Resumen

KANTAK, PETER; SCHMITZ, MICHAEL  y  AUDEMARD, FRANCK. Sediment Thickness and a WEST-EAST Geologic Cross Section in the Caracas Valley. Rev. Fac. Ing. UCV [online]. 2005, vol.20, n.4, pp.85-98. ISSN 0798-4065.

Caracas is located at the Caribbean - South America plate boundary zone, with an associated strike slip fault system, which accommodates the relative movement of both plates and is responsible for the seismic hazard in the region. The damage pattern of the 1967 Caracas earthquake emphasized the existence of important site effects due to the sedimentary basin fill of the Caracas valley. A revised map of the sedimentary thickness was developed during this study, based on drill holes (mostly from water exploration) and results of seismic refraction investigations. A local depression in the area of Los Palos Grandes / Santa Eduvigis with exceptionally high values of more than 300 m could be confirmed by the available data. The shape of the depression seems to be controlled by NW - SE striking tectonic features rather than east-west striking features, as suggested by previous compilations. The second most important depth of the valley fill, in San Bernardino, reaches 140 m, while sediment thickness in the remaining areas does not exceed 80m. The east-west geological cross section through Caracas valley (along Metro line 1) permits the recognition of the four main lithological units of the Quaternary sediments: alluvial fan deposits, which can be subdivided into a proximal and a distal facies, terrace deposits of the Guaire River, and lacustrine floodplain deposits originated in buildups of Guaire River and its tributaries. The classification of the sediments for seismic microzoning purposes is supported by local seismic refraction studies, which give information on the velocity structure of the uppermost sedimentary strata.

Palabras clave : Caracas; alluvial sediments; seismic microzoning,; seismic refraction; GIS.