Abstract

Isoseismalsare drawn and field intensities listed for the Niles earthquake of May 16, 1933. The epicenter is placed at 37° 38′ N, 121° 57′ W. Isoseismals are drawn and field intensities listed for the Parkfield earthquakes of June 7, 1934. The epicenter of the shock at 8h 48mp.m. (P.S.T.) is placed at 35° 56′ N, 120° 29′ W. The epicenter of the shock at 8h 30m is placed about 4 km. north of this. Travel-time curves are drawn for each of these three shocks. It is shown that the Owens Valley stations, Tinemaha and Haiwee, did not record the normal P (v = 8.0 km/sec., ca.) for any of these earthquakes. It is concluded that there exists some barrier to these waves under the Great Valley of California (or possibly under the Sierra), which prevents their observation at stations so close to the valley as Tinemaha and Haiwee when the source is in the Coast Range region. The interpretation of the data of difficult, but there is some evidence for identifying P waves traveling through three successive layers of the earth's crust. A tentative computation of this structure is made.

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