1. R. J. Weldon and K. M. Scharer are in the Department of Geological Sciences, University of Oregon, Eugene, OR 97403, USA.
2. T. E. Fumal is with the Earthquake Hazards Team, U.S. Geological Survey, Menlo Park, CA 94025, USA.
3. G. P. Biasi is at the Seismological Laboratory, University of Nevada, Reno, NV 89557, USA.