Imaging the source area of the 1995 southern Hyogo (Kobe) earthquake (M7.3) using double-difference tomography

To understand the generation process of inland earthquake, we determined the seismic velocity structure in and around the source area of the 1995 southern Hyogo (Kobe) earthquake (M7.3) in SW Japan. We adopted the double-difference (DD) tomography method [Zhang, H. and C. Thurber. Double-Difference Tomography: the method and its application to the Hayward Fault,California. Bull Seism Soc Am 93 (2003) 1875-1889.]. We inverted arrival times recorded by a dense temporary seismic network for aftershocks and seismic networks routinely operated by Japanese Universities. Obtained results are summarized as follows: (1) Low-velocity zones of a few kilometers' width are distributed along the fault or along the aftershock alignment, suggesting that the fault of the 1995 earthquake is located primarily in a low-velocity zone. (2) Amount of velocity decrease within this low-velocity zone varies along the strike of the fault. Most of large slip areas (asperities) seem to correspond to higher velocity areas relative to the surroundings on the fault, rather than to lower velocity areas.