1. U.S. Geological Survey, Earthquake Science Center, Pasadena, California, U.S.A.
2. U.S. Geological Survey, Albuquerque Seismological Laboratory, Albuquerque, New Mexico, U.S.A.
3. U.S. Geological Survey, Geological Hazards Science Center, Golden, Colorado, U.S.A.
4. Earthquake Research Institute, U.C. Santa Barbara, Santa Barbara, California, U.S.A.