2008 年 60 巻 3 号 p. 139-151
The Tokachi-oki earthquake (M=7.9) of May 16, 1968 and the Sanriku-Haruka-oki earthquake (M=7.6) of December 28, 1994 have a partially common source area and the 1968 event consists of two asperities, southern one of which took a role of asperity once again for the 1994 event. Short-period seismic wave radiation zones (SPRZs) have been evaluated for both the events from the inversion analysis of seismic intensity data. We also identified their energy centroids of all the SPRZs. It was concluded that the every centroid of SPRZ was located at the edge of corresponding asperities of the 1968 and the 1994 earthquakes in the forward direction of fault rupture. One SPRZ was located near the terminal slip points in the southern asperity for the 1968 event and was active recurrently for the 1994 event as well as asperity. We calculated magnitude m for both the SPRZs for the 1968 and the 1994 event. m from the southern SPRZ of the 1968 event was larger than that from the SPRZ of the 1994 event. This suggested that the short-period seismic wave excitation from the asperity of the multiple-segment rupture event is larger than that from the same asperity for the single-segment rupture event occurring from the same segment.