BOLIVAR: Onshore observations of land and sea seismic sources in northern Venezuela

M. Schmitz*, V. Rocabado*, J. Sanchez*, V. Cano*, R. Ollarves*, M. Bezada*, J. Avila*, E. Vieira*, M. Yanez*, A. Levander (713-348-6064), C. Zelt (713-348-4757) and BOLIVAR active seismic working group (*FUNVISIS, Caracas, Venezuela; +Earth Science, Rice University, 6100 Main Street, Houston, Texas, 77005 USA).

Within the framework of the BOLIVAR and GEODINOS(define acronym) projects, active seismic measurements were made during the months of April and May 2004 in northern Venezuela between 64° and 70° W. Four deep seismic reflection and refraction profiles were acquired perpendicular to the Caribbean-South America CAR-SA) plate boundary. To the north, a complex plate plate boundary zone is marked by the Oca-Ancon, San Sebastian and El Pilar fault zones, a 1000 km long dextral strike-slip fault system, which accommodates a relative movement of 2 cm/year between CAR-SA. From the Caribbean Mountain System in the north, the seismic profiles run into the exhumed Falcon Basin in the west and the foreland Guarico and Oriental Basins in central and eastern Venezuela, divided by Frontal Thrust Systems from the Caribbean Mountain System. Further south, the Guayana Craton corresponds to stable SA. Up to now, little has been known about the crystalline crustal structure. In western Venezuela, the overall crustal thickness decreases from 45 km in the crato to ~35 km along the coastline.

Air gun shots from the marine refraction lines, recorded by the broadband stations of the Venezuelan national seismic network as well as the BOLIVAR project PASSCAL broadband network, were used to build seismic sections in which first arrivals can be observed to offsets greater than 200 km. This data will be modeled and interpreted using two different approaches: 2D modeling using the RAYINVR package and 3D tomography using the FAST package. Along the four main profiles, 2 land shots with chemical explosions were fired on each profile in order to provide information on the crustal and upper mantle structures. Data quality is good for the land shots to at least 200 km distance from shotpoints. The data will provide information on the crust and mantle structure in the plate boundary region to the northern edge of the South American craton. Contribution to project G-2002000478.