1. U.S. Geological Survey, California Volcano Observatory, Moffett Field, CA, USA.
2. U.S. Geological Survey, Hawaiian Volcano Observatory, Hilo, HI, USA.
3. Department of Statistics and Applied Probability, University of California, Santa Barbara, CA, USA.
4. Department of Geophysics, Stanford University, Stanford, CA, USA.
5. U.S. Geological Survey, Cascades Volcano Observatory Vancouver, WA, USA.