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Características sismogénicas de las fallas de Oca-Ancón,Mene Grande y Valera (Región nor-occidental de Venezuela)

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Abstract

Purpose was to characterise seismogenic parameters of Oca-Ancon, Valera and Mene Grande and faults. Estimated velocities: 2.5 - 4 mm/a,1 mm/a and 0.1 mm/a. Max. Probable Magnitudes :7.5, 6.9 and 6.2 Time recurrence: 1000 years,2000 years and 1200 years. Two trenches along active traces of Mene Grande and Valera faults are shown.
... e . : Pantosti , 1997 ) recommend choosing a fault compris - ing several fault planes within the trench because it eases to identify the sequence of seismic events on this active feature , like at Mene Grande ( Soulas and Giraldo , 1994 ) and Morro de Los Hoyos ( Audemard et al . , 1999b ) . ...
... Similarity between both assessments resides on the fact that both faults run along the foot of a prominent fault scarp , up to 18 m high in Cordero , that exerts similar sedimentary controls . Instead , for the Mene Grande fault at the Mene Grande trench , Soulas and Giraldo ( 1994 ) based their earthquake recognition on cases 3 ( colluvial wedge ) and 4 ( sealed upper fault termination or event horizon ) of Fig . 12 . ...
Article
The privileged location of Venezuela along an active interplate deformation belt, despite of being a “so-called” developing country, has led to a long paleoseismic tradition as attested by 45 trench assessments since 1968. Since then, a first 2-trench study was carried out by the American Woodward-Clyde company across the Oca fault at Sinamaica. Since 1980, all further paleoseismic studies have been performed by FUNVISIS and the Uribante-Caparo hydroelectric project (southern Mérida Andes) became their first assessment where 22 huge trenches were bulldozer-dug. Except for these Compañía Anónima de Administración y Fomento Eléctrico (CADAFE) financed trenches and two others, all other assessments were for Petróleos de Venezuela S. A. —PDVSA-.
... In terms of slip rate, most Quaternary tectonic features in Northern Falcón are rather slow, showing slip rates generally below 0.4 mm/a. The major Oca-Ancón fault system is the exception to this, with a maximum slip rate close to 2 mm/a (Audemard 1993, Audemard and Singer 1994, Audemard et al. 1994, Soulas and Giraldo 1994, Audemard 1996, Audemard and Singer 1996, Audemard et al. 2000. The Coast and Interior ranges of northcentral and eastern Venezuela is the only portion of the plate boundary zone to result from rather simple direct interaction between the Caribbean and South America plates. ...
Article
Spatial configuration of Quaternary active tectonic features along the southern Caribbean plate boundary suggests that the region is subject to a compressive strike-slip (transpressional senso lato) regime, characterized by a NNW-SSE maximum horizontal stress (σH=σ1) and/or an ENE-WSW minimum (σh=σ3 or σ2) horizontal stress. Stress inversion applied to fault-plane kinematic indicators measured essentially in Plio-Quaternary sedimentary rocks confirms this tectonic regime. Accordingly, this stress regime is responsible for the Quaternary activity and kinematics of six sets of brittle features along northern Venezuela (from Colombia in the west to Trinidad in the east): (1) east-west rightlateral faults, (2) NW right-lateral faults -acting as synthetic Riedel shears-, (3) ENE to east-west dextral faults -P shears-, (4) NNW normal faults, (5) almost north-south left-lateral faults -antithetic Riedel shears- and (6) mostly subsurface ENE reverse faults associated with folding of the same orientation. Brittle deformation conforms to the simple shear model, although not all the deformation can be accounted for it since strain partitioning is also taking place because regional folding and thrusting are due to the normal-to-structure component of the relative slip vector between the Caribbean and South America plates. On the other hand, the maximum horizontal stress in western Venezuela, particularly in the Maracaibo block and south of the Oca-Ancón fault, progressively turns counter-clockwise to become more east-west oriented, producing left- and right-lateral slip along the north-south striking and NE-SW striking faults, respectively. The orientation and spatial variation of this regional stress field in western Venezuela results from the superposition of the two major neighboring 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 stress across the southern Caribbean boundary zone.
... In terms of slip rate, most Quaternary tectonic features in Northern Falcón are rather slow, showing slip rates generally below 0.4 mm/a. The major Oca-Ancón fault system is the exception to this, with a maximum slip rate close to 2 mm/a (Audemard 1993, Audemard and Singer 1994, Audemard et al. 1994, Soulas and Giraldo 1994, Audemard 1996, Audemard and Singer 1996, Audemard et al. 2000. The Coast and Interior ranges of northcentral and eastern Venezuela is the only portion of the plate boundary zone to result from rather simple direct interaction between the Caribbean and South America plates. ...
Article
Full-text available
Spatial configuration of Quaternary active tectonic features along the southern Caribbean plate boundary suggests that the region is subject to a compressive strike-slip (transpressional senso lato) regime, characterized by a NNW-SSE maximum horizontal stress (σ H=σ1) and/or an ENE-WSW minimum (σh=σ3 or σ2) horizontal stress. Stress inversion applied to fault-plane kinematic indicators measured essentially in Plio-Quaternary sedimentary rocks confirms this tectonic regime. Accordingly, this stress regime is responsible for the Quaternary activity and kinematics of six sets of brittle features along northern Venezuela (from Colombia in the west to Trinidad in the east): (1) east-west right-lateral faults, (2) NW tight-lateral faults-acting as synthetic Riedel shears-, (3) ENE to east-west dextral faults -P shears-, (4) NNW normal faults, (5) almost north-south left-lateral faults -antithetic Riedel shears- and (6) mostly subsurface ENE reverse faults associated with folding of the same orientation. Brittle deformation conforms to the simple shear model, although not all the deformation can be accounted for it since strain partitioning is also taking place because regional folding and thrusting are due to the normal-to-structure component of the relative slip vector between the Caribbean and South America plates. On the other hand, the maximum horizontal stress in western Venezuela, particularly in the Maracaibo block and south of the Oca-Ancón fault, progressively turns counter-clockwise to become more east-west oriented, producing left- and right-lateral slip along the north-south striking and NE-SW striking faults, respectively. The orientation and spatial variation of this regional stress field in western Venezuela results from the superposition of the two major neighboring 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 stress across the southern Caribbean boundary zone.
Article
Full-text available
Venezuela forms part of an important hydrocarbon province, defined by the presence of prolific Cretaceous source rocks, which extends across northern South America. By early 1997, the country had produced 53 billion barrels of oil. Reserves are estimated to total 73 billion barrels of oil and 146 TCF of gas with 250 billion barrels recoverable in the Heavy Oil Belt. Most reserves are located within the intermontane Maracaibo and foreland Barinas-Apure and Eastern Venezuela Basinx They correspond to more than 1.5 trillion BOE originally in place.
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