abstract

The instrumental epicenters of two major earthquakes in Nevada on December 16, 1954, were located approximately on fault breaks in Dixie Valley and just north of Fairview Peak. The focal depths, estimated by pP — P, were of the order of 40 and 15 km., respectively.

Times of P at distances less than 1,200 km. were found to fit a straight-line travel-time curve of slope 1/8.05 sec. per km., except that times from a group of nine stations in northern and central California and southern Nevada fell about 2 seconds below the line. These observations were interpreted in terms of regional variations in crustal thickness, with a relatively thin crust under most of California and southern Nevada, and a relatively thick crust under the intermountain states and the Sierra Nevada and White Mountains.

Travel times for P at distances greater than 14° were found to be in good agreement with tables published by Gutenberg in 1953.

Variations observed in the amplitude ratio pP/P for the Fairview Peak shock were explained in terms of direction of faulting.

The Fairview Peak earthquake provided a unique opportunity for a critical test of the seismic method for determining the direction of motion at the focus of an earthquake. The seismic solution indicated a fault striking N 11° W and dipping 62° E. Both normal and right lateral components of motion were indicated, with the lateral component about twice the normal component. The geodetic measurements agree with the seismic solution almost exactly.

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