Resultados preliminares del primer estudio paleosismológico a lo largo de la falla de Bucaramanga, Colombia

The Bucaramanga Fault is the fault in Colombia with the strongest physiographic expression. It extends from Aguachica in the north southward to Bucaramanga and beyond. Abundant morphotectonic indices testify to a high degree of activity during the Quaternary. A recent detailed regional study along the main fault corridor has identified several promising locations with potential for paleoseismologic trench studies. The site actually selected was situated in a limestone quarry at 4,5 km north of Bucaramanga town on the north bank of the Surata river. It concerns a small tectonic basin in a hanging valley situated 250 m to the west of the main Bucaramanga Fault and is filled with a series of colluvial wedges and fine grained lacustrine deposits with abundant organic material. Detailed logging of the outcrop face at a scale of 1:10 was carried out and seventeen samples were taken from the organic rich levels for radiocarbon dating. Basin evolution is controlled by movement of the principal fault trace in which each sedimentary level is a registration of co-seismic subsidence and represents the stratigraphic evidence of pre-historic earthquakes. The result of radiocarbon dating show ages that range from 8300-930 y/BP and a preliminary interpretation suggests the occurrence of 8 holocene seismic events during the last 8300 years and magnitudes in the order of 6,5-7,0 Ms.La Falla de Bucaramanga es la de mayor expresión fisiográfica en Colombia, se extiende desde Aguachica, en el norte, hacia Bucaramanga, en el Sur, y exhibe indicios morfotectónicos que atestiguan un alto grado de actividad durante el Cuaternario. Un reciente levantamiento neotectónico detallado en el corredor de la falla permitió identificar sitios con potencial paleosismológico. El sitio seleccionado está en una cantera de calizas a 4,5 kilómetros al norte de Bucaramanga, en el flanco norte del río Suratá. Corresponde a una cuenca colgada de origen tectónico a 250 m al oeste de la traza principal, rellenada por cuñas coluviales y una secuencia reciente de horizontes lacustre finos con material orgánico. Se realizó un levantamiento detallado a escala 1:10 y se tomaron diecisiete muestras que cubren el paquete de sedimentos orgánicos. Se interpreta como una cuenca tectónica o "sagpond" controlada por la falla principal, donde cada horizonte sedimentario registra el hundimiento co-sísmico, es decir, la evidencia estratigráfica de sismos prehistóricos. Los resultados de C14 oscilan entre 8300-930 años-BP, y su interpretación preliminar apunta a la ocurrencia de 8 sismos holocenos con intervalos de recurrencia de aproximadamente1000 años y magnitudes entre 7,0-7,4 Ms

Inventario de Daños y Efectos Geológicos Co y/o Post-Sísmicos del Sismo Ocurrido el 18 de mayo de 1875, en la Frontera entre Colombia y Venezuela

On the border between Colombia and Venezuela, have occurred seismic events with important records of damage in both countries. In this paper, we study the historical earthquake that took place on May 18, 1875 between 11.15 and 11.30 in the morning (the time was the same for communities in both countries since there was no time zone difference), which is catalogued as a border earthquake due to the report of damages in the cities of both nations. The community of San José de Cúcuta, current capital of the Northern State of Santander, Colombia, registered the greatest number of deaths and damage to buildings. An inventory of the geological damage and co -seismic and postseismic effects was created based on information of previous studies and data obtained from archival primary sources from Colombia and Venezuela. The result is a bi-national database, which includes the summaries of historical descriptions with the effects in the persons and objects, the geological damages and effects observed during the seismic event. These data has led to the creation of a table of MM and EMS-98 intensities, which enables the identification and delimitation of the regions of greater damages. The maximum level intensity is I=10 in the cities of San José de Cúcuta, Villa del Rosario, Pueblo de Cúcuta (San Luis) in Colombia and San Antonio, San Juan de Ureña in Venezuela. Moreover, we formulated a table of intensities using the ESI-2007 INQUA scale, based on the information of geological observations described in historical documents. These data are related to the epicentral zone with an approximate radius of 30 km.Published105-2635T. Sismologia, geofisica e geologia per l'ingegneria sismicaN/A or not JC

Inventario de sismos con reportes de daños y efectos geológicos co-sísmicos en la frontera colombo-venezolana

La zona evaluada en la frontera colombo-venezolana, comprende los estados Táchira y suroeste de Mérida en Venezuela, y por Colombia el extremo oriental de los departamentos del Norte y Sur de Santander, es una región tectónicamente compleja, atravesada por sistemas de fallas activas que forman parte de la estructura conocida como el Indentor o Punzón de Pamplona. La metodología utilizada se basó en la búsqueda y recopilación de información a partir de fuentes primarias y secundarias, se tomó en cuenta la historia social, económica y política transcurrida en los cinco siglos de historia como región fronteriza, y de igual manera implicó visitas de campo a los archivos regionales y se revisaron los catálogos de sismos históricos e instrumentales de ambas naciones. A partir de los datos recopilados, se obtuvo un inventario de sismos con reporte de daños en edificaciones y manifestación de efectos geológicos co-sísmicos, el cual aglutina 24 entradas, de los cuales 13 eventos se ubican en Venezuela y 11 en Colombia. Es el primer inventario con datos históricos y contemporáneos binacional y servirá como base para futuras evaluaciones y/o reevaluaciones macrosísmicas, teniendo presente que el límite fronterizo no es una barrera

Quaternary shortening at the orogenic front of the Central Andes of Argentina: the Las Peñas Thrust System

The NNW-trending Las Peñas Thrust System is one of the key structures along the Andean orogenic front between 32°15′ and 32°40′S in the Southern Precordillera of Argentina. This east-verging structure crops out over a distance of c. 40 km and provides one of the best opportunities for a detailed field survey of Quaternary thrusting in the Andean frontal deformation zone. We present a systematic description of the geometry and geomorphic signatures of the main thrust deformation zone, which emplaces Neogene rocks over Quaternary alluvium, and usually behaves as a blind propagating thrust into the youngest (Late Pleistocene–Holocene) alluvial deposits. The Las Peñas Thrust System is understood to represent the latest stage of the eastward migration of an imbricated fan structure, which has driven the neotectonic uplift of the Las Peñas–Las Higueras range. Excellent outcrops provided by well-incised creek outlets reveal that the thrust system is made up either by a single fault surface or by two or more frontal splays. Several sections along its length can be differentiated on the basis of thrust geometries and/or morphotectonic features. The northern sections are characterized by isolated outcrops of Neogene rocks in the hanging wall, surrounded by alluvial bajadas. Remnants of fold limbs scarps depict the geomorphic signature of the thrust propagation into the Quaternary layers, although the preserved topographic relief always underestimates the cumulated thrust slip during the Quaternary. The southern part of this thrust system is defined by a frontal range, cored by a transposed south-plunging anticline in bedrock. Our observations suggest a dynamic and unsteady interaction between thrust propagation and sedimentation/erosion processes along the thrust trace during deposition of the Quaternary alluvial layers.Fil: Costa, Carlos H.. Universidad Nacional de San Luis; ArgentinaFil: Ahumada, Emilio Antonio. Universidad Nacional de San Luis; ArgentinaFil: Gardini, Carlos Enrique. Universidad Nacional de San Luis; ArgentinaFil: Vazquez, Fabricio Rodrigo. Universidad Nacional de San Luis; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Diederix, Hans. Servicio Geológico Colombiano; Colombi

Resultados preliminares del primer estudio paleosismológico a lo largo de la falla de Bucaramanga, Colombia

The Bucaramanga Fault is the fault in Colombia with the strongest physiographic expression. It extends from Aguachica in the north southward to Bucaramanga and beyond. Abundant morphotectonic indices testify to a high degree of activity during the Quaternary. A recent detailed regional study along the main fault corridor has identified several promising locations with potential for paleoseismologic trench studies. The site actually selected was situated in a limestone quarry at 4,5 km north of Bucaramanga town on the north bank of the Surata river. It concerns a small tectonic basin in a hanging valley situated 250 m to the west of the main Bucaramanga Fault and is filled with a series of colluvial wedges and fine grained lacustrine deposits with abundant organic material. Detailed logging of the outcrop face at a scale of 1:10 was carried out and seventeen samples were taken from the organic rich levels for radiocarbon dating. Basin evolution is controlled by movement of the principal fault trace in which each sedimentary level is a registration of co-seismic subsidence and represents the stratigraphic evidence of pre-historic earthquakes. The result of radiocarbon dating show ages that range from 8300-930 y/BP and a preliminary interpretation suggests the occurrence of 8 holocene seismic events during the last 8300 years and magnitudes in the order of 6,5-7,0 Ms.La Falla de Bucaramanga es la de mayor expresión fisiográfica en Colombia, se extiende desde Aguachica, en el norte, hacia Bucaramanga, en el Sur, y exhibe indicios morfotectónicos que atestiguan un alto grado de actividad durante el Cuaternario. Un reciente levantamiento neotectónico detallado en el corredor de la falla permitió identificar sitios con potencial paleosismológico. El sitio seleccionado está en una cantera de calizas a 4,5 kilómetros al norte de Bucaramanga, en el flanco norte del río Suratá. Corresponde a una cuenca colgada de origen tectónico a 250 m al oeste de la traza principal, rellenada por cuñas coluviales y una secuencia reciente de horizontes lacustre finos con material orgánico. Se realizó un levantamiento detallado a escala 1:10 y se tomaron diecisiete muestras que cubren el paquete de sedimentos orgánicos. Se interpreta como una cuenca tectónica o "sagpond" controlada por la falla principal, donde cada horizonte sedimentario registra el hundimiento co-sísmico, es decir, la evidencia estratigráfica de sismos prehistóricos. Los resultados de C14 oscilan entre 8300-930 años-BP, y su interpretación preliminar apunta a la ocurrencia de 8 sismos holocenos con intervalos de recurrencia de aproximadamente1000 años y magnitudes entre 7,0-7,4 Ms

Memorias IX Congreso Geológico Venezolano (1)

Memorias del IX Congreso Geológico Venezolan