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U.S. Geological Survey Crustal Studies Technical Letter Number 1

The Parkfield-Cholame, California, Earthquakes of June–August, 1966: Instrumental Seismic Studies

By Jerry P. Eaton


Thumbnail of and link to report PDF (35.4 MB)Abstract

U.S. Geological Survey instrumental seismic studies in the Parkfield-Cholame area consist of three related parts that were undertaken as pilot studies in a program designed to develop improved tools and concepts for investigating the properties and behavior of the San Andreas fault. These studies include:

1. The long=term monitoring of the seismic background on the San Andreas fault in Cholame Valley by means of a short-period Benioff seismograph station at Gold Hill.

2. The investigation of the geometry of the zone of aftershocks of the June 27 earthquakes by means of a small portable cluster of short-period, primarily vertical-component seismographs.

3. The seismic-refraction calibration of the region enclosing the aftershock source by means of three short reversed refraction profiles and a “calibration shot” near the epicenter of the main June 27 earthquake. This brief report outlines the work that has been completed and presents some preliminary results obtained from analysis of records from Gold Hill and the portable cluster.

  • This report is available only on the Web.

For additional information:
Contact Information, Earthquake Science Center, Menlo Park Science Center
U.S. Geological Survey
345 Middlefield Road, MS 977
Menlo Park, California 94025

This report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Eaton, J.P., 1967, The Parkfield-Cholame, California, earthquakes of June–August, 1966; instrumental seismic studies: U.S. Geological Survey Crustal Studies Technical Letter Number 1, 26 p. (Available at



Results from the Gold Hill Seismograph

Pre-Earthquake Seismic Activity

Relationships among Foreshocks, Main Shock, and Aftershocks

Frequency of Aftershocks

Record of Intense Ground Motion

Geometry of the Aftershock Source Region Southeast of Gold Hill

Seismic-Refraction Calibration of the Crust in the Aftershock Region

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