High-resolution ambient noise adjoint tomography of the crust and upper mantle beneath the eastern margin of the Tibetan plateau
Tuesday, 16 December 2014
Mechanism on the uplift and deformation of the eastern margin of the Tibetan plateau is still debated, partly due to lack of a high-resolution 3-D seismic image of the crust and upper mantle beneath this region. We took advantage of the unprecedented station coverage and utilized empirical Green’s functions of Rayleigh waves extracted from 2-year ambient noise data of the vertical recordings. We started from a 3-D Vsv model produced by traditional ambient noise tomography [Yang et al., 2012] and implemented the traveltime adjoint tomography to iteratively update the initial model and finally approached a 3-D Vsv model with higher velocity contrast. In this process, with the aid of the highly accurate spectral element method (SEM), we employed 3D frequency dependent kernels that fully account lateral heterogeneities when investigating the Rayleigh wave dispersive property. Our preliminary result reveals a prominent low Vsv layer at depths ~20-40 km beneath the plateau. We interpreted it as inflated middle crust, which may have been squeezed to the margin from the center of the plateau. The mantle Vsv at ~80 km beneath the plateau appears to be significantly low, which might imply a thin lithosphere beneath the margin.