兵庫県南部地震震源域におけるクーロン破壊関数の時間変化のシミュレーション
特集: 大地震の長期予測はどこまで可能か? V. 総合評価と地殻活動予測モデル
1998 年 50 巻 appendix 号 p. 229-249
詳細
1998 年 50 巻 appendix 号 p. 229-249
We synthesize temporal variation in Coulomb Failure Functions (CFF) for the mechanism similar to the 1995 Hyogo-ken Nanbu earthquake taking both interseismic stress loading and coseismic changes due to large events into account. A block-fault model derived from the inversion of triangulation and trilateration data during 100 years by HASHIMOTO and JACKSON (1993) is adopted as the model for interseismic loading. Temporal changes in CFF is calculated as a sum of secular changes for back slip of block boundary faults in their model during arbitrary period since 1855 and coseismic changes due to large events which occurred during the corresponding period with simple pure elastic dislocation model. Among the several factors which affect CFF change in the source region of the 1995 Hyogo-ken Nanbu earthquake, increasing back slip of faults along the Nankai trough, which may represent strengthening of coupling, decreases CFF for right-lateral strike-slip mechanism on NESW trending vertical faults by 0.2 MPa/100yr at (34.6°N, 135.04°E and 10 km deep). Back slip along the Arima-Takatsuki Tectonic Line and Rokko fault system increase CFF most (1.6 MPa/100yr), though the calculated point is closely located to the edge of modeled block-boundary fault. These calculations seem contradictory to the hypothesis that strengthening of coupling between the subducting Philippine Sea plate and the Japanese islands induces the activity of large inland events. Loading of locked part due to stable sliding of deeper part of block boundary faults may play a main role for the accumulation of stress. Among large events, the 1946 Nankaido earthquake may have caused eminently large increase in CFF (0.1 MPa) near the epicenter of the Hyogo-ken Nanbu earthquake. The 1944 Tanankai earthquake may have increased CFF by about 0.01 MPa, but the 1927 Tango earthquake decreased it by 0.02 MPa. Other events may not have larger effect than 0.01 MPa. Summing up these contributions, our results suggest that the CFF for the Hyogo-ken Nanbu earthquake increased larger than 2 MPa since 1855.
