抄録
The seismic acceleration recorded at the Parkfield, Cholame No.2 station in California at the time of the Parkfield earthquake of June 28, 1966, is analysed to determine the focal parameters on the dynamical process of faulting.
A direct comparison of the calculated accelerations with the recorded one yields focal parameter estimates of 0.5-0.7sec for the rise time of the source time function, 50-70cm for the average dislocation and 50cm/sec for the particle velocity of the fault motion. The effective stress is determined from the particle velocity to be 25-50bars by the dynamic faulting models recently developed. The wave form of the calculated acceleration shows a good peak-to-peak correspondence with the recorded one, only when the source time function is assumed to be of a ramp type. This suggests that the ramp function is a good approximation for the source time function of this earthquake.
We obtain an amplitude of about 7cm for the perpendicular component of the theoretical ground displacement if the values of 50-70cm for the average dislocation and of 0.5-0.7sec for the rise time as estimated above are used. The value of 30cm for the amplitude of displacement, obtained by previous investigators from numerical integration of the record acceleration, seems to be too large. The integrated displacements may not be good approximations for the true ground displacements.
