[1] Brown Univ, Dept Geol Sci, Providence, RI 02912 USA
[2] Univ Calif Santa Cruz, Santa Cruz, CA 95064 USA
[3] Lamont Doherty Earth Observ, Palisades, NY 10964 USA
[4] Boise State Univ, Ctr Geophys Invest Shallow Subsurface, Boise, ID 83725 USA
[5] Oregon State Univ, Corvallis, OR 97331 USA
[6] Univ So Calif, Los Angeles, CA 90089 USA
[7] Ctr Invest Cient & Educ Super Ensenada, Ensenada 22860, Baja California, Mexico