SEMI-EMPIRICAL ESTIMATION OF STRONG GROUND MOTIONS DURING LARGE EARTHQUAKES.

A synthesis method is developed for estimating deterministically strong motions during the main shock, using the records of small events such as foreshocks and aftershocks which occurred within the area of the main-shock fault. This synthesis formulation is based on a kinematic source model of Haskell type and the similarity law of earthquakes. The parameters for this synthesis are found to be consistent with the scaling relations between the moments and the fault parameters such as the fault length, width and dislocation rise time. If the ratio of the main-shock moment Mo to a small event, Mo//e, is assumed to be N**3, then the main-shock fault can be divided into N multiplied by N elements, each dimension of which is consistent with that of the small event and N events at each element may be superposed with a specific time delay to correct the difference in the rise time between the main-shock and the small event and to keep a constant slip velocity between them. By means of this method, the main-shock velocity motions were synthesized using the small-event records obtained by velocity-type strong-motion seismographs for the 1980 Izu-Hanto-Toho-Oki earthquake (M equals 6. 7). The resultant synthesized motions show good agreement with the observed ones in the frequency range lower than 1 Hz.