Caracas, Venezuela
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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 | Year: 2011

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.

Rocabado V.,FUNVISIS | Schmitz M.,FUNVISIS | Hernandez J.J.,Ingenieria Sismica y Estructural | Morales C.,FUNVISIS
Revista de la Facultad de Ingenieria | Year: 2011

Under the seismic microzoning project of Caracas city, has been done since mid 90's several ambient noise measurements in order to determinate fundamentals periods of soil. In this work we showed a new relationship that includes the effect of the surface sediment layers, considering the values of shear-wave velocities for the frst 30 m (Vs30) and the value of Vs to the deepest layer. The results indicate that this relationship generates more accurate estimates of sediment thickness comparing with real values of depth; this relationship was calibrated with information from 4 depth boreholes done in Caracas, obtaining accurate depth values. The main objective for this new relationship is allow for future studies in other cities of country, had a local relationship between period and sediments thickness that considering local information of soils (Vs30 y Vs) to generate accurate sediment thickness maps from environmental noise measurements.

Padron C.,Simon Bolivar University of Venezuela | Mendes A.K.C.,FUNVISIS | Schmitz M.,FUNVISIS | Hernandez J.J.,Ingenieria Sismica y Estructural
Revista de la Facultad de Ingenieria | Year: 2011

Based on the results of Caracas Seismic Microzoning Project, carried out in the years 2005 until 2009, in which were identified zones with similar seismic response, the interest of determining how those results could support the urban planning process of the city arises. In order to contribute to the discussion over this issue, the main features of the seismic hazard, as well as other types of hazard, vulnerability aspects and the urban planning regulation frame of Chacao municipality, in which four buildings collapsed during 1967 earthquake, were studied. The study revealed that the hazard levels presented in the seismic microzonation do not rule neither establish conditions to the land use planning nor the urban design, except for economics effects, and it is a necessary improvement to the in force code for seismic-resistant buildings. The seismic microzonation, together with an appropriate urban planning and management process including structural upgrading, urban renovation, greater law enforcement and socio-technical accompaniment, could reduce significantly the seismic risk levels.

Huerta M.,Simon Bolivar University of Venezuela | Huerta M.,Salesian Polytechnic University | Huerta M.,Prometeo Project Researcher SENESCYT | Gonzalez R.,Simon Bolivar University of Venezuela | And 5 more authors.
2016 IEEE Colombian Conference on Communications and Computing, COLCOM 2016 - Conference Proceedings | Year: 2016

The versatility and low energy consumption of Wireless Sensor Networks (WSN), makes this technology a potential tool for the development of large-scale networks, where access to communication services and energy consumption present some limitation. Because of this, it becomes a potential solution for development of post-seismic alarm networks. The registration of the maximum acceleration peaks, that could be experiment by building structures after an earthquake, could be used to help to identify potentially affected areas after the occurrence of a seismic event. However, the number of message that could be generated in the network could affect the effective delivery of reported data. Because message congestion could become a critical factor that affect the successful delivery of data over the network. In this paper, is being shown a performance evaluation of a post-seismic assessment solution through different scenarios where load balancing Load-Aware On-Demand Routing (LAOR) and Flooding protocols were analyzed, as well as the use of a mechanism to desynchronize the send of messages in the network, based on the Backoff Algorithm of IEEE 802.15.4 Standard. An additional Backoff time called WT is also proposed for network desynchronization to achieve some improvement in the network QoS. The simulation results show that our proposal significantly improve performance on both protocols. The different scenarios that were evaluated considered the possibility of the collapse of some buildings after a strong or moderate magnitude event and the effect that this fact can introduce in the message traffic through the network in a seismic event conditions. © 2016 IEEE.

Audemard M. F.A.,Venezuelan Foundation for Seismological Research | Audemard M. F.A.,Central University of Venezuela | Perucca L. L.P.,Gabinete de Neotectonica y Geomorfologia | Perucca L. L.P.,CONICET | And 7 more authors.
Journal of South American Earth Sciences | Year: 2016

The Matagusanos-Maradona-Acequión Valley sits within the Andes Precordillera fold-thrust belt of western Argentina. It is an elongated topographic depression bounded by the roughly N-S trending Precordillera Central and Oriental in the San Juan Province. Moreover, it is not a piggy-back basin as we could have expected between two ranges belonging to a fold-thrust belt, but a very active tectonic corridor coinciding with a thick-skinned triangular zone, squeezed between two different tectonic domains. The two domains converge, where the Precordillera Oriental has been incorporated to the Sierras Pampeanas province, becoming the western leading edge of the west-verging broken foreland Sierras Pampeanas domain. This latter province has been in turn incorporated into the active deformation framework of the Andes back-arc at these latitudes as a result of enhanced coupling between the converging plates due to the subduction of the Juan Fernández ridge that flattens the Nazca slab under the South American continent.This study focuses on the neotectonics of the southern tip of this N-S elongated depression, known as Acequión (from the homonym river that crosses the area), between the Del Agua and Los Pozos rivers. This depression dies out against the transversely oriented Precordillera Sur, which exhibits a similar tectonic style as Precordillera Occidental and Central (east-verging fold-thrust belt). This contribution brings supporting evidence of the ongoing deformation during the Late Pleistocene and Holocene of the triangular zone bounded between the two leading and converging edges of Precordillera Central and Oriental thrust fronts, recorded in a multi-episodic lake sequence of the Acequión and Nikes rivers. The herein gathered evidence comprise Late Pleistocene-Holocene landforms of active thrusting, fault kinematics (micro-tectonic) data and outcrop-scale (meso-tectonic) faulting and folding of recent lake and alluvial sequences. In addition, seismically-induced effects already reported in the literature by this working team further support the tectonic activity of neighboring faults in the Holocene. As a concluding remark we could state that the ongoing deformation in the region under study is driven by a compressional regime whose maximum horizontal stress in the late Pleistocene-Holocene is roughly east-west oriented. This is further supported by focal mechanism solutions. © 2016.

Masy J.,Rice University | Niu F.,Rice University | Niu F.,China University of Petroleum - Beijing | Levander A.,Rice University | Schmitz M.,FUNVISIS
Earth and Planetary Science Letters | Year: 2015

We have combined surface wave tomography with Ps and Sp receiver-function images based on common-conversion-point (CCP) stacking to study the upper mantle velocity structure, particularly the lithosphere-asthenosphere boundary (LAB), beneath eastern and central Venezuela. Rayleigh phase velocities in the frequency range of 0.01-0.05 Hz (20-100 s in period) were measured using the two-plane-wave method and finite-frequency kernels, and then inverted on a 0.5°. ×. 0.5° grid. The phase velocity dispersion data at grid points were inverted for 1D shear velocity profiles using initial crust-mantle velocity models constructed from previous studies. The 3D velocity model and receiver-function images were interpreted jointly to determine the depth of the LAB and other upper mantle features. The tomographic images revealed two high velocity anomalies extending to more than ~200 km depth. One corresponds to the top of the subducting Atlantic plate beneath the Serrania del Interior. The other anomaly is a highly localized feature beneath the Maturin Basin. The LAB depth varies significantly in the study region: It is located at ~110 km depth beneath the Guayana Shield, and reaches ~130 km at the northern edge of the Maturin Basin, which might be related to the downward flexural bending due to thrust loading of the Caribbean plate and pull from the subducting Atlantic plate. Immediately to the west, the lithosphere is thin (~50-60 km) along the NE-SW trending Espino Graben from the Cariaco basin to the Orinoco River at the northern edge of the craton. The LAB in this region is the top of a pronounced low velocity zone. Westward, the lithosphere deepens to ~80 km depth beneath the Barinas Apure Basin, and to ~90 km beneath the Neogene Merida Andes and Maracaibo block. Both upper mantle velocity structure and lithosphere thickness correlate well with surface geology and are consistent with northern South American tectonics. © 2014 Elsevier B.V.

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 | Year: 2010

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.

Lopez O.A.,Central University of Venezuela | Coronel G.D.,Central University of Venezuela | Rojas R.,FUNVISIS
Revista de la Facultad de Ingenieria | Year: 2014

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.

Sanchez J.,University of Kiel | Gotze H.-J.,University of Kiel | Schmitz M.,FUNVISIS
International Journal of Earth Sciences | Year: 2011

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.

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 | Year: 2015

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.

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