1. 1U.S. Geological Survey, Earthquake Science Center, Moffett Field, California, U.S.A.
2. 2California Institute of Technology, Pasadena, California, U.S.A.
3. 3U.S. Geological Survey, Earthquake Science Center, Pasadena, California, U.S.A.
4. 4Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, UC San Diego, La Jolla, California, U.S.A.
5. 5U.S. Geological Survey, Earthquake Science Center, University of Washington, Seattle, Washington, U.S.A.
6. 6Department of Seismology and Tsunami Research, Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Ibaraki, Japan