Venezuelan Foundation for Seismological Research FUNVISIS

Caracas A, Venezuela

Venezuelan Foundation for Seismological Research FUNVISIS

Caracas A, Venezuela
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Aguilar I.,University of Savoy | Aguilar I.,Venezuelan Foundation for Seismological Research FUNVISIS | Beck C.,University of Savoy | Audemard F.,Venezuelan Foundation for Seismological Research FUNVISIS | And 4 more authors.
Comptes Rendus - Geoscience | Year: 2016

The Cariaco Basin and the Gulf of Cariaco in Venezuela are two major basins along the seismogenic El Pilar right lateral fault, among which the Cariaco Basin is a pull-apart. Both basins are sites of anoxia and organic-rich deposits. To examine whether the sediments in the Gulf of Cariaco have recorded traces of historical or prehistorical earthquakes, we extracted and analyzed twelve 1 m-long gravity cores, sampling the last millennium sedimentation. We focused on analyzing the sediment sources with different techniques (particle size analysis, XRF, loss on ignition tests, magnetic properties, Rock-Eval pyrolysis, 14C dating). The results confirm that major upwelling occurs at the western gulf entrance and makes deep water flowing from the Cariaco Basin into the Gulf of Cariaco. These flows carry an organic-rich suspended load. Furthermore, we found evidence of a particular, widespread fine-grained siliciclastic deposit (named SiCL3) within the gulf, whose age suggests that it likely formed during the large 1853 AD earthquake that stroke the Cumaná city. We suggest that the earthquake-induced large submarine landslides that modified the topography of the gulf's entrance, which in turn promoted upwelling and open marine water flows from the Cariaco Basin. The layer SiCL3 would be the sediment load remobilized during this chain of events. © 2015 Académie des sciences.

Audemard F.A.,Venezuelan Foundation for Seismological Research FUNVISIS | Audemard F.A.,Central University of Venezuela | Beck C.,University of Savoy | Carrillo E.,Central University of Venezuela
Geomorphology | Year: 2010

Two very large deep-seated gravitational slope deformations in the highlands of the Mérida Andes, Venezuela, are herein described: the Mucubají Pass and Cerro La Camacha. These slope movements have slid in post-Last Glacial Maximum times. In addition, both landslides are in very close association with the active Boconó Fault trace. The Cerro La Camacha (Camacha Range) landslide is fault bounded along its northwest flank, whereas the Mucubají pass mass movement is even cut by the active fault trace. The almost 10 km long Mucubají slide mobilizes LGM moraine deposits along the unconformable basement contact. La Camacha slope movement is a sackung-type landslide, involving two huge masses that affect the entire northwestern slope of the La Camacha Range. This sackung is at least 20 km long, paralleling the active Boconó Fault trace. Combination of high relief energy (gravitational forces) and seismic shaking related to an on-site active fault could be responsible for the destabilization of the slopes or massif in both cases. Although the seismically-induced (re-)activation of the La Camacha landslide is very likely, there is no proof for that yet. Conversely, the Mucubají slide shows geomorphic, geodetic and sedimentary evidence of episodic activity in recent times, which could be ascribed to seismic triggering. In the particular case of the La Camacha sackung, the combination of dextral slip along the Boconó Fault and a SE-dipping fault plane could additionally favor the destabilization of the NW slope of the La Camacha Range. © 2010 Elsevier B.V.

Audemard M. F.A.,Venezuelan Foundation for Seismological Research FUNVISIS | Castilla R.,Total S.A.
Journal of South American Earth Sciences | Year: 2016

This paper presents a compilation of 16 present-day stress tensors along the southern Caribbean plate boundary zone (PBZ), and particularly in western and along northern Venezuela. As a trial, these new stress tensors along PBZ have been calculated from inversion of 125 focal mechanism solutions (FMS) by applying the Angelier & Mechler's dihedral method, which were originally gathered by the first author and published in 2005. These new tensors are compared to those 59 tensors inverted from fault-slip data measured only in Plio-Quaternary sedimentary rocks, compiled in Audemard et al. (2005), which were originally calculated by several researchers through the inversion methods developed by Angelier and Mechler or Etchecopar et al. The two sets of stress tensors, one derived from geological data and the other one from seismological data, compare very well throughout the PBZ in terms of both stress orientation and shape of the stress tensor. This region is characterized by a compressive strike-slip (transpressional senso lato), occasionally compressional, regime from the southern Mérida Andes on the southwest to the gulf of Paria in the east. Significant changes in direction of the maximum horizontal stress (σH = σ1) can be established along it though. The σ1 direction varies progressively from nearly east-west in the southern Andes (SW Venezuela) to between NW-SE and NNW-SSE in northwestern Venezuela; this direction remaining constant across northern Venezuela, from Colombia to Trinidad. In addition, the σV defined by inversion of focal mechanisms or by the shape of the stress ellipsoid derived from the Etchecopar et al.'s method better characterize whether the stress regime is transpressional or compressional, or even very rarely trantensional at local scale. The orientation and space variation of this regional stress field in western Venezuela results from the addition of the two major neighbouring interplate maximum horizontal stress orientations (σH): roughly east-west trending stress across the Nazca-South America type-B subduction along the pacific coast of Colombia and NNW-SSE oriented one across the southern Caribbean PBZ. Meanwhile, northern Venezuela, although dextral strike-slip (SS) is the dominant process, NW-SE to NNW-SSE compression is also taking place, which are both also supported by recent GPS results. © 2016 Elsevier Ltd

Colon S.,CNRS Institute of Earth Sciences | Audemard F.A.,Venezuelan Foundation for Seismological Research FUNVISIS | Beck C.,CNRS Institute of Earth Sciences | Avila J.,Venezuelan Foundation for Seismological Research FUNVISIS | And 5 more authors.
Marine and Petroleum Geology | Year: 2015

A new high resolution shallow marine seismic survey provides further insights on the fault source of the October 29th, 1900 earthquake, which affected a large region of North-central Venezuela, both offshore islands and mainland. This Mw 7.6 to 7.7 seismic event has been indistinctly ascribed to either the La Tortuga or San Sebastián fault, which has installed a live debate among different authors. These two faults allegedly run roughly east-west offshore, along the Coastal range. The San Sebastián fault (SSF) bounds this range to the north, being responsible for its linearity and the steep slope of its northern flank, whereas the La Tortuga fault (LTF) would do about the same, but some 20-30 km farther north, based on acoustic surveys carried out in the late 70's and early 80's. We herein bring strong evidence to support that the SSF is the source fault of this major offshore earthquake, mainly based on the freshness of its submarine scarp and recent fault throw, preserved at the Chuspa bay (close to Cabo Codera, eastern end of the Coastal range in central Venezuela), as depicted by one of the profiles. In addition, it is shown that most of the previous extent ascribed to LTF is not so. The LTF, besides exhibiting mainly normal slip, is much shorter than originally proposed. This precludes that LTF may have the seismic potential for an earthquake as big as the 1900 event. Finally, available reflection seismic data reveal the existence of a major fault system bounding the La Guaira shelf on the north, which exhibits tectonic inversion of pre existing extensional faults, shortening and strong syn-tectonic deformation during the Plio-Quaternary deposition. Sedimentation in the Bonaire basin during the Plio-Quaternary time is strongly controlled by this system activity. © 2015 Elsevier Ltd.

Lorenzoni L.,University of South Florida | Benitez-Nelson C.R.,University of South Carolina | Thunell R.C.,University of South Carolina | Hollander D.,University of South Florida | And 4 more authors.
Marine Geology | Year: 2012

A sediment density flow was observed in the eastern Cariaco Basin during September 2008. Evidence suggests that this flow was likely triggered by a magnitude 5.2 earthquake that occurred on August 11, 2008, with an epicenter located at 10.51°N, 64.17°W (off the city of Cumaná, Venezuela). Elevated suspended sediments near the bottom were observed at the mouth of the Manzanares Canyon (>90gm -2, over a depth of 165m) and decreased to ~11gm -2 (over a depth of 40m) 42km away from the canyon's mouth at the CARIACO Ocean Time-Series site. The sediment flux associated with this single event was ~10% of the total annual sediment flux that typically reaches the Cariaco Basin deep seafloor. Carbon to nitrogen ratios and isotope composition confirm that most of the organic matter transferred by the sediment flow was of continental origin (C/N ratios of ~17.67, δ 13C of -27.04‰, and δ 15N of 6.83‰). Our observations contribute to the growing body of evidence that suggests that submarine canyons are rapid, efficient sediment conduits of particles from shallow to deep waters, and that they should be included in efforts to constrain estimates of sediment and terrestrially derived carbon transport from the continental shelves to the deep ocean. © 2011 Elsevier B.V.

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