Calibration of 3D Upper Mantle Structure in Eurasia Using Regional and Teleseismic Full Waveform Seismic Data

摘要

We present progress in the development of a new approach to develop and evaluate earth models at the regional scale that utilizes full waveform seismograms. We have implemented an approach which relies on a cascade of increasingly accurate theoretical approximations for the computation of the seismic wavefield, with the goal to develop a model of regional structure for a subregion of Southeast Asia (longitude 75 to 150 degrees and latitude 0 to 45 degrees). The selected area is highly heterogeneous, presenting a challenge for calibration purposes, but is well surrounded by earthquake sources and includes high quality broadband digital stations. In previous years, we developed preliminary models based on successively more sophisticated theoretical approaches to time domain inversion of long period seismograms, in the framework of normal mode theory: (1) a 3D model based on the Nonlinear Asymptotic Coupling Theory (NACT), which includes the consideration of 2D kernels in the vertical plane containing source and receiver. This model was developed for a larger region (longitude 30-150 degrees and latitude -10 to 60 degrees); (2) a 3D model based on the 'NBorn' approximation. This approach combines the 3D Born approximation with the path average approximation (PAVA) and allows to accurately account for large accumulated phase delays on paths that sample large scale smooth anomalies. The resulting model has a horizontal resolution of about 200 km. In parallel, a regional version of the Spectral Element Method (SEM) code, in spherical geometry, RegSEM.1, was completed. This code uses Perfectly-Matched Layers (PMLs) at the borders of the region, and includes general 3D anisotropy, Moho and surface topography, ocean bathymetry, attenuation, and ellipticity. Because each SEM run (i.e., for one event) is time consuming, we proposed implementing an approach in which the wavefields for several events are computed simultaneously.