Crustal thickness map of the western United States by partitioned waveform inversion

The partitioned waveform inversion method [Nolet, 1990] was used to obtain a new crustal thickness map of the western United States. We fitted 200 seismograms containing higher- and fundamental mode Rayleigh waves for events and stations in the western United States, which provided average crustal thickness constraints between each source-receiver pair. All these constraints were combined in a linear inversion to obtain a crustal thickness map. Local crustal thickness estimates from published seismic reflection/refraction work were used as additional constraints to overcome deficiencies of path coverage in some areas. The resulting crustal thickness map shows thicker (similar to 45 km) crust beneath the Cascades, thick (similar to 40 km) crust beneath the Sierra Nevada, thin (similar to 30 km) crust beneath the Basin and Range, and thick (greater than similar to 45 km) crust beneath the Colorado Plateau. The boundary between the Colorado Plateau and the southern leg of the Basin and Range is a prominent feature of the model. Thick crust is seen at the bend of the San Andreas fault near Los Angeles. Our model is broadly consistent with the crustal thickness map of Mooney and Weaver [1989]. A quantitative comparison with the crustal thickness model 3SMAC [Nataf and Ricard, 1996] was performed by inverting for a model that deviates least from it. Results show that we are able to retain most of the features of that model while maintaining a good fit to the surface wave and point constraint data.