1. Hawaii Institute of Geophysics and Planetology; University of Hawaii; Honolulu Hawaii 96822 USA
2. Center for Earthquake Research and Information; University of Memphis; Memphis Tennessee 38152 USA
3. Department of Earth, Atmospheric and Planetary Sciences; MIT; Cambridge Massachusetts 02139 USA
4. Instituto Geográfico Militar de Chile; Santiago Chile
5. Instituto Geográfico Militar de Argentina; Buenos Aires Argentina