1. Seismological Laboratory 252-21, California Institute of Technology, Pasadena, CA 91125, USA. Earthquake Geology Group at the Southern California Earthquake Center, University of Southern California, Los Angeles, CA 90089, USA.
2. Department of Geological Sciences, San Diego State University, San Diego, CA 92182, USA. Earthquake Geology Group at the Southern California Earthquake Center, University of Southern California, Los Angeles, CA 90089, USA.
3. Department of Geological Sciences, Oregon State University, Corvallis, OR 97331, USA. Earthquake Geology Group at the Southern California Earthquake Center, University of Southern California, Los Angeles, CA 90089, USA.
4. E & P Technology Department, Texaco, Houston, TX 77042, USA. Earthquake Geology Group at the Southern California Earthquake Center, University of Southern California, Los Angeles, CA 90089, USA.
5. Department of Geological and Geophysical Sciences, Princeton Univesity, Princeton, NJ 08544, USA. Earthquake Geology Group at the Southern California Earthquake Center, University of Southern California, Los Angeles, CA 90089, USA.
6. Leighton and Associates, Irvine, CA 92714, USA. Earthquake Geology Group at the Southern California Earthquake Center, University of Southern California, Los Angeles, CA 90089, USA.