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Lopez O.,Central University of Venezuela | Marinilli A.,Central University of Venezuela | Bonilla R.,Central University of Venezuela | Fernandez N.,Central University of Venezuela | And 4 more authors.
Revista de la Facultad de Ingenieria | Year: 2010

This paper describes the methodology and results obtained to date in a program aiming to evaluate and reduce the risk of existing schools in Venezuela. Seventy percent of the approximately 28,000 Venezuelan schools are in high seismic hazard regions. About 46% of the 18,685 schools identified and incorporated into a geographical information system were built with old codes that do not satisfy the seismic requirements implied in current codes. A building built according to the 1955 code would resist on average a seismic motion that is about three times less intense than one built with modern codes. A total of 586 school buildings belong to three structural types of high vulnerability; 479 of these are similar or equal to the ones that collapsed in Cariaco during the 1997 earthquake. An instrument for the rapid inspection and evaluation of the vulnerability of schools was developed and applied to 131 buildings. Ten schools were selected as pilot projects for seismic retrofitting. Auxiliary structures are proposed to support most of the seismic loads, connected to the existing building by the floor slabs acting as diaphragms and supported by new foundations; drift demands are kept below 0.7% to protect the capacity of the existing structure to support gravity loads. The dynamic properties of the selected schools were determined from environment vibration tests, which will be repeated after retrofitting; four schools in the Sucre State were selected for the permanent installation of sensors to record their response to future earthquakes.

Sanchez-Rojas J.,University of Kiel | Palma M.,FUNVISIS Fundacion Venezolana de Investigaciones Sismologicas
Tectonophysics | Year: 2014

This paper presents a three-dimensional (3-D) interpretation of new gravity and seismicity datasets for northern South America. A 3-D forward density model was constructed on the basis of deep wide-angle seismic refraction sections, Moho depth from receiver functions, and surface geology. Density values were estimated from published borehole data for sediments by using empirical velocity-density functions and considering mineralogical-chemical composition variations under typical pressure-temperature conditions for upper and lower crustal rocks. The modeled 3-D density structure was kept as simple as possible. The continental and oceanic plates were formed by two sedimentary bodies, one crustal body, and one mantle lithosphere body overlying a sub-lithospheric mantle. The Caribbean plate was modeled with an atypical crustal thickness of ~. 18. km (including sediments). The geometry of the Caribbean plate was modeled using a combination of gravity modeling and analyses of the seismicity and focal-mechanism solutions. Intermediate seismicity and the orientation of the T-axes appeared aligned along the predicted position of the slab. As a result, the estimated slab dip angle under Maracaibo and the Mérida Andes was ~. 15° and increases up to ~. 20° after 100. km depth. The model shows two orientations in the slab strike: ~. N150°E. ±. 5 in western Colombia and southward underneath the Maracaibo block. The modeling results suggest that the northern South American upper and lower crusts are relatively light and the density of the Caribbean crust is typical for an oceanic crust. © 2014 Elsevier B.V..

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