Evolución tectónica y estructural de la zona de Falla de El Salvador: aplicaciones a la amenaza sísmica

Tesis inédita presentada en la Universidad Complutense de Madrid, Facultad de Ciencias Geológicas, Departamento de Geodinámica, leída el 21-10-2015Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEunpu

From transpressional to transtensional tectonics in Northern Central America

The Central American Volcanic Arc (CAVA) is located at the western margin of the Caribbean plate, over the Chortís Block, spanning from Guatemala to Costa Rica. The CAVA is associated to the subduction of the Cocos plate under the Caribbean plate at the Middle America Trench. Our study is focused in the Salvadorian CAVA segment, which is tectonically characterized by the presence of the El Salvador Fault Zone (ESFZ), part of the western boundary of a major block forming the Caribbean plate (the Chortis Block). The structural evolution of the western boundary of the Chortis Block, particularly in the CAVA crossing El Salvador remains unknown. We have done a kinematic analysis from seismic and fault slip data and combined our results with a review of regional previous studies. This approach allowed us to constrain the tectonic evolution and the forces that control the deformation in northern Central America. Along the active volcanic arc we identified active transtensional deformation. On the other hand, we have identified two deformation phases in the back arc region: A first one of transpressional wrenching close to simple shearing (Miocene); and a second one characterized by almost E-W extension. Our results reveal a change from transpressional to transtensional shearing coeval with a migration of the volcanism towards the trench in Late Miocene times. This strain change could be related with a coupled to decoupled transition on the Cocos – Caribbean subduction interface, which could be related to a slab roll-back of the Cocos Plate beneath the Chortis Block. The combination of different degrees of coupling on the subduction interface, together with a constant relative eastward drift of the Caribbean Plate, control the deformation style along the western boundary of the Chortis Block

Main crustal seismic sources in El Salvador

We present a map and a data set containing information about intra-plate seismic sources in El Salvador. These are the results of the field campaigns and data analysis carried out by the research group of Planetary Geodinamics, Active Tectonics and Related Risks from Complutense University of Madrid during the last 12 years. We include two maps, the first map contains 1405 fault traces with evidences of Quaternary activity derived form morphometric, paleoseismological and geomorphological analysis together with field data mapping carried in El Salvador. The second map is a synthesis of the 29 intra-plate seismic sources selected from the quaternary faults map. The geometry of these sources was simplified and we also include a table where some available data of the proposed sources are included, such as their name, orientation, length and slip-rate. For further interpretation and discussion of these sources see (Alonso-Henar et al., 2018) [1, doi.org/10.1016/j.enggeo.2018.06.015]This research was supported by the project“ QUAKESTEP”(CGL2017–83931-C3-1-P) founded by the Spanish Ministry of Science, Innovation and Universities. We are grateful to our colleagues atDGOA-MARN (Observatorio Ambiental del Ministerio de Medio Ambiente y Recursos Naturales de ElSalvador): Manuel Díaz, Walter Hernandez and Douglas Hernández for their assistance. Figures were produced using GMT softwar

Complete Strain Record of a Highly Asymmetric Shear Zone: From Fault Core Gouges to Surface Rupture of Historical Earthquakes in the Alhama de Murcia Fault (SE Iberian Peninsula)

Classical models of fault rock architecture point to a relatively simple and symmetric architecture of a fault zone, where the fault core is a narrow foliated cataclasite (few centimeters) bounded by a thick damage zone developed cutting through host rocks. Those models are far from the studied fault rocks developed in the Alhama de Murcia Fault (AMF), SE Spain, where fault core is in contact with an almost no deformed hosting rock at one side and to a wide damage zone towards the opposite boundary. The AMF is an active shear zone and the source of destructive recent and historical earthquakes. It has more than 10 km accumulated slip, and it develops a more than 100 meters wide shear zone with fault rocks that have been continuously sampled and analyzed combining a drill core from a 174 m deep vertical borehole, six trenches excavation, and outcrop surfaces cleaning. Hand specimen and microanalyses were used to classify the fault rock in deformation domains in a strongly heterogeneous shear zone according to its lithologies and structural features. It ranges from 10 to 30 meters wide fault core, where steady strain occurs, to an intensely deformed damage zone where strain is concentrated along discrete gouge bands. Trenching also showed a surface rupture that offsets Arabic archaeological remains related to the 1674 catastrophic event occurred in Lorca (Murcia). Steady homogeneous deformation was found in the areas closest to the hanging wall, in the fault core, where Lower Paleozoic Schists are the potolith of ultrafault gouges. As deformation increased, the shear zone involved Permian-Triasic basement rocks and Miocene sedimentary rocks in heterogeneous deformation domains. In the lower domains, strain is located in anastomosing shear bands which are spatially related with a surface seismic rupture of the 1674 destructive earthquake

Push-pull driving of the Central America Forearc in the context of the Cocos-Caribbean-North America triple junction

Different kinematic models have been proposed for the triple junction between the North American, Cocos and Caribbean plates. The two most commonly accepted hypotheses on its driving mechanism are (a) the North American drag of the forearc and (b) the Cocos Ridge subduction push. We present an updated GPS velocity field which is analyzed together with earthquake focal mechanisms and regional relief. The two hypotheses have been used to make kinematic predictions that are tested against the available data. An obliquity analysis is also presented to discuss the potential role of slip partitioning as driving mechanism. The North American drag model presents a better fit to the observations, although the Cocos Ridge push model explains the data in Costa Rica and Southern Nicaragua. Both mechanisms must be active, being the driving of the Central American forearc towards the NW analogous to a push-pull train. The forearc sliver moves towards the west-northwest at a rate of 12–14 mm/yr, being pinned to the North American plate in Chiapas and western Guatemala, where the strike-slip motion on the volcanic arc must be very small

New paleoseismic data for the Alhama de Murcia Fault in the La Salud alluvial fan (Lorca-Totana segment) Betic Cordillera

La Falla de Alhama de Murcia (FAM) es una falla de desgarre sinestral y cierta componente inversa, que fue la responsable del terremoto más catastrófico producido en España en los últimos 50 años, el terremoto de Lorca de 2011 (Mw 5.2). En este trabajo se presenta el estudio de dos trincheras paleosísmicas excavadas en la superficie del abanico aluvial de La Salud que se encuentra cubriendo la traza de la FAM en el sector oriental del segmento Lorca-Totana. La excavación de las trincheras se apoya en la realización de una prospección geofísica mediante tomografía eléctrica y perfiles GPR con el objetivo de obtener nuevos datos de recurrencia sísmica en esta zona de la falla. Tanto las trincheras como los datos geofísicos son coherentes con la existencia de un plano de falla buzando 30º hacia el sur que deforma visiblemente los últimos depósitos del abanico. Las trincheras nos indican la ocurrencia de entre 3 y 6 eventos paleosísmicos de ruptura superficial en los últimos 31 ky.The Alhama de Murcia Fault (FAM) is a left-lateral strike-slip fault with reverse component. This fault is located in the southeast of Spain and produces the 2011 Lorca earthquake (Mw 5.2), that was the most catastrophic earthquake occurred in Spain in the last 50 years. In this paper we present the analysis of two paleoseismic trenches excavated in La Salud alluvial fan, with the aim to obtain new recurrence data for the eastern section of the Lorca- Totana segment of the fault. The structure that we observed in the trenches is recognizable in the electric tomography and GPR profiles undertaken in the study area. Both the paleoseismic trenches and the geophysics analysis are consistent with the existence of a fault plane dipping 30º to the south. This fault plane deforms the younger fluvial fan deposits. The paleoseismic study indicates the existence of between 3 and 6 surface rupture events in the last 31 ka for this strand of the fault.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)pu

New evidences of historical surface rupture on the Alhama de Murcia fault: implications for seismic hazard

Reunión Ibérica sobre Fallas Activas y Paleosismología (3ª. 2018. Alicante). - Texto en inglés con resumen y palabras claves en inglés y españolThe date of the last large event occurred in a fault segment is of great importance in seismic hazard assessment, especially when time-dependent models are considered. Eight of the twelve destructive earthquakes occurred in the eastern Betic Cordillera since 16th century, are located less than 10 km away from the Alhama de Murcia fault (AMF). Up to now, ground surface geological evidence to associate these events with the activity of specific fault segments has not been identified. In this work we present the first geological evidence of the catastrophic 1674 event occurred at Lorca (SE Spain). The excavations at La Torrecilla creek exposed archaeological remains from the Islamic period affected by 55+/-20 cm offset by the AMF fault. This supports the occurrence of earthquakes with surface rupture in the historical period on the Alhama de Murcia Fault and reinforces the results obtained in the previous paleoseismological works. The theoretical scenarios of maximum magnitudes and recurrence time obtained by combining this historical event with the fault slip rate, given the accumulated slip deficit, support that the seismic hazard associated with maximum magnitude events in this section of AMF could be greater than previously thought = La edad del último gran terremoto en un segmento de una falla sismogénica es un parámetro clave para los cálculos de peligrosidad sísmica, especialmente en los cálculos basados en modelos dependientes del tiempo. Ocho de los doce terremotos destructivos ocurridos en las cordilleras Béticas orientales desde el siglo XVI están localizados a menos de 10 km de la traza superficial de la Falla de Alhama de Murcia (AMF). Hasta ahora no se han identificado evidencias geológicas de ruptura superficial asociada a estos eventos que permitan asociarlos a segmentos específicos de la AMF. En este trabajo se presentan evidencias geológicas de ruptura superficial asociada al terremoto de Lorca de 1674. Las excavaciones paleosísmicas realizadas en la rambla de La Torrecilla han expuesto restos de una acequia datada como del periodo árabe que aparece afectada por un desplazamiento de 55+/-20 cm de la falla AMF. Esto apoya la ocurrencia de eventos con ruptura superficial en época histórica a lo largo de la AMF y refuerza las observaciones obtenidas en estudios paleosísmicos previos. Los escenarios teóricos de eventos de magnitud máxima e intervalos de recurrencia, combinando este evento histórico con los valores de tasa de desplazamiento de la AMF disponibles, considerando el déficit de desplazamiento acumulado, apoyan que la peligrosidad sísmica asociada a eventos de magnitud máxima en esta sección de la AMF puede ser mayor de la considerada hasta ahora.Departamento de Geodinámica, Estratigrafía y Paleontología, Universidad Complutense de Madrid, EspañaInstituto de Geociencias, Consejo Superior de Investigaciones Científicas, EspañaInstituto de Geociencias, Universidad Complutense de Madrid, EspañaDepartamento de Geología y Geoquímica, Universidad Autónoma de Madrid, EspañaInstituto Geológico y Minero de España, EspañaDepartamento de Ingeniería Topográfica y Cartografía, Universidad Politécnica de Madrid, EspañaGrupo RISKNAT, Departament de Dinàmica de la Terra i de l’Oceà, Universitat de Barcelona, EspañaAIA Estudio, Españ

Monitorización geodésica de las zonas de falla de Alhama de Murcia, Palomares y Carrascoy (zona de cizalla de las Béticas Orientales): trabajos en marcha

Reunión Ibérica sobre Fallas Activas y Paleosismología (3ª. 2018. Alicante). - Texto en español con resumen y palabras claves en inglés y españolEl objetivo de este trabajo es llevar a cabo estudios geodésicos en la Zona de Cizalla de las Béticas Orientales, que complementen los estudios paleosísmicos y sismológicos que se están desarrollando en la zona. El objetivo fundamental es determinar la deformación actual que se está produciendo en la zona, lo que permitirá conocer el comportamiento cinemático de los principales segmentos que la forman y su incorporación en la evaluación de la amenaza sísmica de la zona. Para ello, a finales de 2015 se ha establecido una red GPS, con 9 estaciones de campaña y una estación permanente, que complementa las redes existentes, que cubre las zonas de las fallas de Alhama de Murcia, Palomares y Carrascoy y en la que se han realizado dos campañas de observación. En el presente trabajo se presentan el estado actual de la monitorización geodésica, así como algunos resultados preliminares. = The objective of this work is to carry out geodetic studies in the Eastern Betics Shear Zone, which complements the paleoseismic and seismological studies that are being developed in the area. The main objective is to determine the current deformation that is taking place in the area, which will allow to know the kinematic behaviour of the main faults and its constituent segment, and their consequent incorporation into the seismic hazard assessment. For this, at the end of 2015 a GPS network was established, with 9 campaign stations and 1 continuous GPS station, which complements the existing networks, covering the fault zones of Alhama de Murcia, Palomares and Carrascoy and in which two observation campaigns have been carried out. In this paper we present the current state of geodetic monitoring, as well as some preliminary results.Departamento de Ingeniería Topográfica y Cartografía, Universidad Politécnica de Madrid, EspañaDepartamento de Geodinámica, Universidad Complutense de Madrid, EspañaInstituto Geológico y Minero de España, EspañaGrupo RISKNAT, Departament de Dinàmica de la Terra i de l’Oceà, Universitat de Barcelona, EspañaÁrea de Geodesia, Área de Geodesia. Instituto Geográfico Nacional, Españ