Tomography of the Source Area of the 1995 Kobe Earthquake: Evidence for Fluids at the Hypocenter?
Seismic tomography revealed a low seismic velocity (-5%) and high Poisson's ratio (+6%) anomaly covering about 300 square kilometers at the hypocenter of the 17 January 1995, magnitude 7.2, Kobe earthquake in Japan. This anomaly may be due to an overpressurized, fluid-filled, fractured rock matrix that contributed to the initiation of the Kobe earthquake.
© 1996 American Association for the Advancement of Science. Received 4 September 1996; accepted 19 November 1996. We are grateful to the members of the Urgent Observation Group for the 1995 Hyogo-Ken Nanbu Earthquake, who operated the portable stations and picked the P- and S-wave arrival times, and to the staff members of the seismic networks of Kyoto University, Nagoya University, Kochi University, Kyushu University, and the University of Tokyo for providing the data recorded by their permanent networks that were used in this study. J. Vidale and an anonymous referee provided thoughtful reviews, which improved the manuscript. This work was partially supported by a grant from the National Science Foundation (EAR-9526810) to D. Zhao. This paper is Contribution 5785, Division of Geological and Planetary Sciences, California Institute of Technology.