Reports

Variation of P-Wave Velocity before the Bear Valley, California, Earthquake of 24 February 1972

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Science  21 Jun 1974:
Vol. 184, Issue 4143, pp. 1281-1283
DOI: 10.1126/science.184.4143.1281

Abstract

Residuals for P-wave traveltimes at a seismnograph station near Bear Valley, California, for small, precisely located local earthquakes at distances of 20 to 70 kilometers show a sharp increase of nearly 0.3 second about 2 months before a magnitude 5.0 earthquake that occurred within a few kilometers of the station. This indicates that velocity changes observed elsewhere premonitory to earthquakes, possibly related to dilatancy, occur along the central section of the San Andreas fault system.