Tomographic Pn and Sn velocity beneath the continental collision zone from Alps to Himalaya

Abstract

[1] We have obtained Vp and Vs velocity images of the uppermost mantle beneath the continental collision zone from the Alps to the Himalaya by performing tomographic inversion using both Pn and Sn travel times. 654,999 Pn arrivals and 121,838 Sn arrivals were selected from the joint database including ISC/EHB, Iran bulletin and the Annual Bulletin of Chinese Earthquakes. Average Pn and Sn velocities are 8.04 km/s and 4.60 km/s, respectively, and maximum velocity perturbations are about 6%. Pn velocity correlates well with topography. In general, mountains, with high elevations, show low velocity, while the seas, basins and plains with low elevations show high velocity because the mountains are collision zones with strong tectonic activity and the low elevation areas are stable plates. The large tectonic lines are boundaries between high and low Pn velocity, such as plate boundaries, sutures and faults between plates and orogens. Sn velocity shows a very similar pattern to Pn velocity. A geodynamic cartoon is proposed to show the relationship between velocity and tectonics, indicating that the sutures are boundaries with high dip angles and the plate boundaries are low angle reverse faults in the region.