The Hyogoken-Nanbu Earthquake occurred in the Akashi Strait on January 17, 1995, and caused severe damage in Kobe, Nishinomiya, Ashiya, Takarazuka and the northern part of Awaji Shima Island. Immediately after the earthquake, Hydrographic Department of Japan carried out the sea bottom survey in the Osaka Bay and the Akashi Strait to reveal the distribution of faults and to detect the seafloor deformation related to the event.
The reflection survey revealed the existence of many faults in the Osaka Bay. Seismic profiles show that these faults are accompanied by the deformed Osaka Group correlated to Pleistocene. We compared these seismic profiles to the seismic records obtained in 1973 and 1974. Three active faults, one is located on the northern extension of the Nojima Fault and others are offing Tarumi and Suma, are considered to move at this time. Other faults in the Osaka bay are located outside of the aftershock area, then they are not directly related to this event.
From our reflection data, we regard the Osaka Bay Fault as A grade active fault that is active in Holocene. Further detailed survey and study should be conducted on the Osaka Bay Fault.
