GJI Seismology Joint inversion of surface waves and teleseismic body waves across the Tibetan collision zone: the fate of subducted Indian lithosphere

We carry out a joint inversion of surface wave dispersion curves and teleseismic shear wave arrival times across the Tibetan collision zone, from just south of the Himalaya to the Qaidam Basin at the northeastern margin of the plateau, and from the surface to 600 km depth. The surface wave data consist of Rayleigh-wave group dispersion curves, mainly in the period range from 10 to 70 s, with a maximum of 2877 source–receiver pairs. The body wave data consist of more than 8000 S-wave arrival times recorded from 356 telesesmic events. The tomographic images show a ‘wedge ’ of fast seismic velocities beneath central Tibet that starts underneath the Himalaya and reaches as far as the Bangong–Nujiang Suture (BNS). In our preferred interpretation, in central Tibet the Indian lithosphere underthrusts the plateau to approximately the BNS, and then subducts steeply. Further east, Indian lithosphere appears to be subducting at an angle of ∼45◦. We see fast seismic velocities under much of the plateau, as far as the BNS in central Tibet, and as far as the Xiangshuihe–Xiaojiang Fault in the east. At 150 km depth, the fast region is broken by an area ∼300 km wide that stretches from the northern edge of central Tibet southeastwards as far as the Himalaya. We suggest that this gap, which has been observed previously by other investigators, represents the northernmos