Affiliation: | (1) Institute of Geological Sciences, SW7 2DE London, England;(2) U.S. Geological Survey, 22092 Reston, Virginia;(3) U.S. Geological Survey, 22092 Reston, Virginia;(4) Stanford Research Institute, 94025 Menlo Park;(5) Massachusetts Institute of Technology, 02139 Cambridge, Massachussetts;(6) American Embassy, La Paz, Bolivia |