Application of Gaussian-Beam Migration to Multiscale Imaging of the Lithosphere beneath the Hi-CLIMB Array in Tibet

Abstract

Abstract In this study, we apply Gaussian-beam (GB) migration of scattered teleseismic P waves to image the crust and upper mantle beneath Tibet using data from the Hi-CLIMB experiment. We use teleseismic P waves from three groups of earthquakes to the southeast, northeast, and northwest of the Hi-CLIMB array, each within a narrow range of azimuth and distance, to obtain stacked radial receiver functions, which we then use to image the lithosphere by GB migration. We produced images at several different frequency bands in order to constrain the multiscale scattering properties of the lithosphere. For each frequency band, three GB images are generated, each from earthquake sources in a distinct back-azimuth group. The three images are then stacked to form a composite image. The imaged Moho is generally strong and continuous under much of the Lhasa terrane in southern Tibet, corresponding to a well-defined Moho. A major disrupted zone in Moho scattering, extending over 200 km in length, is evident in the vicinity of the Bangong–Nujiang suture, where there is also increased crustal scattering. The disrupted zone marks the diffuse, subsurface join between stable portions of mantle lithosphere under southern and central Tibet, respectively. At the northern end of the profile in the Qiangtang terrane there is an increase in Moho reflectivity but at a shallower depth than under the Lhasa terrane. Comparable length scales of about 200 km between regions with disrupted and smooth-varying Moho suggest that the mechanically strong mantle lithosphere and the crust respond differently to collision, with the upper crust currently undergoing pervasive strain over the entire plateau.