Detailed crustal structure beneath the Southern Sierra Nevada Region: Refraction/wide-angle reflection P-wave modeling

by S D Ruppert (LLNL), M Fliedner (Stanford University), and K Miller (UTEP)

Three seismic refraction/wide-angle reflection profiles were collected as part of the Southern Sierra Nevada Continental Dynamics Project's multi-disciplinary investigation of Sierra Nevada/Basin & Range lithosphere. 3-D travel time analysis reveals a small asymmetric crustal root (8-10 km of thickening) beneath the south-central Sierras and 10-15 km of thickening beneath the central Sierras. This northward thickening root extends eastward beneath the White Mountains and adjacent Basin & Range. The seismic profiles included: (1) a 325-km-long north-south profile extending from near Mono Lake southward through Owens Valley to the Garlock fault, (2) a 400-km-long east-west profile, extending from Death Valley to the San Andreas Fault, and (3) a 480-km-long east- west profile from the NPE, a 1-kt-unreversed shot, recorded from Beatty, Nevada nearly to the Pacific coast. Nominal shot and receiver spacing were 50 km and 500 m, respectively. Seismic models, constructed from both inline and fan shots along these profiles show that the small crustal root (crustal thicknesses of 38-42 km) is centered beneath the highest elevations of the Sierra Nevada Range along the east-west profile and increases to 42-48 km northward while thinning to 35-38 km southward. Mid-crustal velocities beneath the Sierras and Basin & Range are 6.2-6.5 km/s down to 20 km depth, while a 6.8-7.2 km/s westward dipping wedge of ophiolite is imaged beneath the central Great Valley. Along the north-south profile, crustal thicknesses south of Owens Lake range from 28-30 km while north of Owens Lake a thicker 36-38 km crust is observed between the Sierras and the White Mountains.

Work performed under the auspices of the U.S. DOE by LLNL under contract W-7405-ENG-48.