Sedimentary and Crustal Structure of the Western United States From Joint Inversion of Multiple Passive Seismic Datasets

Accurate seismic images of the crust are essential for assessing seismic hazards and elucidating tectonic processes that shape surface landforms. Although California and Nevada have been studied extensively using various seismic datasets and tomographic methods, the region lacks a seismic model that can accurately define both the shallow (<8 km) and deeper crust. We take the advantage of recent increases in seismic data coverage to build a new 3D shear wave speed model by jointly inverting Rayleigh wave ellipticity, phase velocity, and teleseismic P waveforms. In the Great Valley, the new model reveals an asymmetric basement, steeply dipping in the west and gently dipping in the east. Beneath its western margin, in the Coast Ranges, we resolve a wedge-shaped, low-velocity zone in the upper-middle crust, interpreted as Franciscan Complex. Our images confirm that uplift of the western Great Valley and an eastward shift of its depositional center are caused by wedging and underthrusting of the complex during subduction. Across the Basin and Range, the resolved crust has an average thickness of 38 km in the southern half of the northern Basin and Range, about 5 km thicker than neighboring regions. The thickened crust overlaps with major volcanic centers of the mid-Cenozoic ignimbrite flare-up. This spatial correlation may suggest magmatic intrusions and underplating contributed to crustal growth and thickening prior to Miocene Basin and Range extension. Overall, the new model is consistent with active source studies in the region but provides a more comprehensive view of shallow and deep structures across this large and tectonically complex region. Plain Language Summary Accurate velocity models provide constraints on the depth of and materials that make up shallow sedimentary basins and deep crystalline crust, and can help researchers better assess seismic hazards and related tectonic processes. Although a number of such models have been built for California and Nevada using different datasets and methods, this region lacks a self-consistent model that can accurately define both shallow (<8 km) and deep crustal features. In this study, we take advantage of a dense network of earthquake stations across these states to build a new velocity model by inverting multiple earthquake datasets to produce images of the shallow and deep crust. The new model provides a more comprehensive view of shallow and deep features across this large and tectonically complex region, and helps to elucidate their development.