Crustal Structure of Sri Lanka Derived From Joint Inversion of Surface Wave Dispersion and Receiver Functions Using a Bayesian Approach

Abstract

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 intracrustal (18–27 km), slightly westward dipping (∼4.3°) 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 Wanni Complex/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.

Shallow Crustal Shear Velocity and Vp/Vs Across Southern California: Joint Inversion of Short‐Period Rayleigh Wave Ellipticity, Phase Velocity, and Teleseismic Receiver Functions

“…In order to provide a model with resolution of Vs and Vp/Vs in the upper few km, we combine the complementary sensitivities of Rayleigh-wave phase velocities (upper crust), ellipticity (upper few km), and the initial pulse of teleseismic receiver functions (shallow Vp/Vs ratio and shallow interfaces) to create a self-consistent model at the regional scale across southern California. The idea to combine receiver functions and surface wave data in a Bayesian joint inversion to determine Vs and Vp/Vs is relatively new (Dreiling et al, 2020;Ojo et al, 2019), and only recently shown to be promising in resolving near-surface Vs and Vp/Vs in sediments (Li et al, 2019). By including Vp/Vs as a parameter we are able to fit receiver functions on a regional scale for the first time across 231 Southern California stations, including in basins where receiver functions have long been discarded as nuisance signals or "corrected" with ad-hoc models, as reverberations overprint Moho and other crustal signatures (e.g., Yeck et al, 2013).…”

Upper-lithospheric structure of northeastern Venezuela from joint inversion of surface-wave dispersion and receiver functions

“…Lower values of V p /V s (< 1.65) are found in the Espino Graben and Peninsula of Paria. In both regions mafic rocks have been reported as (a) basaltic layers found inside the Espino Graben (e.g., Feo-Codecido et al, 1984) and (b) the dacitic rocks (porphyritic rhyolite; Alvarado, 2005) found in the Serranía del Interior. Our results appear inconsistent with the lithology of the regions, suggesting the values are most likely related to the high density of faults in both areas.…”

“…However, our results for the area with the thickest crust are counter-intuitive with regard to standard foreland basin configurations, where the depocenter of the basin is associated with the deepest flexure and the deepest Moho (e.g., Watts, 2001). In the eastern Venezuela Basin, the deepest sediments (∼ 10 km;Feo-Codecido et al, 1984;Di Croce, 1995;Clark et al, 2008;Bezada et al, 2010) are found in the Espino Graben and Maturín sub-basin, located north and northeast of the region with greatest Moho depths. We find the trend and location of the thickest crust are relatively consistent with the location of the contact between the Precambrian basement (i.e., the Guiana Shield extending beneath the sedimentary layers north of the Orinoco River) and the Cambrian basement found between the Espino Graben and the shield (e.g., Feo-Codecido et al, 1984;Di Croce, 1995).…”

“…In the eastern Venezuela Basin, the deepest sediments (∼ 10 km;Feo-Codecido et al, 1984;Di Croce, 1995;Clark et al, 2008;Bezada et al, 2010) are found in the Espino Graben and Maturín sub-basin, located north and northeast of the region with greatest Moho depths. We find the trend and location of the thickest crust are relatively consistent with the location of the contact between the Precambrian basement (i.e., the Guiana Shield extending beneath the sedimentary layers north of the Orinoco River) and the Cambrian basement found between the Espino Graben and the shield (e.g., Feo-Codecido et al, 1984;Di Croce, 1995). We suggest that this indicates that the allochthonous Paleozoic terrains accreted to the north of the Guiana Shield either had a crustal thickness larger than the shield itself or, alternatively, that the accretion process deformed the crust in such a way that now the deepest Moho is found on this contact.…”

Crustal structure of Sri Lanka derived from joint inversion of surface wave dispersion and receiver functions using a Bayesian approach

“…The Mannar Basin (west of Sri Lanka, partly onshore, Figure 1) has been formed during Gondwana breakup, which initiated at approximately 165 Ma (Royer & Coffin, 1992). A great amount of rifting between India and Sri Lanka together with strike slip movement and anticlockwise rotation of Sri Lanka was responsible for significant widening and rapid subsidence in the basin (Kularathna et al, 2015) and is associated with strong crustal thinning along the west coast.…”