TECTONIC HISTORY OF THE ROKKO-AWAJI ACTIVE FAULT ZONE (THE SEISMIC SOURCE FAULT OF THE 1995 SOUTHERN HYOGO PREFECTURE EARTHQUAKE)

点击翻译按钮获取中文摘要

The following major research results have been obtained. (1) The results of trench surveys show that (i) there are at least four large seismic events produced by slip on the Gosukebashi fault in the Holocene in the southeastern Rokko Mountains of Japan, they are : the youngest event is associated with the 1596 y.A.D.Keicho-Fushimi large earthquake which occurred in the area around Kyoto-Kobe City ; the second younger event is probably correlated with the 416 y.A.D.Yamato earthquake which is the oldest historic earthquake in Japanese historic records ; (ii) the horizontal displacement produced by an individual event is about 1.5 m, and the recurrence of seismic events intervals about 1,200 years in the Gosukebashi fault. (2) The Otsuki fault and Ashiya fault zone are presently active, the former having a slip-rate of about lmm/y and the latter having a slip-rate of 0.5-0.85 mm/y in vertical in the late Quaternary. (3) Foliated cataclasites which display S-C fabrics similar to those of mylonites are found in granitic rocks along the Rokko-Awaji fault zone, Japan. It is revealed clearly that the S-C cataclasites in the Rokko-Awaji fault zone formed at temperatures between 150-250 0C corresponding to depths of 5-8 kin, at a continental geothermal gradient of 30 0C/km, before being uplifted and exposed. This study of cataclastically deformed rocks shows that the fault zone theology of the upper 5-10 km of crust is greatly influenced by deformational processes in S-C cataclasites.