A dislocation model for the Parkfield earthquake

Abstract

Using the Haskell formulation relating the displacement time history on a fault surface to the displacement time history at a point in an infinite space, a propagating dislocation has been used to model the Parkfield, California, earthquake of June 27, 1966. Reasonable agreement is obtained with displacement from doubly integrated accelerograms using a model with a propagation velocity of 2.8 to 3.0 km/sec, displacement of 25 cm, and particle velocity at the fault of greater than 10 cm/sec. From the model, trigger times of the accelerometers can be estimated and are up to 4 sec after the first P arrivals. A high-frequency phase on the vertical accelerogram can be related to P waves originating from irregularities of the rupture process. Calculation of surface-wave arrival times shows that (1) surface waves may be important on the displacement records before body-wave arrivals ended and (2) when the observations diverge from the model, it could be due to surface waves.