Revista de la Facultad de Ingeniería Universidad Central de Venezuela, Jan 22, 2019
El Macizo de Santander constituye una zona estrategica de la Cordillera Oriental de Colombia por ... more El Macizo de Santander constituye una zona estrategica de la Cordillera Oriental de Colombia por la presencia de recursos minerales e hidricos. El presente estudio aporta criterios de geologia estructural en el area de Charta, donde se identifican fallas que tienen continuidad hacia la parte centro occidental del macizo, y se ubican proyectos mineros, zonas de paramos y fuentes de agua para el consumo humano (mas de un millon de habitantes, incluida la Ciudad de Bucaramanga). A partir de la cartografia geologica y del analisis estructural se obtuvo un modelo de deformacion fragil que explica la distribucion y cinematica de las fallas geologicas y pliegues. Se analizaron las tres direcciones principales del fracturamiento, una hacia el NNO asociada principalmente con fallas de cabalgamiento en estilo estructural de escamacion gruesa y delgada y con vergencia al oriente, y dos direcciones transversales hacia el ONO y NE que exhiben desplazamientos bajo un regimen de rumbo. Con base en la medicion de los atributos de las fracturas como intensidad, densidad y longitud, asi como en el analisis cinematico y en la presencia de afloramientos de agua, se determinaron sectores de alta porosidad secundaria y zonas potencialmente abiertas, relacionadas con corredores o franjas de direccion NE. Por esto, se propone una conexion hidraulica entre las zonas de paramo y las partes bajas, a lo largo de las fracturas NE, las cuales se comportan como canales de flujo de aguas subterraneas y potencialmente de fluidos contaminantes.
The boundary between the Northern Andean block and the South American plate is a first‐order tect... more The boundary between the Northern Andean block and the South American plate is a first‐order tectonic structure in Colombia with historically M > 7 earthquakes. However, details about individual sections of the system remain unknown. We illuminate the seismotectonic of the Algeciras fault by investigating an earthquake sequence that started on 24 December 2019. Using seismic networks at region, we estimate foreshocks and aftershocks focal mechanisms, local stress field, kinematic slip models of the largest events, and Coulomb stress changes. We integrate seismological and morphostructural observations to characterize source properties and reinterpret local faults. Two mainshocks (doublet of Mw 6.0 and 5.8) occurred within 16 min, rupturing just a few kilometers from each other. Discrimination of causative faults among the centroid moment‐tensor nodal planes is difficult because the focal zone is a complex tectonic environment. The focal mechanisms and the local stress field obtained are consistent with a regional NE trending dextral transpressive shear. The relocated aftershocks show a cluster with an L‐shaped pattern concentrated in a ∼7 × 7 km area. Our model defines the Algeciras fault with two structural styles for its northern termination. The NW part is characterized by a duplex‐style of right‐lateral strike‐slip with inner secondary faults of the same sense of movement, and the SE zone by a domino‐style system with inner minor faults of sinistral kinematics. The earthquake doublet is in the zone characterized by the duplex style. In contrast, the southern part of the aftershocks is located in the zone characterized by the domino style.
La Falla de Ibagué presenta rasgos contundentes de actividad neotectónica asociados con su trazo,... more La Falla de Ibagué presenta rasgos contundentes de actividad neotectónica asociados con su trazo, los cuales la definen como una estructura potencialmente productora de grandes sismos. En el campo cercano existen importantes centros poblados del país con cerca de 13 millones de habitantes (Ibagué, Bogotá, Armenia, Pereira y Manizales son los más importantes). Por esta razón, el panorama de la amenaza sísmica asociada a esta estructura es evaluado por medio de una combinación de diferentes técnicas para conocer su verdadero potencial sismogénico. Las disciplinas de la neotectónica, como la morfotectónica y la paleosismología, son imprescindibles para ampliar el tiempo de observación y para determinar el grado de actividad sísmica derivada de una estructura geológica. La morfotectónica estudia las geoformas creadas por las fallas activas, particularmente las fallas sismogénicas; la paleosismología integra estudios geomorfológicos y estratigráficos por medio de la correlación de las geoformas y los procesos de su formación asociadas a las fallas activas y su correspondiente ambiente deposicional (McCalpin, 1996). Con base en la importancia manifiesta de la Falla de Ibagué en el esquema actual de actividad sísmica del país y en la incertidumbre de la evaluación de su potencial, se proyectó un estudio completo de cartografía y caracterización sismotectónica y se programó, en el estado final, la apertura de una trinchera de exploración paleosismológica que permitiera determinar los parámetros sísmicos en una localidad de la falla. Para conocer de forma adecuada el contexto tectónico y sismológico de la estructura, sería necesario abrir otras trincheras a lo largo de la falla. En este trabajo se presentan los resultados de las fases cumplidas para la selección del sitio de trinchera, durante las cuales se obtuvo el conocimiento básico de la geometría y la cinemática de la falla; además, se presenta la metodología y los resultados obtenidos en la apertura de la trinchera en la Falla de Ibagué.
Abstract Morphometric analysis is widely used in tectonic geomorphology as a useful method for id... more Abstract Morphometric analysis is widely used in tectonic geomorphology as a useful method for identifying fold activity in terms of its lateral and vertical growth. This study evaluates the recent tectonic activity and lateral propagation of the Los Cobardes anticline (LCA), which built up the Yariguies Range, from morphometric characterization, a structural kinematic analysis, and fieldwork. The study area is located west of the Colombian Eastern Cordillera in a tectonically active region bounded by longitudinal tectonically inverted reverse structures (e.g., the Suarez Fault) with minor transverse faults and the LCA as the central fold of the Yariguies Anticlinorium. A comparison among the precipitation data, lithology, and the morphometric indexes leads us to conclude that for the LCA, recent tectonics drive fold activity. Based on the LCA’s geomorphology and the kinematic analysis derived from fault-slip data, we define three independent fold segments bounded by transverse zones: LCA-A, LCA-B, and LCA-C. Of these, the first two show evidence of lateral propagation toward the southwest, which is closely related to the activity of the Suarez Fault and inherited transverse structures. We found qualitative and quantitative geomorphologic evidence of southwestward propagation: wind and water gaps decreasing in elevation, drainages partially flowing in the direction opposite to the regional trend, and low concavity values for normalized profiles (from -40.49 to 11.76) and Vf (from 0.07 to 0.13). Assisted by published low-temperature thermochronology and seismotectonic data, we demonstrate that the LCA has been growing since the Pliocene and remains active, accommodating deformation in a transpressive stress state. Our findings could serve as a reference to study active fold growth and its structural drivers in known tectonically inverted basins, such as the foreland thrust belt in Argentina, the High Atlas Mountains in Morocco, and the Central Mountain Range of Taiwan, among others.
Abstract The integration of drainage analysis and topographic metrics provides excellent tools to... more Abstract The integration of drainage analysis and topographic metrics provides excellent tools to assess the Quaternary tectonic activity modeling landscape evolution in evolving orogens. Furthermore, detecting active structures through the geomorphological analysis of landscapes helps to identify potentially seismogenic structures that could impact the socio-economic conditions in developing countries. Therefore, this paper presents a tectonic geomorphology study conducted on the Santander Massif (SM, Colombian Eastern Cordillera) and surrounding areas. The SM has structures with reported Quaternary activity such as the Bucaramanga, Morro Negro-Las Mercedes, and Chitaga faults, which summed to a poorly-constrained paleosismological history with significant shallow events is the prime incentive of this work. Our study is based on the acquisition of topographic data through swath profiles, local relief, slope variability, filtered topography, minimum bulk erosion, which along with geomorphic indices like the normalized concavity steepness (ksn), the hypsometric integral (HI), the ratio valley floor width to valley height (Vf) and normalized river profiles provided new insights on the recent landscape evolution in this part of the Northern Andes. We compared published apatite fission tracks (AFT) data for the study area with the uplift pattern deciphered from the geomorphic indices to detect the consistency in exhumation and denudation processes both in the long and short-term. Consequently, the central SM, as well as the faulted block between the Bucaramanga and Guamalito faults, evidence a highly-incised landscape with local relief values exceeding the 1500 m, then, responding with a sharp incision to recent surface uplift. Interestingly, this uplift pattern in central SM matches with published AFT data and is related to Neogene exhumation events controlled by secondary structures like the Surata Fault. We attribute this exhumation event, and accelerated denudation rates within the SM, to the influence exerted by the “collision” between the SM and the Pamplona Indenter, leading to the unroofing of basement rocks at the deformation front (e.g., the Vetas High) and the topographic building of the range. For the upthrown block (hanging wall) of the Bucaramanga Fault, the occurrence of poorly-graded river profiles with an average concavity factor of 12.01, as well as irregular hypsometric curves with convex lower reaches, reinforce the hypothesis that late Cenozoic topographic rejuvenation in the SM was also forced by the tectonic activity of the Bucaramanga Fault. We expect empirical uplift rates >0.08 mm/yr (very high to high tectonic activity) for the mountain front encompassed between La Esperanza and Bucaramanga localities. We state this assumption since the mountain front delimited by the structure mentioned above is quite straight, it preserves remarkable morphostructural features and displays V-shaped valleys with an average Vf index of 0.38. This uplift rate is in good agreement with recent thermochronological exhumation rates (0.1 to > 0.3 mm/yr) published by Siravo et al. (2019). Higher uplift rates associated with the Bucaramanga Fault were also constrained with the erosion proxy index, i.e., the ksn index. High ksn values (above 128) were observed following a linear pattern, which in turn seems controlled by the main trace of the Bucaramanga Fault. For instance, the river system draining the western piedmont of the SM, near Aguachica, records slope-break knickpoints that we interpret as evidence of an incisional wave migrating upstream and adjusting a late Neogene uplift event associated with the Bucaramanga Fault. Conversely, the northern SM presents variable tectonic activity with the inner part, east of the Guamalito Fault, presenting low tectonic activity with little surface uplift and dominant strike-slip kinematics. We recognize the Ocana-Abrego zone as a relict landscape with well-preserved non-consolidated deposits that may record the initial exhumation and denudational pulses of the SM during the Andean Orogeny.
Revista de la Facultad de Ingeniería Universidad Central de Venezuela, Jan 22, 2019
El Macizo de Santander constituye una zona estrategica de la Cordillera Oriental de Colombia por ... more El Macizo de Santander constituye una zona estrategica de la Cordillera Oriental de Colombia por la presencia de recursos minerales e hidricos. El presente estudio aporta criterios de geologia estructural en el area de Charta, donde se identifican fallas que tienen continuidad hacia la parte centro occidental del macizo, y se ubican proyectos mineros, zonas de paramos y fuentes de agua para el consumo humano (mas de un millon de habitantes, incluida la Ciudad de Bucaramanga). A partir de la cartografia geologica y del analisis estructural se obtuvo un modelo de deformacion fragil que explica la distribucion y cinematica de las fallas geologicas y pliegues. Se analizaron las tres direcciones principales del fracturamiento, una hacia el NNO asociada principalmente con fallas de cabalgamiento en estilo estructural de escamacion gruesa y delgada y con vergencia al oriente, y dos direcciones transversales hacia el ONO y NE que exhiben desplazamientos bajo un regimen de rumbo. Con base en la medicion de los atributos de las fracturas como intensidad, densidad y longitud, asi como en el analisis cinematico y en la presencia de afloramientos de agua, se determinaron sectores de alta porosidad secundaria y zonas potencialmente abiertas, relacionadas con corredores o franjas de direccion NE. Por esto, se propone una conexion hidraulica entre las zonas de paramo y las partes bajas, a lo largo de las fracturas NE, las cuales se comportan como canales de flujo de aguas subterraneas y potencialmente de fluidos contaminantes.
The boundary between the Northern Andean block and the South American plate is a first‐order tect... more The boundary between the Northern Andean block and the South American plate is a first‐order tectonic structure in Colombia with historically M > 7 earthquakes. However, details about individual sections of the system remain unknown. We illuminate the seismotectonic of the Algeciras fault by investigating an earthquake sequence that started on 24 December 2019. Using seismic networks at region, we estimate foreshocks and aftershocks focal mechanisms, local stress field, kinematic slip models of the largest events, and Coulomb stress changes. We integrate seismological and morphostructural observations to characterize source properties and reinterpret local faults. Two mainshocks (doublet of Mw 6.0 and 5.8) occurred within 16 min, rupturing just a few kilometers from each other. Discrimination of causative faults among the centroid moment‐tensor nodal planes is difficult because the focal zone is a complex tectonic environment. The focal mechanisms and the local stress field obtained are consistent with a regional NE trending dextral transpressive shear. The relocated aftershocks show a cluster with an L‐shaped pattern concentrated in a ∼7 × 7 km area. Our model defines the Algeciras fault with two structural styles for its northern termination. The NW part is characterized by a duplex‐style of right‐lateral strike‐slip with inner secondary faults of the same sense of movement, and the SE zone by a domino‐style system with inner minor faults of sinistral kinematics. The earthquake doublet is in the zone characterized by the duplex style. In contrast, the southern part of the aftershocks is located in the zone characterized by the domino style.
La Falla de Ibagué presenta rasgos contundentes de actividad neotectónica asociados con su trazo,... more La Falla de Ibagué presenta rasgos contundentes de actividad neotectónica asociados con su trazo, los cuales la definen como una estructura potencialmente productora de grandes sismos. En el campo cercano existen importantes centros poblados del país con cerca de 13 millones de habitantes (Ibagué, Bogotá, Armenia, Pereira y Manizales son los más importantes). Por esta razón, el panorama de la amenaza sísmica asociada a esta estructura es evaluado por medio de una combinación de diferentes técnicas para conocer su verdadero potencial sismogénico. Las disciplinas de la neotectónica, como la morfotectónica y la paleosismología, son imprescindibles para ampliar el tiempo de observación y para determinar el grado de actividad sísmica derivada de una estructura geológica. La morfotectónica estudia las geoformas creadas por las fallas activas, particularmente las fallas sismogénicas; la paleosismología integra estudios geomorfológicos y estratigráficos por medio de la correlación de las geoformas y los procesos de su formación asociadas a las fallas activas y su correspondiente ambiente deposicional (McCalpin, 1996). Con base en la importancia manifiesta de la Falla de Ibagué en el esquema actual de actividad sísmica del país y en la incertidumbre de la evaluación de su potencial, se proyectó un estudio completo de cartografía y caracterización sismotectónica y se programó, en el estado final, la apertura de una trinchera de exploración paleosismológica que permitiera determinar los parámetros sísmicos en una localidad de la falla. Para conocer de forma adecuada el contexto tectónico y sismológico de la estructura, sería necesario abrir otras trincheras a lo largo de la falla. En este trabajo se presentan los resultados de las fases cumplidas para la selección del sitio de trinchera, durante las cuales se obtuvo el conocimiento básico de la geometría y la cinemática de la falla; además, se presenta la metodología y los resultados obtenidos en la apertura de la trinchera en la Falla de Ibagué.
Abstract Morphometric analysis is widely used in tectonic geomorphology as a useful method for id... more Abstract Morphometric analysis is widely used in tectonic geomorphology as a useful method for identifying fold activity in terms of its lateral and vertical growth. This study evaluates the recent tectonic activity and lateral propagation of the Los Cobardes anticline (LCA), which built up the Yariguies Range, from morphometric characterization, a structural kinematic analysis, and fieldwork. The study area is located west of the Colombian Eastern Cordillera in a tectonically active region bounded by longitudinal tectonically inverted reverse structures (e.g., the Suarez Fault) with minor transverse faults and the LCA as the central fold of the Yariguies Anticlinorium. A comparison among the precipitation data, lithology, and the morphometric indexes leads us to conclude that for the LCA, recent tectonics drive fold activity. Based on the LCA’s geomorphology and the kinematic analysis derived from fault-slip data, we define three independent fold segments bounded by transverse zones: LCA-A, LCA-B, and LCA-C. Of these, the first two show evidence of lateral propagation toward the southwest, which is closely related to the activity of the Suarez Fault and inherited transverse structures. We found qualitative and quantitative geomorphologic evidence of southwestward propagation: wind and water gaps decreasing in elevation, drainages partially flowing in the direction opposite to the regional trend, and low concavity values for normalized profiles (from -40.49 to 11.76) and Vf (from 0.07 to 0.13). Assisted by published low-temperature thermochronology and seismotectonic data, we demonstrate that the LCA has been growing since the Pliocene and remains active, accommodating deformation in a transpressive stress state. Our findings could serve as a reference to study active fold growth and its structural drivers in known tectonically inverted basins, such as the foreland thrust belt in Argentina, the High Atlas Mountains in Morocco, and the Central Mountain Range of Taiwan, among others.
Abstract The integration of drainage analysis and topographic metrics provides excellent tools to... more Abstract The integration of drainage analysis and topographic metrics provides excellent tools to assess the Quaternary tectonic activity modeling landscape evolution in evolving orogens. Furthermore, detecting active structures through the geomorphological analysis of landscapes helps to identify potentially seismogenic structures that could impact the socio-economic conditions in developing countries. Therefore, this paper presents a tectonic geomorphology study conducted on the Santander Massif (SM, Colombian Eastern Cordillera) and surrounding areas. The SM has structures with reported Quaternary activity such as the Bucaramanga, Morro Negro-Las Mercedes, and Chitaga faults, which summed to a poorly-constrained paleosismological history with significant shallow events is the prime incentive of this work. Our study is based on the acquisition of topographic data through swath profiles, local relief, slope variability, filtered topography, minimum bulk erosion, which along with geomorphic indices like the normalized concavity steepness (ksn), the hypsometric integral (HI), the ratio valley floor width to valley height (Vf) and normalized river profiles provided new insights on the recent landscape evolution in this part of the Northern Andes. We compared published apatite fission tracks (AFT) data for the study area with the uplift pattern deciphered from the geomorphic indices to detect the consistency in exhumation and denudation processes both in the long and short-term. Consequently, the central SM, as well as the faulted block between the Bucaramanga and Guamalito faults, evidence a highly-incised landscape with local relief values exceeding the 1500 m, then, responding with a sharp incision to recent surface uplift. Interestingly, this uplift pattern in central SM matches with published AFT data and is related to Neogene exhumation events controlled by secondary structures like the Surata Fault. We attribute this exhumation event, and accelerated denudation rates within the SM, to the influence exerted by the “collision” between the SM and the Pamplona Indenter, leading to the unroofing of basement rocks at the deformation front (e.g., the Vetas High) and the topographic building of the range. For the upthrown block (hanging wall) of the Bucaramanga Fault, the occurrence of poorly-graded river profiles with an average concavity factor of 12.01, as well as irregular hypsometric curves with convex lower reaches, reinforce the hypothesis that late Cenozoic topographic rejuvenation in the SM was also forced by the tectonic activity of the Bucaramanga Fault. We expect empirical uplift rates >0.08 mm/yr (very high to high tectonic activity) for the mountain front encompassed between La Esperanza and Bucaramanga localities. We state this assumption since the mountain front delimited by the structure mentioned above is quite straight, it preserves remarkable morphostructural features and displays V-shaped valleys with an average Vf index of 0.38. This uplift rate is in good agreement with recent thermochronological exhumation rates (0.1 to > 0.3 mm/yr) published by Siravo et al. (2019). Higher uplift rates associated with the Bucaramanga Fault were also constrained with the erosion proxy index, i.e., the ksn index. High ksn values (above 128) were observed following a linear pattern, which in turn seems controlled by the main trace of the Bucaramanga Fault. For instance, the river system draining the western piedmont of the SM, near Aguachica, records slope-break knickpoints that we interpret as evidence of an incisional wave migrating upstream and adjusting a late Neogene uplift event associated with the Bucaramanga Fault. Conversely, the northern SM presents variable tectonic activity with the inner part, east of the Guamalito Fault, presenting low tectonic activity with little surface uplift and dominant strike-slip kinematics. We recognize the Ocana-Abrego zone as a relict landscape with well-preserved non-consolidated deposits that may record the initial exhumation and denudational pulses of the SM during the Andean Orogeny.
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