BOLIVAR: Crustal Structure Across the Caribbean-South American Plate Boundary at 67.5°W: Results From Wide-Angle Seismic Data

C. A. Zelt1, M. B. Magnani1, A. Levander1, M. Schmitz2, G. L. Christeson3, P. Mann3, D. S. Sawyer1, and the BOLIVAR study group

1Rice University, Dept. Earth Science, Houston, TX 77005, United States
2Fundacion Venezolana de Investigaciones Sismologicas, Prolongacion Calle Mara, Caracas 76880, Venezuela
3University of Texas at Austin, Jackson School of Geosciences, Inst. for Geophysics, Austin, TX 78759, United States

The active-seismic component of the multi-disciplinary NSF Continental Dynamics BOLIVAR project (Broadband Ocean and Land Investigations of Venezuela and the Antilles arc Region) was completed in June, 2004. The goal of this project is to image the Caribbean-South American plate boundary and study continental growth by accretion of the Leeward Antilles island arc to the South American continent. The arc has been obliquely colliding with the passive margin of northern South America since the late Cretaceous. Motions across the plate boundary are transpressive and include right-lateral strike-slip faulting, underthrusting of Caribbean seafloor beneath the South Caribbean deformed belt, and the formation of a fold and thrust belt and adjacent foreland basin. In addition to the active-seismic studies, other workers on this project in the U.S. and Venezuela are involved in geological, geochemical and passive seismological studies.

We present preliminary results of the wide-angle data along a north-trending profile ~600 km long at 67.5°W longitude, between 8.5° to 14°N latitude. This profile extends offshore from the Venezuela basin to the fold and thrust belt onland in Venezuela. In between the profile crosses the South Caribbean deformed belt, the Aves Ridge, the Bonaire Basin, and the Oca-Moron-El Pilar fault system. High-quality multi-channel seismic reflection data were acquired along the 390 km offshore portion of the profile using the R/V Ewing (see Magnani et al., this session). The Ewing airgun shots were also recorded by 42 ocean bottoms seismometers deployed from the R/V Seward Johnson II. In addition, onshore-offshore data were acquired by recording the airgun shots using Reftek Texans at 329 stations extending from the coast to ~200 km inland. Two large land shots were also recorded by the land stations to provide reversed coverage of the onland portion of the profile. The wide-angle data and a preliminary 2-D velocity model from traveltime inversion along the 600 km profile using the OBS, onshore-offshore, and land shot data will be presented.