1974年伊豆半島沖地震の破壊過程

抄録

The 1974 Izu-Hanto-Oki earthquake is studied in detail using near-field strong motion seismograms. A waveform inversion method is applied to deduce the dislocation distribution and the characteristics of the rupture propagation during this earthquake.
This earthquake involved right-lateral strike-slip motion on the almost vertical fault plane with a strike of N47°W. The rupture initiated at the central deepest part of the fault plane and propagated both sides smoothly, as a bilateral rupture propagation. The total source process time is about 11sec. A dislocation larger than 1m occurred in the region ranging from 3km to 10km in depth, and its horizontal span is about 20km around the hypocenter. Except for the southeastern end of the fault plane, dislocation smaller than 0.5m occurred in the shallower region of the fault plane. The average dislocation on the whole fault plane is 1.0m, and the total seismic moment is 7.6×10²⁵dyne·cm. Few aftershocks took place in the area where dislocation larger than 2m occurred during the main event. Surface fractures, associated with this earthquake, appeared in the meizoseismal area. The dislocation distribution seismologically obtained in this study is consistent with the fault displacement along these surface fractures.