Seismology, geology, and geotechnical issues

The Hyogoken-Nanbu (Kobe) earthquake of January 17, 1995 (5:46:52 JST) occurred in an area of complex faulting located near Awaji Island and the Hanshin area of Japan (34.607 N, 135.043 E, depth 14.3 km; Japan Meteorological Agency, JMA). The area which is near the urban centers of Kobe City and Osaka is located about 250 km from the Nankai trough, which forms the boundary between the Philippine Sea and Eurasian plates (Figure 2.1.1). The earthquake of magnitude 7.2 (JMA) is the most severe earthquake to affect the region this century. The largest previous earthquake near Kobe City was a magnitude 6.1 which occurred in 1916 on or near the same fault. Other large but distant earthquakes occurred in 1944 and 1946 along the plate boundary (Figure 2.1.1). Numerous faults known to be active in the Quaternary extend throughout the affected region (Figure 2.1.2). However, prior to January 17, 1995 the area was characterized by relatively low seismicity compared with areas near the plate boundaries (Figure 2.1.1). This 1995 earthquake having occurred at considerable distance from the plate margin, can be considered an intraplate event.