Compositional Variation in the Crust of Peninsular Ranges and Surrounding Regions, Southern California, Revealed by Full-Wave Seismic and Gravity Joint Inversion

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Detailed three-dimensional models of crustal compositional variations are essential for better understanding crustal evolution and dynamics. High-resolution wave speed and density models of the crust provide one of the most important constraints on crustal compositional variations, particularly at depths beyond direct rock sampling. Here we present a three-dimensional density and wave speed model of Southern California obtained by jointly inverting gravity anomalies and seismic component-differential phase delays with full-wave sensitivity kernels, which provide a link between wave speed and density. Thus, unlike previous joint seismic and gravity inversions, the new model does not depend on an empirical relationship between wave speed and density. The resulting density and compressional-to-shear wave-speed ratio (Vp/Vs) reveal detailed features of compositional variations in the upper and middle crust in the study area, such as the three-dimensional geometry of the boundary between the western and eastern portions of the Peninsular Ranges batholith, the gabbro- and metavolcanics-rich locations within the Western Peninsular Ranges batholith, the variation of sedimentary basin thickness beneath the Coachella Valley, and a likely intermediate-to-mafic batholith beneath the Coachella Valley and the Eastern Peninsular Ranges. The jointly inverted density and Vp/Vs values also suggest a lithological control on seismic activities off the major fault zones.

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Journal of Geophysical Research: Solid Earth