Instrumental measurement of slippage on the Hayward fault

Abstract

A differential transformer has been used as a displacementmeter across a crack in a culvert under the Memorial Stadium, UC Berkeley. The crack is believed to be the result of progressive right-lateral slippage in recent years along the Hayward fault which traverses the stadium. The displacementmeter recorded continuous right-lateral slippage from October 7, 1965 to January 9, 1966. The average rate of movement would amount to about 0.21 inches per year. Variations in the measured displacement show no significant correlation with the present occurrence of small local earthquakes. A physical model of the observed fault slippage is outlined, based on the strain-release-by-rupture theory for the origin of shallow earthquakes. The model predicts that strain in the crystalline basement along the fault zone may be accumulating.