f Surface-wave Tomographic Inversion of the South American Lithosphere (The SISAL Project)

We are studying the dispersion characteristics (measurements of group velocity) of broad band (15-2oosec) Rayleigh and Love waves propagating across the South American continent and adjacent oceans. The ultimate purpose is to invert for a high resolution, tectonic scale (lateral:5ookm) crustal and lithospheric model covering the South American, Cocos, Caribbean, Nazca and Scotia plates to depths of approximately 200 km. To date, data from more than 400 events have been analyzed yielding in excess of 4100 paths across the continent and neighboring regions. These measured group velocities are summarized in the form of tomographic maps for group velocities of Love and Rayleigh waves with periods ranging from 20 to 150 sec. We report the results of a resolution analysis (checker-board test) for a variety of periods for both Rayleigh and Love waves. The estimated group velocity maps are compared with those predicted from a recent model in which the crust is CRUST-5.1 (Mooney et. al., 1996) and the mantle is S16B30 of Masters et.al., (1996).