Crustal structure from San Francisco, California, to Eureka, Nevada, from seismic-refraction measurements

Seismic-refraction measurements from chemical explosions near San Francisco, California, and Fallon and Eureka, Nevada, were made along a line extending nearly 700 km inland from San Francisco across the Coast Ranges, Great Valley, Sierra Nevada, and Basin and Range Province. The velocity of P_g in the Basin and Range Province was found to be 6.0 km/sec. Between Fallon and Eureka the velocity of P_n is 7.8 km/sec, and just east of the Sierra Nevada it is about 7.9 km/sec. Two prominent phases closely following the first arrival between 50 and 250 km from the source in the Basin and Range Province were interpreted as reflections from an intermediate layer and from the Mohorovicic discontinuity. The velocity of P in the possible intermediate layer, deduced from the reflected phases be cause the refracted wave expected from this layer is nowhere a first arrival, seems to be 6.6 km/sec at the top of the layer and probably increases with depth.