favor a felsic to intermediate bulk crustal composition with a significant silica content of the rocks.

A major intra-crustal (18-27~km), slightly westward dipping (~4.3$^\circ$) interface with high Vs (~4 km/s) underneath is prominent in the central HC, continuing into the western Vijayan Complex (VC). The discontinuity might have been part of the respective units prior to the collision and could be an indicator for the proposed tilting of the WC/HC crustal sections. It might also be related to the deep crustal HC/VC thrust contact with the VC as an indenting promontory of high Vs. A low velocity zone in the central HC could have been caused by fluid influx generated by the thrusting process.