Joint inversion of surface wave velocity and gravity observations and its application to central Asian basins shear velocity structure

摘要

We implement and apply a method to the jointly inverted of surface wave groupvelocities and gravity anomalies observations. Surface wave dispersion measurements are sensitive to seismic shear wave velocities, and the gravity measurements supply constraints on rock density variations. Our goal is to obtain a self-consistent three-dimensional shear velocity-density model with increased resolution of shallow geologic structures. We apply the method to investigate the structure of the crust and upper mantle beneath two large central Asian sedimentary basins: the Tarim and Junggar. The basins have thick sediment sections that produce substantial regional gravity variations (up to several hundred milligals). We used gravity observations extracted from the global gravity model derived from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. We combine the gravity anomalies with high-resolution surface wave slowness tomographic maps that provide group velocity dispersion values in the period range between 8 and 100 s for a grid of locations across central Asia. To integrate these data, we use a relationship between seismic velocity and density constructed through the combination of two empirical relations. One determined by Nafe and Drake, most appropriate for sedimentary rocks, and a linear Birch's law, more applicable to denser rocks (the basement). An iterative, damped least squares inversion including smoothing is used to jointly model both data sets, using shear velocity variations as the primary model parameters. Results show high upper mantle shear velocities beneath the Tarim basin and suggest differences in lower crust and upper mantle shear velocities between the eastern and western Tarim.