Abstract

In 1962 a series of reversed seismic-refraction profiles was established over a line 454 km long between Eureka, Nevada, and Boise, Idaho; and additional recordings of nuclear events at the Nevada Test Site were made along the profile to southern Idaho. Shot points for the reversed profiles were located near Eureka, Elko, and Mountain City, Nevada, and near Bruneau and Boise, Idaho.

Interpretation of the refracted and reflected P events indicates: (1) The crust in the northern Basin and Range province consists of a 6.0-km/sec layer 19–24 km thick above a 6.7-km/sec layer 10–12 km thick. (2) Both the crust as a whole and the 6.7-km/ sec layer thicken abruptly at the boundary between the northern Basin and Range province and the western Snake River Plain. The 6.0-km/sec layer thins across this boundary and may be absent under the Snake River Plain. (3) The crust in the western Snake River Plain consists of a 5.2-km/sec layer 8–10 km thick over a 6.7-km/sec layer 33–38 km thick. (4) The upper mantle under both the northern Basin and Range province and the western Snake River Plain has a P velocity of about 7.9 km/ sec. Amplitudes of Pn decrease with the inverse third power of distance and indicate that the upper mantle consists of highly absorptive material or contains a low-velocity layer immediately below the M discontinuity.

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