Strain Steps and the Dislocation Fault Model

Abstract

Strain steps associated with earthquakes ranging in magnitude from 3.2 to 7.9 have been observed at the Iwakura, Amagase and Donzurubo Observatories using super-invar bar extensometers. The stability of these instruments for vibration was confirmed by two methods. The amplitude of strain step depends on distance proportionately with R^-2.4, and based on certain assumptions, fault length seems to be related to earthquake magnitude according to following formula: M=2.2 log L -8.4 where L is the fault length in cm. Furthermore, observed values of strain steps associated with earthquakes of comparatively small magnitude (M=3.2～5.6) occurring in the northern part of the Kinki district have been compared with the residual strain fields calculated by F. Press in 1965.