1. Department of Earth and Environmental Sciences, University of Iowa , Iowa City, IA 52242 , USA
2. Department of Earth & Planetary Sciences, University of California Santa Cruz , Santa Cruz, CA 95064 , USA
3. U.S. Geological Survey, Earthquake Hazards Program , Golden, CO 80401 , USA
4. Department of Earth Sciences, University of Oregon , Eugene, OR 97403 , USA