1. Associate Professor, Civil and Environmental Engineering, Univ. of Nevada, Las Vegas, NV 89154-4015. E-mail: bluke@egr.unlv.edu
2. Seismologist, GX Technology, 2101 City West Blvd., Bldg. 3, Ste. 900, Houston, TX 77042; formerly, Instituto Mexicano del Petróleo, Mexico City. E-mail: ccalderon@gxt.com