480 Revista de la Asociación Geológica Argentina 61 (4): 480-491 (2006)

QUATERNARY FAULTS AND STRESS REGIME OF VENEZUELA

Franck. A. AUDEMARD M1, André SINGER P., Jean-Pierre SOULAS and the Neotectonics Section of the Funvisis Earth Sciences Department*

¹ Funvisis, Apartado Postal 76.880, Caracas 1070-A, Venezuela. E-mail: [email protected].

ABSTRACT Spatial configuration of Quaternary active tectonic features along the southern Caribbean plate boundary suggests that the region is subject σ σ to a compressive strike-slip (transpressional senso lato) regime, characterized by a NNW-SSE maximum horizontal stress ( H= 1) and/or an σ σ σ ENE-WSW minimum ( h= 3 or 2) 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 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 rela- tive 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 orien- ted, 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 σ horizontal stress orientations ( H): 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.

Keywords: Quaternary tectonics, fault-slip data, stress tensor, Caribbean, Venezuela.

RESUMEN: Fallas y campo de esfuerzos cuaternarios de Venezuela. La configuración espacial de los rasgos tectónicos activos cuaternarios en el Caribe meridional sugiere que esta región está sujeta a un régimen tec- σ σ tónico transcurrente compresivo (transpresivo senso lato), caracterizado por un esfuerzo horizontal máximo ( H= 1) de dirección NNO-SSE y un σ σ σ mínimo ( h= 3 or 2) orientado ENE-OSO. La aplicación de métodos de inversión a datos microtectónicos determinados sobre planos de fallas afectando rocas sedimentarias esencialmente de edad plio-cuaternarias confirma este régimen tectónico. Consecuentemente, este régimen es res- ponsable por la cinemática y actividad cuaternaria de seis familias de estructuras tectónicas frágiles a lo largo del norte de Venezuela (desde Colombia en el oeste hasta Trinidad en el este): (1) fallas dextrales este-oeste, (2) fallas dextrales NO que actúan como "Riedels" sintéticos-, (3) fallas dextrales ENE a este que se comportan como fracturas P, (4) fallas normales NNO, (5) fallas sinestrales submeridianas consideradas como fractu- ras "Riedels" antitéticos y (6) fallas inversas ENE - sub-paralelas al plegamiento de la misma orientación. En esta región en particular, la deforma- ción frágil obedece el modelo de cizalla simple, aunque no toda la deformación puede atribuírsele porque simultáneamente ocurre partición de la deformación porque el plegamiento y fallamiento inverso se debe esencialmente a la componente ortogonal a las estructuras del vector de despla- zamiento relativo entre las placas Caribe y Suramérica. Por otra parte, el esfuerzo máximo horizontal en Venezuela occidental, particularmente en el bloque de Maracaibo y al sur de la falla de Oca-Ancón, progresivamente tuerce en sentido anti-horario para orientarse este-oeste, permitiendo la activación simultánea de fallas sinestrales y dextrales de orientación norte y NE respectivamente. La orientación y variación espacial del campo de esfuerzo regional en Venezuela occidental resulta de la superposición de las orientaciones de los dos esfuerzos horizontales máximos imperan- σ tes en el norte de Suramérica ( H): el esfuerzo de orientación este-oeste producto de la subducción de la placa Nazca por debajo de la costa pací- fica de Colombia y el esfuerzo orientado NNO-SSE a través del límite de placas del Caribe meridional.

Palabras clave: Tectónica cuaternaria, microtectónica, tensores de esfuerzos, Caribe, Venezuela.

INTRODUCTION generated in the frame of an ILP II-2 pro- Vladimir Trifonov of Russia, responsible ject, "Major Active Faults of the World", for the Eastern Hemiphere. The South This paper presents an updated compila- led by Michael Machette of the USGS, res- Americam maps and data compilation tion of the Quaternary faults of Venezuela, ponsible for the Western Hemisphere, and efforts were coordinated by Carlos Costa of

* The following professionals have once belonged to (or worked for) the FUNVISIS Neotectonics section: Luis Acosta, Amalfi Arzola, Carlos Beltrán, Christian Beck, Olivier Bellier, Didier Bonnot, Jean-Claude Bousquet, Eduardo Carrillo, Antonio Casas-Sainz, Raymi Castilla, Carlos Costa, Feliciano De Santis, Hans Diederix, Claudio Gallardo, Carlos Giraldo, Rogelio González, Antoine Mocquet, Reinaldo Ollarves, Carlos Alberto Rivero, Eduardo Rodríguez, José Antonio Rodríguez, Carlos Rojas, Bernard Sauret, Carlos Schubert and Tomas Subieta.

0004-4822/02 $00.00 + $00.50 C 2006 Revista de la Asociación Geológica Argentina Quaternary faults and stress regime of Venezuela 481

Figure 1: Simplified general geodynamic setting of the southern Caribbean (modified from Audemard, 2002). Region is subject to a complex block tectonics. Vector decomposition of the convergence vector at the Nazca subduction may explain the along-strike slip change of the Romeral fault system. Equivalence of used acronyms is as follows: Bonaire (BB), Chocó (CB), Maracaibo (MTB), North Andean (NAB) and Panamá (PB) blocks; Mérida Andes (MA) and Pamplona indenter (PI). Some major faults are also reported: Algeciras (AF), Boconó (BF), El Pilar (EPF), Guaicaramo (GF), Romeral (RFS), Santa Marta-Bucaramanga (SMBF), San Sebastián (SSF) and Oca-Ancón (OAF); and other features as well: Leeward Antilles subduction (LAS), Los Roques Canyon (LRC), North Panamá deformation belt (NPDB), and Southern Caribbean deformation belt (SCDB).

the University of San Luis in Argentina. America (Bell 1972, Malfait and Dinkelman in a direction 086º ± 2º with respect to the The Quaternary fault map data of Vene- 1972, Jordan 1975, Pindell and Dewey Central range of Trinidad predicted by zuela, updated until 1998, are compared to 1982, Sykes et al. 1982, Wadge and Burke Weber et al. (2001), and N084º ± 2ºE with stress tensors derived from fault-plane kine- 1983, among others). Lately, this has been respect to South America (Canoa site) by matic indicators measured essentially in strongly supported by results of recent Pérez et al. (2001) from GPS data, which sedimentary rocks of Plio-Quaternary age GPS surveys (Freymueller et al. 1993, suggest almost pure wrenching with only and compiled by Audemard et al. (2005). In Kaniuth et al. 1999, Weber et al. 2001, Pérez slight transtension in eastern Venezuela, an this paper these will be discussed in terms et al. 2001, Trenkamp et al. 2002). Never- issue which shall be discussed in more of their significance with respect to the theless, this Caribbean-South America pla- detail later in this paper. This wide trans- interactions among the Caribbean, South te boundary -which drives and defines acti- pressional boundary (in its widest defini- America and Nazca plates and the smaller ve tectonics along northern Venezuela tion, signifying coexistence of strike-slip continental blocks of northwestern South (from Colombia to Trinidad)- can not be and compression but not necessarily acco- America. classified solely as being of the simple dex- mmodated jointly on one single structure) tral type (Soulas 1986, Beltrán 1994) since it extends southwestward into the Mérida GENERAL GEODYNAMIC comprises a more than 100 km wide active Andes (MA in Fig. 1). The plate boundary SETTING transpressional zone occurring partly offs- in western Venezuela covers a 600 km wide hore and partly onshore northern Ve- zone and comprises a set of discrete tecto- Western Venezuela and northern Colombia nezuela (Audemard 1993, Singer and Aude- nic blocks or microplates (Fig. 1), which are situated in a very complex geodynamic mard 1997, Audemard 1998, Ysaccis et al. move independently among the surroun- setting involving a number of tectonic 2000). Important positive relief features ding larger plates (Caribbean, South Ame- blocks or microplates. Conversely, northern within the onshore portion of this plate rica and Nazca). The Maracaibo block Venezuela essentially lies in the direct inter- boundary zone, such as the Coastal and In- (MTB in Fig. 1) which stands out among action zone between the South America terior ranges (I, J and Q in Fig. 2), line the those blocks for its perfect triangular shape, and Caribbean plates (Fig. 1) and there is a entire northern and part of the eastern Ve- is bounded by the left-lateral strike-slip general consensus on the eastward motion nezuelan coast. This would seem inconsis- Santa Marta-Bucaramanga fault (SMBF) in of the Caribbean plate relative to South tent with the Caribbean plate motion vector Colombia and the right-lateral strike-slip 482 F. A. AUDEMARD M, A. SINGER P., J.P. SOULAS AND OTHERS

Figure 2: Schematic map of Quaternary faults of Venezuela (simplified from Audemard et al. 2000). Faults and toponyms used throughout this contribution are identified. Very few localities are only reported in figure 4.

Boconó fault (BF) in Venezuela and separa- geodynamic configuration results from a thern portion of the plate boundary ted in the north from the Bonaire block transpressive evolution that has occurred (Audemard 2000) and clearly indicates that, (BB in Fig. 1) by the right-lateral strike-slip throughout the Tertiary and Quaternary, through time, the plate boundary zone has Oca-Ancón fault (OAF). Besides, both the initiated as an oblique type-B subduction. progressively changed from a predominant Maracaibo and Bonaire blocks are being The NW-dipping oceanic lithosphere, atta- compressive to a more wrenching type. extruded northward with the Bonaire block ched to northern South America, subduc- This change started at around 17-15 Ma in moving slightly east. Together they are over- ted obliquely under Caribbean plate island northwestern Venezuela (Audemard 1993, riding the Caribbean plate north of the arc. This plate boundary zone later evolved 1998). The tectonically complex southeas- Leeward Antilles islands, where a young into a long-lasting east-younging oblique- tern Caribbean is undergoing two major south-dipping, amagmatic, flat subduction collision, where Caribbean-affinity nappes geodynamic processes: (a) strain partitio- (LAS) has developed in recent times (main- overrode towards the SSE, thus scrapping ning characterized by NNW- trending shor- ly during the last 5 ma). The tectonic extru- off passive-margin-affinity nappes and tening across the entire region from north sion of these blocks is induced by the colli- incorporating them into the tectonic pile, of La Blanquilla island (O in Fig. 2) to the sion of the Panamá arc (PB in Fig. 1) which in turn was all overthrusted onto the southernmost active thrust front of the against the Pacific side of northern South undeformed South America passive mar- Interior range and right-lateral strike-slip America and its subsequent suturing gin. More recently, this plate boundary con- along the main east-west striking El Pilar (Audemard 1993, 1998). Recent results verted into a partitioned transpression and NW-SE striking Los Bajos-El Soldado from GPS plate motion studies (Freymue- when and where collision became unsustai- faults, as well as along other minor parallel ller et al. 1993, Kellogg and Vega 1995, nable (for more details refer to Audemard and/or synthetic Riedel shear faults (Fig. 2); Kaniuth et al. 1999, Trenkamp et al. 2002), 1993, 1998). Its latest evolutionary stage is and (b) slab detachment associated with an such as the CASA project, confirm this still active in Eastern Venezuela and incipient type-A subduction (e.g., Russo northeastward escape of both blocks, Trinidad and marks the shift from oblique and Speed 1992, Russo 1999; responsible which in the process generate the Southern subduction to present-day partitioned obli- for the largest onshore negative Bouguer Caribbean Deformation Belt (SCDB) north que collision. This east-younging oblique anomaly of the world, located south of the of the Netherlands Leeward Antilles. convergent margin has acted diachronically southern edge of the Interior range). These The present Caribbean-South American throughout the evolution of this entire nor- processes concur with a plate boundary Quaternary faults and stress regime of Venezuela 483

geometry such as the present one, where A large portion of the dextral slip along this pect to South America is moving at rates the El Pilar fault transfers its slip eastward complex boundary seems to be presently between 12 mm/a in the west (geologic slip to one of its synthetic Riedel shears (Los accommodated by the major right-lateral rate from Nuvel 1-A model) and 18 ± 2 Bajos and El Soldado faults), which is ac- strike-slip Boconó-San Sebastián-El Pilar- mm/a in the east (GPS-derived slip rate by ting as a "lithospheric tear fault", thus se- Los Bajos fault system or segments of it Weber et al. 2001), the present major strike- parating the transpressional boundary on (Molnar and Sykes 1969, Minster and slip (Boconó-San Sebastián-El Pilar-Warm the west from the conventional type-B Jordan 1978, Pérez and Aggarwal 1981, Spring faults) boundary slips at ~ 1 cm/a Lesser Antilles subduction zone on the east. Schubert 1980a and b, 1982, Stephan 1982, (Pérez and Aggarwal, 1981; Soulas, 1986; These two distinct seismotectonic domains Aggarwal 1983, Schubert 1984, Soulas Freymueller et al., 1993; Audemard et al., were originally identified by Pérez and 1986, Beltrán and Giraldo 1989, Singer and 2000; Pérez et al., 2001, Weber et al. 2001, Aggarwal (1981). The different seismicity Audemard 1997, Audemard et al. 2000, Trenkamp et al. 2002). Secondary faults patterns support contrasting geodynamic Weber et al. 2001, Pérez et al. 2001). This however have slip rates one order of mag- contexts (oblique collision and oblique sub- slip is now known to be transferred farther nitude less and in fact most of them exhibit duction roughly west and east of the Los east onto the Warm Springs fault system of slip rates under 0.5 mm/a, with the excep- Bajos-El Soldado fault system, respective- central Trinidad (after Weber et al. 2001's tion of the Oca-Ancón (2 mm/a, estimated ly). Recent GPS findings by Weber et al. results). It is still matter of debate whether from a paleoseismic assessment performed (2001) indicate that most of the strike-slip this is either a transcurrent or transform by Audemard, 1996), the Burbusay ( <3 motion of the El Pilar fault is transferred system and depends on the authors and mm/a), Valera and La Victoria ( <1 mm/a) onto the Warm Springs fault system of the their proposed geodynamic models. Most faults (for more details, refer to Audemard Central Range of Trinidad rather than onto authors accept or postulate this major right- et al. 2000, and to figure 2 for relative loca- a fault south off Trinidad (Fig. 2). This lateral strike-slip fault system to be the plate tion). would imply that the Paria gulf is functio- boundary between the Caribbean and ning at present as a pull-apart basin boun- South America plates (e.g., Hess and NEOTECTONIC MAPPING IN ded by the El Pilar and Warm Springs faults Maxwell 1953, Schubert 1979, Aggarwal VENEZUELA on the north and south respectively, at a 1983, among many others), whereas few releasing stepover. Both faults exhibit a others propose different plate boundary Active tectonics in Venezuela at present are similar slip rate, in the order of 8-10 mm/a models along this right-lateral strike-slip driven by tectonic plate and microplate in- (compare Audemard et al . 2000 and Saleh et plate boundary zone: (a) orogenic float type teractions, as explained in the introduction. al. under review). However, this crustal for the Andes (Audemard, 1991, Jácome, Knowledge about the southern Caribbean deformation does not exclude that a major 1994, Audemard and Audemard 2002, Fig. plate boundary zone has much evolved from plate boundary is underlying this region, as 3) or eastern Venezuelan Coastal and In- the original ideas of Hess and Maxwell evidenced by the instrumental seismicity, a terior ranges (Ysaccis et al. 2000), thus being (1953), when a rather simple dextral wren- conclusion originally drawn by Pérez and flanked by both an A- and B-type subduc- ching system had been proposed. Over Aggarwal (1981) and later confirmed by tions; and (b) SE-directed A-subduction or twenty years of neotectonic analysis com- Sobiesiak et al. (2002). underthrusting of the Maracaibo block prising studies in the disciplines of surface As in eastern Venezuela, strain partitioning under the Mérida Andes (Kellogg and geology, geomorphology, microtectonics, is also a common feature along the rest of Bonini 1982, De Toni and Kellogg 1993, seismotectonics and paleoseismology, com- the transpressional boundary zone. In the Colletta et al. 1996, 1997). However, the bined with data from conventional geologic Mérida Andes, strain is nicely partitioned incorporation of the Boconó fault into this studies and seismic reflection surveying between the right-lateral strike-slip Boconó major right-lateral strike-slip fault system is both onshore and offshore, now give us a fault (BF) running slightly oblique along the a rather recent event, that relates to the more complete understanding of the com- axis of the chain and thrust faults bounding northward extrusion of the Maracaibo plex active geologic setting in Venezuela the chain on both flanks (Audemard and block, because the former transcurrent and surrounding areas. Audemard 2002). The north-central coastal boundary used to comprise the east-west- Neotectonics in Venezuela, as for every- ranges also exhibit strain partitioning, striking Oca-Ancón fault system (OAF) where else in the world, is defined as the where dextral slip in the range core is located farther north in northwestern tectonics resulting from the most recent accommodated by both the San Sebastián Venezuela (Audemard 1993, 1998). The- and still active stress field. On this basis, and La Victoria faults and other minor refore, the Oca-Ancón fault system belon- Venezuelan neotectonics refer to the tecto- synthetic Riedel shears whereas transverse ged to this major right-lateral strike-slip nics of the Quaternary (after Soulas 1986), shortening is mainly taken by uplift and the plate boundary zone along the southern implying that tectonic features that either frontal thrust faults bounding the chain Caribbean from when transpression started show no evidence of activity during that along its southern edge, such as in the Gua- at around 17-15 Ma to when essentially cea- timeframe or have an orientation not sus- rumen basin (Cojedes state; Audemard sed or considerably slowed down at around ceptible to reactivation in the near future 1999a). 5-3 Ma. Although the Caribbean with res- under the present stress regime, are not in- 484 F. A. AUDEMARD M, A. SINGER P., J.P. SOULAS AND OTHERS

Figure 3: The orogenic float model applied to the Mérida Andes. Cross-section extends from the northwestern tip of the Santa Marta Block (SMB; location in Fig. 2) to the Llanos Basin, across the southernmost Mérida Andes, at the Pamplona indenter. Bottom figure displays major geologic units and structures, whereas top figure only exhibits major structures -brittle thrust and strike-slip faults, detachments and triangle zones- to give a more legible view of their interplays (after Audemard and Audemard 2002).

cluded in this compilation. The latest ver- of latest activity and slip rate, which allows The Quaternary deformation does not sion of the neotectonic (Quaternary fault) easy and quick identification of the major occur all over the country. Instead, strain is map depicted in figure 4 is the third version active features. The map is complemented concentrated along localized strips or belts of this type of maps (Audemard et al. with a database that contains relevant infor- (Singer and Audemard 1997); all of them 2000), the first version having been elabora- mation about each fault and/or fault sec- located in western and northern Venezuela. ted by Soulas in 1985, and published in tion (length, attitude, age, sense of slip, slip Most of these mobile belts exhibit high 1986 (Soulas 1986), which was later upda- rate, geomorphic expression, latest activity positive relief, implying an important ted by Beltrán (1993) as the second version. from geologic data, and so on) and its seis- amount of shortening along the plate The latest version differs from the previous mogenic potential (maximum credible boundary. It does not exclude however that ones in three important aspects: (a)- New earthquake and its recurrence). For more some belts show negative relief but such neotectonic data corresponding to onshore details, the reader is referred to the USGS features are always of more local extent. areas studied by Funvisis between 1993 and web page. The most conspicuous mobile belt is at 1999 have been incorporated. They include least 100 km wide and runs over 1200 km in data on the southern frontal thrusts of the QUATERNARY TECTONICS OF VE- length from the Colombian border near San Interior range in eastern Venezuela and the NEZUELA Cristobal in the southwest into Trinidad in southern foothills of the Mérida Andes, as the east. This major belt -which seems to be well as a preliminary assessment of the As mentioned earlier, most of northern and the prolongation of the Eastern Cordillera inner active deformation of the triangular western Venezuela is situated in a complex of Colombia- corresponds to an alignment block defined by the Oca-Ancón, Boconó plate boundary zone. Due to this comple- of mountain chains that comprises from and Valera faults; (b)- A reinterpretation of xity, we shall discuss in this paper only the southwest to east: the NE -trending Mérida the San Sebastián-El Pilar relay at the most relevant aspects of the Quaternary Andes and the E-W-oriented Coast and Cariaco trough in accordance with the in- Venezuelan tectonics. Figure 2 portrays all Interior ranges both in north-central and terpretation of Blanco and Giraldo (1992); names of the active tectonic features used northeastern Venezuela. This belt exhibits a and (c) The map has been simplified in throughout this paper, while figure 4 first-order dextral fault system that mostly terms of the number of faults (imposed by (Audemard et al. 2000) represents the ver- runs along the chain's backbone over a dis- the aim of the ILP-II-2 project), particu- sion of the map of the ILP project and tance of more than 1200 km and comprises larly in the Colombia-Venezuela border gives further details on the Quaternary acti- the NE-trending Boconó fault in the An- area, known as the Pamplona indenter -PI-. vity and relevance of only the major Qua- des section (VE-06 in Fig. 4), and both the On the other hand, faults exhibit more ternary features of Venezuela. In the follo- E-W-striking San Sebastián fault (VE-16 in detail both with respect to their Quaternary wing, we shall present the main issues Fig. 4) in central Venezuela and the El Pilar kinematics as to their discrimination by age drawn from these two figures. fault (VE-13 in Fig. 4) in eastern Venezuela Quaternary faults and stress regime of Venezuela 485

Figure 4: Map of Quaternary faults of Venezuela (after Audemard et al. 2000). Also accessible as a pdf file from the USGS web page in open file reports (ofr-00-0018). Line thickness is proportional to fault slip rate: the thickest indicates > 5 mm/a and the thinnest < 1mm/a. Shown faults have proven Quaternary activity. (Singer and Audemard 1997). Most of the east in eastern Falcón, along the submarine conó fault bends into the Pamplona inden- dextral slip between the Caribbean and canyon of Los Roques and in the gulf of ter (as defined by Boinet 1985). Here, the South America plates is accommodated by Paria. The three latter ones constitute the Boconó fault sharply changes orientation to this fault system. In fact, this fault system principal areas of negative relief due to the connect with the N-S-striking Chitagá fault, moves at about 1 cm/a when most other significant normal component involved. which shows a strong reverse slip when joi- faults slip slower than a 1 mm/a Another deformation belt is the NNE-tren- ning the Boconó fault, but progressively (Audemard et al. 2000, Pérez et al. 2001). ding Perijá range in westernmost Venezue- becomes a dominant left-lateral fault to- The combination of this rather fast slip rate la, whose crestline defines the borderline wards the south. Farther south, slip is trans- and the significant length of the Boconó- with Colombia. ferred to the NW-trending sinistral Pam- San Sebastián-El Pilar fault system transla- The major Boconó-San Sebastián-El Pilar plona-Chucarima-Morro Negro fault sys- tes into an associated seismicity of modera- fault system displays several structural com- tem (CO-37 in Fig. 4). On the other extre- te frequency and magnitude and is conside- plexities of kilometric to several-kilometre me in the east, in the Paria gulf and red to be responsible for most large (Ms > scale, either in transtension (pull-apart Trinidad, the major right-lateral strike-slip 7) historical earthquakes that have struck basins such as those of La González/San fault system also bends rather sharply, 45º the country since the first ever reported Juan de Lagunillas -south of Mérida-, clockwise this time. The fault system splays event in 1530. Fault rupture is concentrated Cabudare, Cariaco trough and the gulf of into several NW-striking offshore faults - in some particular segments of this plate Paria among others; refer to Fig. 2 for rela- among which are the Los Bajos (VE-15 in boundary (e.g., Rod 1956, Cluff and tive location), or in transpression (Caigüire Fig. 4), El Soldado and Bohordal faults (in Hansen 1969, Aggarwal 1983, Audemard hills at Cumaná, and Las Manoas and Fig. 2)- that exhibit both normal and dextral 1997a, Pérez et al. 1997, Audemard 1999b, Guarapiche -west and east of the 1997 epi- components. Los Bajos-El Soldado fault Audemard 2002). Some secondary mobile centre, respectively, in Fig. 4-; all in Sucre system is claimed to link the major transcu- zones branch off from the major one. The state, in eastern Venezuela and related to rrent fault system to the southern tip of the most important of these are: the E-W-stri- the El Pilar fault). In fact, this major wren- type-B Lesser Antilles subduction; hypothe- king dextral Oca-Ancón fault system (VE- ching fault system has no major complica- sis that is not necessarily shared by Weber et 01 in Fig. 2) in northwestern Venezuela and tion of regional scale, except for both ends al. (2001), who postulate that slip transfer three NW trending normal-dextral fault (Singer and Audemard 1997). In the west, at takes place along the Warm Springs fault of systems respectively located from west to the Colombia-Venezuela border, the Bo- the Central Range of Trinidad from repea- 486 F. A. AUDEMARD M, A. SINGER P., J.P. SOULAS AND OTHERS

ted GPS measurements. At this eastern tip, faults to the main right-lateral strike-slip of compression are chain uplift and build- the El Pilar fault also shows a splay in the fault system. For instance, the San Simón up, and intense folding in sedimentary north compartment that branches off to- and Caparo faults in the Andes run parallel sequences like in the Falcón basin ("D" in wards ENE. This splay, named the Tuna- to the Boconó fault. In north-central Fig. 2), the eastern Interior range ("Q" in puy fault, exhibits a dominant reverse com- Venezuela, the La Victoria fault acts as a P Fig. 2), the Andes foothills, and even in the ponent with minor dextral slip. Beltrán shear with respect to the San Sebastián Neogene-Quaternary foreland sequence of (1998) proposes that the reverse Tunapuy fault. The North Coast in eastern Vene- the central Interior range. fault in the Paria peninsula prolongs into zuela is also dextral and runs north of and Normal faults are also common and wides- the reverse Arima fault of northern Tri- parallel to the el Pilar fault. pread within the deformation belts. Tuña- nidad that bounds the southern foothills of In the north-central and eastern mobile me in the Mérida Andes (VE-05 in Fig. 4), the Northern range of Trinidad (Fig. 2). belts, few faults exhibit left-lateral strike- Los Médanos (north of Coro), Cabo San Weber et al. (2001b) have demonstrated that slip. The Quebrada Chacaito fault trends Román and Puerto Escondido (north tip of the Arima fault, based on calcite and quartz almost north-south, north of Caracas, but the Paraguaná peninsula in northwestern geothermometry applied to south-dipping other slightly oblique faults to the main Venezuela) and the Río San Juan graben (in shear bands and cataclastic zones studied dextral system in northeastern Venezuela eastern Venezuela) faults are some exam- along the southern border of the Northern also exhibit sinistral motion. A case in point ples of normal faulting (refer to Fig. 2 for range in Trinidad, is a south-dipping range- constitutes the Punta Charagato fault in the location). Except for the Tuñame fault loca- bounding normal fault, whose activity as Cubagua island, and the Laguna Grande ted in the Andes (Figs. 2 and 4), all other such could only be constrained between 12 fault in the Araya peninsula (Giraldo and normal faults in northern Venezuela strike and 1 Ma. However, the results of studies Beltrán 1989). The orientation and slip of NNW. Instead, the normal slip of the Tu- by Saleh et al. (under review), based on geo- these left-lateral strike-slip faults seem aty- ñame fault -that roughly strikes ENE and is detic data (triangulation and GPS data mer- pical with respect to their tectonic setting in located at the convergence of the Valera ging), argue for a reverse slip along the northeastern Venezuela. These ENE-stri- and Boconó faults- is a consequence of a Arima fault. This would seem to confirm king faults, in combination with the east- void effect induced by a bookshelf rotation the Arima fault slip determined from aerial- west striking dextral faults, bound wedge- mechanism produced by simple shear bet- photo interpretation based on landforms of shaped tectonic blocks, whose acute angle ween the Oca-Ancón and Boconó faults. Quaternary activity performed by Beltrán points to between ENE and east. Some Dhont et al. (2005) propose instead that the (1998). blocks in this region show a slip vector that axial extension within the central Andes, Several second-order faults of considerable slightly diverges to ENE (N084º ± 2ºE involving the Tuñame fault, responds to the length diverge obliquely from the major after Pérez et al. 2001), which matches northward escape of the Trujillo block, right-lateral strike-slip fault system. Many of rather well with the orientation of the bounded between the north-south-striking these are considered to function simply as bisecting line between both fault trends. left-lateral Valera fault on the west and the large synthetic Riedel shears related to the This could argue for the occurrence of NE-SW-trending right-lateral Boconó fault principal deformation zone marking the block extrusions to some extent in this on the east (Figs. 2 and 4). direct Caribbean-South America plate inter- complex southeastern corner of the Cari- In western Venezuela, the mobile belt is action in north-central and northeastern bbean in order to reduce mass excess. This much wider than in northern Venezuela, Venezuela. The best known faults of this would give a satisfactory explanation to the reaching up to 600 km in width, and com- type are: the Río Guárico (VE-09 in Fig. 4), apparent transtension postulated by other prising the entire Maracaibo block (MTB) Tacagua-El Avila (VE-10 in Fig. 4), Tácata authors from GPS vectors (e.g., Weber et al. that covers also part of northern Colombia (VE-11 in Fig. 4), Píritu (VE-12 in Fig. 4), 2001), when transpression is actually the (Audemard, 2000; Audemard et al., 2000). San Mateo (Jose; VE-14 in Fig. 4), Urica operating mechanism at plate-boundary This block is bounded by the sinistral and San Francisco faults, among several scale. Bucaramanga fault (SMBF in Fig. 1) on the others. In the Mérida Andes, along the Active thrust faults are present along most southwest and the dextral Boconó and Boconó fault, there is no manifestation of chain fronts, although they may be blind or Oca-Ancón faults. Other authors consider such large Riedel shears, although there are hidden behind triangular zones or intracu- the northern boundary of the block to be many branching faults. Among them deser- taneous wedges. They have been detected the flat subduction (LAS in Fig. 1), respon- ve mention the north-south-striking sinis- onshore along the northern edge of the sible for the Southern Caribbean Defor- tral Valera (VE-04 in Fig. 4) and Burbusay presently inverted Falcón basin (south of mation Belt (SCDB) established from seis- faults and the subparallel dextral Caparo Coro), along the foothills on both flanks of mic tomographic studies by Van der Hilst fault (SE of San Cristobal; Fig. 2). The pre- the Mérida Andes and along the southern (1990), rather than the Oca-Ancón fault sence of R shears, in this case in association front of the Interior range both in central system (OAF in Fig. 1). In Venezuelan terri- with the Oca-Ancón fault system, also hap- (e.g., Cantagallo overthrust) and eastern tory, this block contains two deformation pens in the Falcón range. Dextral slip is also (e.g., Pirital and sub-parallel thrusts) Vene- belts with positive relief: the Perijá range accommodated by sub-parallel-trending zuela (Figs. 2 and 4). Other manifestations and the western part of the Mérida Andes, Quaternary faults and stress regime of Venezuela 487

between which the Maracaibo basin is being right-lateral faults, as synthetic Riedel shears among which the Cantagallo overthrust); squeezed and shortened in NW-SE direc- to the east-west faults (Urumaco -VE-02-, and (6) ENE to E dextral faults -P shears- tion. The Perijá range happens to be the Río Seco -VE-03-, and La Soledad faults); (La Victoria fault -VE-08-). This is actually least studied area until the present-day in (3) NNW normal faults (Western Para- the only case of active P faulting recogni- terms of active tectonics because of poor guaná, Cabo San Román, Puerto Escon- zed in the plate boundary zone. accessibility and personal security pro- dido and Los Médanos faults, all fault- For eastern Venezuela, the configuration of blems. bounding the Paraguaná peninsula); (4) the active structures is as follows (Figs. 2 The triangular Maracaibo block (MTB) shows North to NNE left-lateral faults, antithetic and 4): (1) East-West right-lateral faults (El an intense internal fragmentation where to the east-west faults (Carrizal, El Hatillo Pilar -VE-13-, El Yaque and North Coast blocks are individualized by north-south to and other minor faults); and (5) ENE rever- faults); (2) NW right-lateral faults, synthetic NE-SW trending faults. Most of these se faults, parallel to fold axis of similar to the main east-west faults (San Mateo - faults are essentially left-lateral in slip, with orientation (Araurima, Taima-Taima/Chu- VE-14-, Urica and San Francisco faults); (3) a minor thrust component in many cases, chure and Matapalo faults). In terms of slip NW to NNW normal-dextral to dextral- such as from west to east: Icotea, Pueblo rate, most Quaternary tectonic features in normal faults (San Juan Graben, Bohordal, Viejo, Valera, Burbusay, among others. This Northern Falcón are rather slow, showing Los Bajos and El Soldado -VE-15- faults); structural and geometrical configuration slip rates generally below 0.4 mm/a. The (4) ENE left-lateral faults, which do not may result from a bookshelf rotation me- major Oca-Ancón fault system is the excep- obey the simple shear model (Laguna chanism induced by simple shear generated tion to this, with a maximum slip rate close Grande and Punta Charagato faults; issue between the dextral Boconó and Oca- to 2 mm/a (Audemard 1993, Audemard discussed earlier in this paper); and (5) Ancón faults (Audemard et al. 1999, 2005). and Singer 1994, Audemard et al. 1994, ENE reverse faults, parallel to fold axis But the two faults are not parallel and are at Soulas and Giraldo 1994, Audemard 1996, orientation (frontal thrust of the Interior an angle of 45º, which is an atypical confi- Audemard and Singer 1996, Audemard et al. range, among which the Pirital thrust guration that must result in particular com- 2000). stands out). plex deformations, as well as switching the The Coast and Interior ranges of north- All present deformations along northern sense of slip along faults through time. central and eastern Venezuela is the only Venezuela are related to the WNW oriented The spatial configuration of the faults and portion of the plate boundary zone to oblique convergence vector of the Cari- folds at regional scale and their kinematics, result from rather simple direct interaction bbean plate with respect to South America as deduced solely from the neotectonic between the Caribbean and South America (e.g.: N 75º W, after Minster and Jordan mapping, points out that the Northern plates. The same applies to northwestern 1978; later confirmed by many others from Falcón basin (northwestern Venezuela) is Venezuela as registered in the Falcón basin GPS data, as indicated earlier). Meanwhile, undergoing a stress tensor with a NNW- and applicable at larger scale to the Bonaire western Venezuela presents a more com- SSE to N-S maximum horizontal stress and block confined between the Leeward An- plex scenario that shall be discussed later in an ENE-WSW minimum (or intermediate) tilles subduction and the Oca-Ancón fault this paper that reflects the influence of the horizontal stress (Audemard 1993, 1997b, system. Therefore, this region also complies convergence vector between the Nazca and 2001; Audemard et al. 2005). This would with the simple shear model, at least as far South America plates to the southwest in mean that the simple shear model associa- as the brittle tectonics is concerned, with Colombian territory. ted with strike-slip faulting proposed by strain partitioning also occurring along this Wilcox et al. (1973) applies. Regional folding plate boundary segment. Within the Me- QUATERNARY STRESS TENSORS in this region does not only result from sozoic metamorphic SSE-overthrusted na- OF VENEZUELA wrenching, as proposed by many authors ppes of central Venezuela, six families of (e.g.: Stephan 1982), but also from regional active tectonic features are distinguishable compression. Both folding due to wren- on the basis of their orientation and pre- Audemard et al. (2005) have recently publis- ching in close association with the Oca- sent kinematics (Figs. 2 and 4): (1) East- hed a nationwide stress tensor compilation Ancón fault system (transpression s.s.) and West right-lateral faults (San Sebastián, La derived from fault-plane kinematic indica- to regional compression occur together Tortuga and El Avila faults); (2) NW right- tors. In order to ascertain the characteriza- (transpression s.l.). The neotectonic map- lateral faults, synthetic to the east-west tion of the latest and still active tectonic ping in this region also permits the determi- faults (Río Guárico -VE-09-, Tácata -VE- phase, this compilation has only integrated nation of active brittle structures in five dis- 11- and Aragüita faults; (3) NW to NNW stress tensors derived from Plio-Quaternary tinguishable families based on their orienta- normal-dextral to dextral-normal faults sedimentary rocks (refer to Table 1 in tion and kinematics (Audemard, 1993, (Píritu -VE-12- and Tacagua -VE-10- Audemard et al. 2005). This approach has Audemard and Singer 1996, Audemard faults); (4) North to NNE left-lateral faults, relied on an inversion method, through 1997b, 2001; Figs. 2 and 4): (1) East-West antithetic to the main east-west faults which the stress tensor has been obtained right-lateral faults (Oca-Ancón Fault Sys- (Quebrada Chacaito faults); (5) ENE rever- from the measured strain. Those tensors tem -VE-01-, Adícora Fault); (2) NW-SE se faults, parallel to fold axis (Nappe fronts, were calculated with either the Etchecopar 488 F. A. AUDEMARD M, A. SINGER P., J.P. SOULAS AND OTHERS

et al. (1981)'s method or the right dihedral Venezuela (Fig. 2). The consistency of the agreement between stress tensors obtained method designed by Angelier and Mechler stress-tensor orientation along northern from microtectonic data and large scale (1977). This latter method is less accurate Venezuela from west to east (from north- neotectonic mapping. σ than that of Etchecopar et al. (1981), which western Colombia to Trinidad) permits the (3)- H in the northern Mérida Andes (Lara is also capable of establishing the qualitati- identification of local variations of the state), in proximity to the Boconó fault, ve shape of the stress tensor ellipsoid stress regime. Most of these local stress tends to become east-west oriented, which through the value of "R", being R defined changes coincide with known transtensio- allows the simultaneous functioning of the σ σ σ σ as ( 2 - 3)/( 1- 3). The principal stress in nal geometries, or occasionally with trans- NE-striking dextral (e.g.: Boconó, Caparo, vertical position indicates the dominant tec- pressional geometries (refer to Audemard et San Simón) faults, the equally-trending tonic regime but R helps to better define it al. 2005 for further details). These changes thrust faults along both Mérida Andes foo- (refer to Ritz 1991, for more details). From are easily identifiable because the stress ten- thills and the north-south striking sinistral this tectonic stress inversion, Audemard et sor orientation remains essentially constant faults (e.g., Valera and Burbusay, among al. (2005) reach the following general con- but their principal stress magnitudes vary several others; Fig. 2). clusions: (stress tensor permutation, where maxi- (4)- As a result of this, the stress field on (1)- northern Venezuela -covering the mum and intermediate stresses may inter- the Maracaibo block (MTB) progressively Falcón basin and the central and eastern change positions). turns counterclockwise from a NNW trend Coast and Interior ranges from west to (2)- The stress tensor calculated by either in the north (Beltrán and Giraldo 1989, east- is characterized by a Plio-Quaternary the Etchecopar et al. (1981)'s automated Audemard 2001, Audemard et al. 2005) to stress tensor of rather uniform and cons- method or the right dihedral method of east-west oriented to the south (Audemard tant orientation throughout. The prevailing Angelier and Mechler (1977) well repre- et al. 1999), making it resemble a folding fan orientations of this tensor are NW to sents the stress field for the present-day with vertex pointing to the SE (Giraldo NNW (145º to 170º) for the maximum kinematics of seven major families of acti- 1990, Audemard and Audemard 2002). The σ horizontal stress ( H) and NE to ENE for ve faults along northern Venezuela: (a) east- orientation of this regional stress field in σ the minimum horizontal stress ( h). The- west right-lateral faults; (b) NW right-lateral western Venezuela results from the super- refore, there is a good consistency among faults, synthetic to the east-west faults; (c) position of the two major neighbouring stress tensors at regional scale. This geolo- NNW normal faults; (d) NW to NNW nor- interplate maximum horizontal stress orien- σ gically derived tensor mostly represents a mal-dextral to dextral-normal faults; (e) tations ( H ): (1) a roughly east-west tren- transcurrent regime (intermediate stress in North-South to NNE-SSW left-lateral ding stress across the Nazca-South America vertical position). Where the Etchecopar et faults, antithetic to the east-west faults; (f) type-B subduction along the pacific coast al.'s method was applied, as in the case of ENE to east-west right-lateral faults -P she- of Colombia and (2) a NNW-SSE oriented the Falcón region, the stress regime can be ars-; and (g) ENE reverse faults, paralleling stress across the southern Caribbean plate constrained better and is of the compressi- the axis of active folds. Spatial configura- boundary (Audemard 2000, Fig. 1). As a ve transcurrent type (Audemard 1991, tion of these brittle tectonic structures indi- result, the Maracaibo block is simultane- 1993, 1997c and 2001). Some authors des- cates that the region is undergoing a trans- ously being shortened along the NW direc- cribe this tectonic regime as transpressive pressional s.l. (compressive-transcurrent) tion (expressed by the vertical growth of and refer to the enlarged sense of the term regime that complies with the simple shear the Santa Marta block and Perijá and and do not restrict its use only to the loca- model proposed by Wilcox et al. (1973). Mérida ranges) and extruded to the NNE lized stress changes introduced by strike- Therefore, this regional configuration is (Audemard 1993, 1998, 2000b, Audemard slip motion in proximity of or along the related to the slightly oblique convergence and Audemard 2002). wrench fault. This stress tensor is highly between the Caribbean and South America oblique to the general east-west trend of plate in the west and almost perfect wren- DISCUSSION AND CON- the major wrench faults of northern Ve- ching in eastern Venezuela with some CLUSIONS nezuela (Oca-Ancón, San Sebastián and El "apparent" transtension (Pérez et al. 2001 Pilar faults). This strong obliquity is respon- and Weber et al. 2001), that is directly res- The stress tensors derived from microtecto- sible, on the one hand for the occurrence of ponsible for east-west trending dextral nic data collected in Plio-Quaternary rocks strain partitioning (right-lateral strike-slip wrenching along northern Venezuela. On and those derived from the spatial configu- along east-west trending faults and trans- the other hand, in northwestern Venezuela ration of Quaternary active faults are in verse shortening in NNW-SSE direction). there is convergence between the Bonaire good agreement. On the one hand, defor- On the other hand, it is also responsible for block (BB) and the Caribbean plate in a mation along the southern Caribbean coast simultaneous left-lateral strike-slip motion process of flat subduction located offshore results from a compressive strike-slip on faults that are slightly oblique to the of the Leeward Antilles islands (LAS), (transpressional s.l.) regime characterized east-west trending dextral faults, as is the which operates in concurrence with the by a NNW-SSE maximum horizontal stress σ σ case of the WSW-ENE-striking Punta Cha- NNE directed extrusion of the Maracaibo ( H= 1) and/or an ENE-WSW minimum ragato and Laguna Grande faults in eastern and Bonaire blocks. Overall there is good Quaternary faults and stress regime of Venezuela 489

σ σ σ ( h= 3 or 2) horizontal stress. This con- and neotectonic studies carried out in Audemard, F. A. 1997b. Tectónica activa de la figuration gives rise to the present activity Venezuela for almost 25 years by the Fun- región septentrional de la cuenca invertida de and kinematics of seven sets of brittle and visis staff. Falcón, Venezuela occidental. Proceedings 8° ductile features: (1) east-west right-lateral Congreso Geológico Venezolano, Porlamar, faults, (2) NW right-lateral faults or synthe- ACKNOWLEDGEMENTS 1:93-100. tic Riedel shears, (3) ENE to east-west dex- Audemard, F. A. 1998. Evolution Géodyna- tral faults or P shears, (4) NNW normal This long-term research would have not mique de la Façade Nord Sud-américaine: faults, (5) almost north-south left-lateral been possible without the continuous fun- Nouveaux apports de l'Histoire Géologique faults or antithetic Riedel shears , (6) ENE ding from Funvisis that allowed most of du Bassin de Falcón, Vénézuéla. Proceedings reverse faults -sub-parallel to fold axes and the dataset collection and generation. 14° Caribbean Geological Conference, Tri- mostly in the subsurface- and (7) associated Perseverance of the personnel of the Earth nidad, 1995, (2): 327-340 ENE trending folds (well-developed in the Sciences Department of FUNVISIS Audemard, F. A. 1999a. Morpho-structural ex- Falcón basin -northwestern Venezuela- and throughout the years made possible this pression of active thrust fault systems in the the Interior range in the east). The main achievement. The Venezuelan Oil Industry humid tropical foothills of Colombia and exceptions to this general configuration are (PDVSA and former affiliates) is also gre- Venezuela. Zeitschrift für Geomorphologie found in eastern Venezuela: the Punta atly acknowledged for providing additional 118, 1-18. Charagato and Laguna Grande faults that funding. Marina Peña is thanked for her Audemard, F. A.1999b. Nueva percepción de la display left-lateral slip along the ENE direc- drawings. This paper is partly a contribu- sismicidad histórica del segmento en tierra de tion. This "apparent" inconsistency may be tion to FONACIT projects G-2002000478 la falla de El Pilar, Venezuela nororiental, a explained by using a ENE-directed block and PI-2003000090, although funding was partir de primeros resultados paleosísmicos. escape model. In most of northern provided by other sources. Proceedings 6° Congreso Venezolano de Sis- Venezuela, brittle deformation obeys the mología e Ingeniería Sísmica, Mérida, (in simple shear model. WORKS CITED IN THE TEXT CD-Rom). On the other hand, the stress field on the Audemard, F. A. 2000. Major Active Faults of Maracaibo block progressively turns coun- Aggarwal, Y. 1983. Neotectonics of the Venezuela. Proceedings 31st International ter-clockwise to become more east-west Southern Caribbean: Recent Data, new ideas. Geological Congress (extended abstract; in oriented, allowing left- and right-lateral slip Acta Científica Venezolana, Abstract 34 CD-Rom) 4 p. Rio de Janeiro. along north-south and NE-SW striking (1):17. Audemard, F. A. 2001. Quaternary tectonics and faults, respectively. This regional stress field Angelier, J. and Mechler, P. 1977. Sur une métho- present stress tensor of the inverted nor- in western Venezuela results from the de graphique de recherche des contraintes thern Falcón Basin, Northwestern Vene- superposition of the two major neighbou- principales également utilisable en tectonique zuela. Journal of Structural Geology 23: 431- ring interplate maximum horizontal stresses et séismologie: la méthode des diedres droits. 453. σ ( H) related to the Nazca plate type-B sud- Bulletin Societé Géologique de France 19(6): Audemard, F. A. 2002. Ruptura de los grandes uction and NNW-SSE oriented stress 1301-1318. sismos históricos venezolanos de los siglos across the southern Caribbean plate boun- Audemard, F. A. 1991. Proyecto suministro XIX y XX revelados por la sismicidad instru- dary. This results in the Maracaibo block Falcón-Zulia (SUFAZ): Actividad cuaternaria mental contemporánea. Proceedings 11° simultaneously being shortened on the NW y caracterización sismogénica de las fallas de Congreso Venezolano de Geofísica 8 p. direction and extruded roughly towards the Lagarto y Rio Seco. Afinamiento de las carac- (CD-Rom format). NNE. terísticas sismogénicas del sistema de fallas de Audemard, F. A. and Singer, A. 1994. Parámetros Wrenching is the dominant geodynamic Oca-Ancón y de Urumaco. Unpublished sismotectónicos para fines de evaluación de process, but it is always accompanied by Funvisis' report for Maraven; 91 p. la amenaza sísmica en el noroccidente de compression of variable magnitude along Audemard, F. A. 1993. Néotectonique, Sis- Venezuela. Proceedings 7° Congreso Vene- strike of the major strike-slip fault system, motectonique et Aléa Sismique du Nord- zolano de Geofísica, 51-56, Caracas. proving that stress (or strain) partitioning is ouest du Vénézuéla (Système de failles Audemard, F. A. and Singer, A. 1996. Active the actuating mechanism. Only locally, d'Oca-Ancón). PhD. thesis, Université Mont- fault recognition in northwestern Venezuela transtension becomes significantly impor- pellier II, France, 369 p. and its seismogenic characterization: neotec- tant, such as in the Cariaco trough and gulf Audemard, F. A. 1996. Paleoseismicity studies on tonic and paleoseismic approach. Geofísica of Paria in association with the El Pilar the Oca-Ancon fault system, northwestern Internacional 35, 245-255. fault. It can now be firmly established that Venezuela. Tectonophysics 259: 67-80. Audemard, F. A. and Singer, A. 1997. La the GPS slip vectors do not only support Audemard, F. A. 1997a. Holocene and Historical Ingeniería de Fallas Activas en Venezuela: the hypothesis of ongoing transpression Earthquakes on the Boconó Fault System, historia y estado del arte. Seminario Interna- along most of this complex plate boundary Southern Venezuelan Andes: Trench Confir- cional de Ingeniería Sísmica: Aniversario del zone, but also tend to confirm most of the mation. Journal of Geodynamics 24(1-4): Terremoto de Caracas de 1967. Universidad active fault slip rates derived from geologic 155-167. Católica Andrés Bello, 11-27, Caracas. 490 F. A. AUDEMARD M, A. SINGER P., J.P. SOULAS AND OTHERS

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