Group velocity tomography of the Indo-Eurasian collision zone

Abstract

We present results of a Rayleigh and Love wave group velocity dispersion study of the Indo-Eurasian collision zone. Group velocity dispersion curves are measured and combined to produce dispersion maps for 10–70 s period Rayleigh waves from 4054 paths and for 15–70 s Love waves from 1946 paths. Group velocity maps benefit from the inclusion of data recorded at a large number of stations within India, an advantage over previous global studies. This has the largest impact at short periods as a result of the improved path length distribution. Synthetic tests are used to estimate resolution, which ranges from 3° to 5° on the continents for Rayleigh wave maps and from 5° to 7.5° for Love wave maps. Group velocities correspond well with known geological and tectonic features and show good correlation with sediment thickness at short periods. The cratons of the Indian Shield can be distinguished in the short-period and midperiod group velocities. Group velocities are slow across Tibet until 70 s whereas the cratonic cores of the Indian Shield appear as a high velocity anomaly at 70 s. Dispersion curves extracted from the Rayleigh wave group velocity maps are inverted for shear wave velocity as a function of depth for profiles across India and Tibet. The relationship between shear velocity contours and the Moho indicated by receiver function studies has been used to obtain a first-order estimate of crustal thickness across the collision zone. Results suggest a slow Tibetan midcrust and low sub-Moho velocities beneath the central and northeastern Tibetan Plateau.