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Caracas, Venezuela

Lopez O.A.,Central University of Venezuela | Coronel G.D.,Central University of Venezuela | Rojas R.,FUNVISIS
Revista de la Facultad de Ingenieria

A procedure for the allocation of vulnerability, risk and seismic prioritization indices of a large number of existing buildings, located anywhere in Venezuela, is presented. The indices are calculated from basic information obtained from a short duration visit and inspection to the building. The prioritization index is determined from the product of the of hazard, vulnerability and importance indices which considers the building use and the number of occupants. The procedure takes into account typical construction types of the country including popular housing and incorporates the experiences of the destructive earthquakes of Caracas in 1967 and Cariaco in 1997. For buildings located in the Metropolitan Area of Caracas, the proposed procedure takes into account the seismic micro zoning of the city. The results of the implementation of the proposed procedure are used to select those critical buildings that require more detailed structural evaluations and support decisions toward an integrated management of seismic risk. The procedure application is illustrated in a group of 154 buildings located in a county of Caracas. Source

Bezada M.J.,Rice University | Magnani M.B.,University of Memphis | Zelt C.A.,Rice University | Schmitz M.,FUNVISIS | Levander A.,Rice University
Journal of Geophysical Research: Solid Earth

We present the results of the analysis of new wide-angle seismic data across the Caribbean-South American plate boundary in eastern Venezuela at about 65W. The ∼500 km long profile crosses the boundary in one of the few regions dominated by extensional structures, as most of the southeastern Caribbean margin is characterized by the presence of fold and thrust belts. A combination of first-arrival traveltime inversion and simultaneous inversion of PmP and Pn arrivals was used to develop a P wave velocity model of the crust and the uppermost mantle. At the main strike-slip fault system, we image the Cariaco Trough, a major pull-apart basin along the plate boundary. The crust under the Southern Caribbean Deformed Belt exhibits a thickness of ∼15 km, suggesting that the Caribbean Large Igneous Province extends to this part of the Caribbean plate. The velocity structures of basement highs and offshore sedimentary basins imaged by the profile are comparable to those of features found in other parts of the margin, suggesting similarities in their tectonic history. We do not image an abrupt change in Moho depth or velocity structure across the main strike-slip system, as has been observed elsewhere along the margin. It is possible that a terrane of Caribbean island arc origin was accreted to South America at this site and was subsequently bisected by the strike-slip fault system. The crust under the continental portion of the profile is thinner than observed elsewhere along the margin, possibly as a result of thinning during Jurassic rifting. Copyright 2010 by the American Geophysical Union. Source

Sanchez J.,University of Kiel | Gotze H.-J.,University of Kiel | Schmitz M.,FUNVISIS
International Journal of Earth Sciences

A 3-D structural model of the Caribbean-South American plate boundary was constructed by gravity modeling. The model was constrained by four wide-angle seismic refraction sections, Moho depth estimations from receiver functions, and additionally seismological hypocenters, surface geology, and geodynamic information. Density values were calculated from empirical velocity-density functions, and mineralogical-chemical composition considering specific P/T conditions. We tested different structural models for Western and Eastern Venezuela. In the final model, the fit of the measured and modeled gravity fields for a long Caribbean slab in Western Venezuela was better than the fit obtained for a short one. This interpretation is consistent with the constraining data. The slab is interpreted to extend further to the south beneath Northern Colombia and culminates in the area of the seismic cluster of the Bucaramanga nest. The modeling estimates a slab dip angle under Maracaibo and Mérida Andes of 15°, which increases to 32° below 100 km depth. The dip direction of approx. N150°E ± 5 increases lightly eastward. In Eastern Venezuela, considering its short wavelength, lineaments analyzed from gravity data (by curvature methods and Euler deconvolution) seem to be related to shallow structures and density contrast in the Serranía del Interior and not from a deep detached slab beneath the continental crust. It is deduced from modeling results that this slab configuration has a very small influence on the gravity field. The slab was modeled according to the subduction-transform propagation model with purely westward subduction and a slab break off along a vertical dip-slip tear through the lithosphere. © 2010 Springer-Verlag. Source

Alvarado M.,University of Los Andes, Venezuela | Cantos G.,University of Los Andes, Venezuela | Perez E.,University of Los Andes, Venezuela | Audemard F.,FUNVISIS
Boletin de Geologia

The Boconó fault is the most important and distinctive geological feature of western Venezuela. It runs for more than 500 km in the southeast-northwest direction with significant implication on the complex structure of the venezuelan Andes. Between the towns of Tabay and La Toma of Mérida state, it have been identified some segments of the fault parallel to the valley of Chama river. The overall geometry is rectilinear with the Chama basin located over the trace of the fault. This work attempts to describe the persistence and consistence of the geomorphological traits that have been produced by the most recent fault movements. Making use of the available aerial photography (scale: 1:25.000, 1:35.000 and 1:40.000) and field assessment, it was found that throughout much of the trace, the Boconó fault has a dextral strike-slip movement with a normal component. In particular, at southeast of Tabay town, it was observed that a fault segment, coming from the southwest, ends in a remarkable pressure ridge. It was also corroborated in Mucuchies town, a pull-apart basin due to the fact that the fault changes its pathway clockwise. Source

Hernandez J.J.,Ingenieria Sismica y Estructural | Schmitz M.,FUNVISIS | Delavaud E.,University of Potsdam | Cadet H.,LGIT Grenoble | Dominguez J.,FUNVISIS
Revista de la Facultad de Ingenieria

Elastic response spectra were developed within the purposes of the Caracas Seismic Microzoning Project, on microzones of the Caracas Metropolitan Area, including detailed site effects to improve the seismic design, overcoming the code spectra. As its core an 1D site response parametric study was performed, as function of shallow ground stiffness and sediment thickness, relying on a local seismic hazard study, the geophysical deposit model and a particular geotechnical model as inputs. The spectra were grouped and validated by means of actual earthquake records, doing small corrections. Basin effects were added from a 2D response study of the area of the valley with larger sediments, undergone to 1967 earthquake, and were extended by means of a 3D study of seismic amplifications in the valley. 2D topographical effects were also estimated. We defined macrozones of diverse seismic hazard and microzones according to shallow ground, deposits and slopes, obtaining expected mean spectra with 1D-2D effects for them, valid for common constructions, which are smoothed for using in structural engineering; then modifications are added for essential and massive constructions. Source

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