震央域強震記録における顕著な相に着目した1979年 Imperial 渓谷地震の多重震源性に関する解析

抄録

An analysis of identifying the multiple rupture process of the 1979 Imperial Valley, California earthquake is made utilizing distinct phases in the near-field horizontal accelerograms. Two methods are employed in the identification of the distinct phases; one is the visual inspection method and the other the quantitative method. The location of the source corresponding to the distinct phases is determined using the S-wave travel time curve. It is found that the earthquake is a multiple event with three smaller events in the period of less than 1 to 2 seconds and that the main energy is released from a localized portion about 8 to 13 kilometers from the epicenter to northwest along the fault. The results are compared with the spatial dislocation model of this earthquake obtained by Hartzell and Helmberger.