1. Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, Houston, Texas 77005 U.S.A., niu@rice.edu
2. Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University, Furucho, Chikusa, Nagoya 464‐8601, Japan, kyamaoka@seis.nagoya-u.ac.jp