Incorporating Amplitude Constraints in High Resolution Surface Wave Tomography of California

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This project will develop high resolution, 3-D anisotropic models of the elastic structure of the crust and upper mantle beneath California using both phase and amplitude information of surface waves to maximize resolution. The variation in amplitude of waves due to focusing and defocusing caused by velocity variations carries nearly as much information about the seismic velocity structure as the phase perturbations, but amplitudes have generally been neglected due to the difficulty of interpreting them. By paying careful attention to other factors that affect amplitudes, including scattering or multipathing due to heterogeneities outside the array, attenuation, site response, and instrument response, the focusing effects can be employed to refine the velocity model. In addition, the intrinsic site amplification carries information about the velocity structure beneath and in the vicinity of the station that can be incorporated directly in the tomographic inversion. Pseudospectral numerical models will be employed to test the sensitivity kernels employed in the inversion. Data from new EarthScope stations will be used to construct models of all of California and parts of adjacent Nevada. The high density of stations will yield resolution of lateral variations on scales down to tens of kilometers and constraints on vertical structure down to depths of about 200 km. Tectonic goals of interest include outlining the shape of the area beneath the Walker Lane region and southern Sierra Nevada that may have experienced lithosphere delamination and determining the thickness of anisotropic layers in the vicinity of the San Andreas fault.Broader Impact: Graduate and undergraduate students will be trained through direct involvement in the proposed research, including the probable participation of several women students over the course of the project. Results will be shared as quickly as possible with other scientists using EarthScope data, with the intent of building collaborations for joint interpretation of surface waves with other observations, including body wave tomography, shear wave splitting, and receiver function analysis. In addition, working through EarthScope, images and other information will be disseminated as soon as they become available.