2000年鳥取県西部地震に伴う地殻変動と断層モデル

抄録

The 2000 Western Tottori Earthquake occurred on October 6, 2000, in the border of Tottori-Shimane prefectures. Japanese nationwide continuous GPS array recorded coseismic as well as postseismic crustal movements due to the earthquake. The maximum coseismic displacement observed was about 17cm. The coseismic deformation pattern clearly demonstrates a left-lateral strike slip source mechanism, which is consistent with seismic data analysis results. Leveling surveys around the focal region revealed up to 15cm vertical displacement near the source fault. GPS sites northeast of the source region were displaced up to 2cm to the northeast during 3 months after the earthquake, while a GPS site on the other side moved to the south by 2cm. Crustal deformation data are inverted to estimate two types of static fault models. One is a single rectangular fault model which can reproduce the coseismic displacement vectors observed by GPS. The other fault model, whose geometry is derived from precise re-determination of aftershocks, provides detailed information on slip distribution. We need to supplement subfaults in the shallower (depth<4km) parts to the original fault model in order to explain leveling change data, which implies systematic bias in the hypocenter depth or a full relaxation of stress by the main shock. Estimated moment magnitude were 6.6 and 6.7 for the two models, consistent with waveform inversion analysis.