Neoteetonics of the eastern border of the Madrid basin

[Abstract] An analysis ofthe neotectonic activity and the current stress state of the eastern border of Madrid Basin has been carried ont using structural-methods (fault population analysis), as well as seismological methods. Two stress tensors have been established: - Tensor 1: with a N1500E shortening trend, characterized mainly by strikeslip faults. This tensor corresponds to the «Guadarrama» stress field (Capote et al., 1990), wihch causes the Central System structure; dated middle Aragonian -lower Pleistocene in the eastern border ofMadrid Basin (Muñoz Martín, 1993). - Tensor 2: dated post-Iower Pleistocene, with a N150° E extension trend, characterized basically by normal faults. Actual stress tensor deduced focal mechanisms by the seismological method is compatible with the paleostress field deduced for the middle-Iower Pleistocene (tensor 2)

Seismogenic zoning based on the geothermal gradient, strenght and depth of the fragile-ductile transition in the upper crust. Methodological approach for seismic hazard calculations in southeast Spain

In this work we present a methodological approach to define seismogenic zones for seismic hazard analysis based on the relationships which can be drawn from the geothermal gradient, total strength of the upper crust and the depth of the fragile-ductile transition, and their relation with the mean focal depth and a parameter hereby defined: Seismic Density Index (number of events per km3 x 1000). A revision of the deep geophysical data available in SE Spain has led to the definition of 6 distinctive crustal blocks. Two main types of crustal blocks are identified: hot-and-weak and cold-and-strong. Hot-and-weak blocks show consistently higher geothermal gradients, lower strengths and shallower fragile-ductile depths than coldand- strong blocks. Furthermore hot-and-weak blocks show higher seismic density indexes and shallower mean focal depths. However, two blocks biased from this relationship and so are called anomalous. According to these results four seismogenic zones can be defined in SE Spain. The a and b parameters of the Gutenberg-Richter law of each zone are consistent with the thermal and strength properties of the blocks. Zones based on the hot-and-weak blocks show higher a and b values than the cold-and-strong ones, while the anomalous blocks show values in between these extreme

Seismic effects in archaeological sites: Archaeoseismological cataloguing and quantification

The analysis of the damage caused by seismic events in archaeological sites provides significant information about ancient and historic earthquakes that can improve seismic hazard analysis. In this paper a methodological analysis to quantify the deformation of structural damage recorded in archaeological sites is proposed. This methodology focuses on the establishment of the seismic/non-seismic origin of the observed damage and consists of three phases: (a) identification and inventory of damage; (b) quantification of deformation; and (c) incorporation of the results to seismic catalogues. The first phase is the inventory and mapping of the damage according with the classification of archaeological effects of earthquakes (EAEs). The second phase is to quantify the deformation of damage by setting different parameters such as the direction of maximum horizontal strain (ey). This analysis is performed at different levels: for each of the recorded EAEs, for all the records of a particular category of EAEs, and finally for the complete archaeological site including all the categories of EAEs. The homogeneity of the results (damage orientation) allows us to establish the seismic origin of deformations. This methodology has been developed in the Roman site of Baelo Claudia (Cádiz, Spain) and has been applied to different historical earthquakes in the Iberian Peninsula. To calibrate the method, analyses on oriented damage were carried out immediately after the recent instrumental earthquakes of Lorca 2011 (5.1 Mw, Spain) and Emilia Romagna 2012 (5.9 Mw; Italy).The analysis of the damage caused by seismic events in archaeological sites provides significant information about ancient and historic earthquakes that can improve seismic hazard analysis. In this paper a methodological analysis to quantify the deformation of structural damage recorded in archaeological sites is proposed. This methodology focuses on the establishment of the seismic / non-seismic origin of the observed damage and consists of three phases: (a) identification and inventory of damage; (b) quantification of deformation; and (c) incorporation of the results to seismic catalogues. The first phase is the inventory and mapping of the damage according with the classification of archaeological effects of earthquakes (EAEs). The second phase is to quantify the deformation of damage by setting different parameters such as the direction of maximum horizontal strain (ey). This analysis is performed at different levels: for each of the recorded EAEs, for all the records of a particular category of EAEs, and finally for the complete archaeological site including all the categories of EAEs. The homogeneity of the results (damage orientation) allows us to establish the seismic origin of deformations. This methodology has been developed in the Roman site of Baelo Claudia (Cádiz, Spain) and has been applied to different historical earthquakes in the Iberian Peninsula. To calibrate the method, analyses on oriented damage were carried out immediately after the recent instrumental earthquakes of Lorca 2011 (5.1 Mw, Spain) and Emilia Romagna 2012 (5.9 Mw; Italy).Este trabajo ha sido financiado por los proyectos CGL2015-67169-P (QTECTSPAIN, USAL) y CATESI-07 (IGME). Es una contribución al INQUA TERPRO Project 1299 y a los grupos de trabajo QTECT-AEQUA y GQMAEQU

Pulverized quartz clasts in gouge of the Alhama de Murcia fault (Spain): evidence for coseismic clast pulverization in a matrix deformed by frictional sliding

The fault gouge of the Alhama de Murcia fault (southeast Spain) shows a texture that resembles a mylonite, including a prominent foliation, S-C fabric, and isoclinal folds. It also embeds a large number of isolated pulverized quartz clasts (PQCs). Structural analysis indicates that the gouge fabric was mainly developed by slow frictional sliding along phyllosili- cate-lined Riedel shear bands during continued shearing. In contrast, the PQCs show tensile fracture network features that are typically reported in seismically pulverized rocks found along seismogenic faults. This suggests that quartz-clast pulverization was due to a transient dilatational mechanism rather than shearing. We propose that the PQCs are the result of a rapid confined stress drop related to transient tensile stresses during coseismic ruptures that interrupt creep faulting along the gouge zone. The present study suggests that there is probably a large amount of evidence for paleoseismicity in fault rocks that is currently overlookedThis research was supported by the Spanish Ministry of Economy and Competitiveness under the INTERGEO (CGL2013–47412-C2–1-P) and QUAKESTEP (CGL2017–83931-C3–1-P) project

Alpine structure and evolution of central Spain

Dirección General de Investigación Científica y Técnica; PB91-039

Paleogeografía sísmica de zonas costeras en la Península Ibérica: su impacto en el análisis de terremotos antiguos e históricos en España

This paper presents three examples of ancient earthquakes occurring in coastal areas of the S and SE of the Iberian Peninsula (218 BC, AD 40-60 and AD 1048) with the aim of illustrating the use of geological and archaeological data in their macroseismic characterization. Historical information for ancient earthquakes that occurred in Spain prior to the 10th century is scarce or non-existent. This paper shows that the current state of knowledge on palaeoseismology and archaeoseismology on these ancient events clearly exceeds the existing historical information allowing the increase of macroseismic information points by using the ESI-07 scale (Environmental Seismic Intensity). Consequently, the geologic analyses of ancient earthquakes contribute to their understanding and parametric evaluations, and improve further advances in seismic hazard assessments. The most significant issue outlined in the present paper is the analysis of the ancient palaeogeography of the affected areas. The studied examples analysed were located in open estuarine areas that have been filled by fluvial sediments or anthropogenic fills over time. The effects of the 218 BC earthquake-tsunami event in the Gulf of Cadiz are analysed in estuarine areas, and especially in the ancient Roman Lagus Ligustinus (Guadalquivir Depression marshes); the effects of the earthquake in AD 40-60 is analysed in the old Roman city of Baelo Claudia located in the Bolonia Bay (Strait of Gibraltar); and the effects of the earthquake of AD 1048on the ancient Sinus Ilicitanus (Bajo Segura Depression) during Muslim times. Descriptions from Roman and Arabic geographers are cross-checked with existing palaeogeographic models based on geological data. This type of analysis results in ancient macroseismic scenarios for the interpretation of theoretical distributions of intensities and environmental effects supporting the concept of “seismic palaeogeography” proposed in this paperEl presente trabajo recoge tres ejemplos de terremotos antiguos (218 AC, 40-60 AD y 1048 AD) ocurridos en zonas litorales del S y SO de la Península Ibérica con la intención de ilustrar el uso de datos geológicos y ar¬queológicos en la caracterización macrosísmica de los mismos. En la mayor parte de los sísmos ocurridos con anterioridad al siglo X d.C. la información documental histórica que se posee es muy escasa o inexistente. El presente trabajo muestra que el actual estado de conocimiento en paleosismología y arqueosismologia sobre este tipo de terremotos sobrepasa con creces la información documental histórica, permitiendo la multiplica¬ción de los puntos de información macrosísmica mediante el uso de la escala ESI-07 (Environmental Seismic Intensity). Consecuentemente, el análisis geológico de los terremotos antiguos mejora su conocimiento y análisis paramétrico, permitiendo avanzar la evaluación de la peligrosidad sísmica de las zonas afectadas. El aspecto que se pone de especial relieve en este trabajo es el análisis de la paleogeografía existente en la antigüedad, ya que todas las zonas (afectadas) analizadas en este trabajo corresponden a zonas estuarinas abiertas que se han ido rellenado por aportes fluviales o de forma artificial con el tiempo. Se analizan los efectos del terremoto de 218 AC en las zonas estuarinas del Golfo de Cádiz y muy especialmente en el antiguo Lacus Ligustinus (marismas del Guadalquivir) durante época romana; los efectos del terremoto de 40-60 AD en la antigua Bahía de Baelo Claudia (Estrecho de Gibraltar); y los efectos del terremoto de 1048 AD en el antiguo Sinus ilicitanus (Depresión del Bajo Segura) durante época musulmana. Se han cotejado descripciones de geógrafos romanos y árabes con modelos basados en datos geológicos. Este tipo de análisis ha permitido generar antiguos escenarios macrosísmicos basados en la paleogeografía y reinterpretar las distribuciones teóricas de intensidades y los efectos ambientales de los terremotos estudiados que es a lo que se refiere el concepto de “paleogeografía sísmica” propuesto en este trabajoThis work has been funded by the Spanish-FEDER research projects CGL2012-37281 C02.01 (QTECTBETICA-USAL), CGL2012-33430 (CSIC) and CGL2013-42847-R (UNED

Criterios geomorfológicos sobre actividad tectónica reciente a lo largo de la Costa Recta, Isla Decepción (Antártida Occidental)

Several active tectonic evidences are observed along Costa Recta, located eastward of Deception Island (western Antarctica): marine terraces and fluvial streams cutting a relict glacier. The height of both landforms decrease southward from Macaroni Point, appointing to a tilt movement across a fault plane. Fault planes were measured at Macaroni Point and Baily Head, with a main NNWSSE orientation, similar to the Costa Recta strike. From several scales o f measure, the orientation of the beach was established in two principal segments: N168QE, and N173QE. On the other hand, the beach and glacier dynamics and sedimentary deposits were studied. According to the morpho-tectonic analysis, we conclude that the Costa Recta beach is a retreat scarp of a submarine fault oriented NNW-SSE and located in the Bransfield Strait, although a geophysical study o f the marine bottom is needed to map the fault trace in an accurate way

Speleoseismology and palaeoseismicity of Benis Cave (Murcia, SE Spain): coseismic effects of the 1999 Mula earthquake (mb 4.8)

This work describes the coseismic ceiling block collapse within Benis Cave (−213 m; Murcia, SE Spain), associated with the 1999 Mula earthquake (mb=4.8, MSK VII). The collapse occurred at −156 m into the Earthquake Hall, and as a consequence one small gallery became blind. We studied the geology, topography and active tectonic structures relevant to the cave. In addition, we carried out a seismotectonic analysis of the focal mechanism solutions, and also a fault population analysis on slickensides measured in fault planes in the cave. The stress and strain regime is interpreted as being congruent with the palaeoseismic evidence, and agrees with the fault kinematics established for cave galleries developed within fault planes and growth anomalies of coral flowstone. Our analysis suggests that one active segment (NNE–SSW) determined the morphology and topography of the Benis Cave, where strong to moderate palaeoearthquakes (6≤M≤7) took place. As a consequence of this intense seismic activity a small gallery collapsed. A new palaeoseismic structure, or seismothem, has been recognized, namely the effect of palaeoearthquakes affecting the pattern of development of the spatial coral flowstone distribution located at the bottom of the cave

Present day kynematic model of the Caribbean Plate in the boundary with the North American and Cocos plates

Este trabajo propone un modelo cinemático en la zona más occidental de la Placa Caribe, en los límites con la Placa Norteamericana y la Placa de Cocos. Para ello se ha realizado un análisis cluster de la sismicidad presente en la zona en función de: 1) su distribución espacial y 2) de la dirección de máximo acortamiento horizontal (ey), obtenidas del análisis de las construcciones de sus mecanismos focales mediante métodos de análisis poblacional de fallas. En total, se han considerado 57 de los 488 sismos con construcción del mecanismo focal situados en la zona. Los resultados obtenidos, tanto de los tensores, como de las trayectorias de deformación sugieren un modelo caracterizado por la rotación de ey en los límites de esta placa con la Placa Norteamérica y en la zona del Arco Volcánico Centroamericano. Esta rotación es congruente con un movimiento lateral hacia el ESE del área más occidental de la Placa Caribe, produciendo una extensión asociada a este movimiento en la zona central del Bloque de Chortis. Este modelo corrobora la existencia de un bloque tectónico costero en la Placa Caribe independiente del Bloque de Chortis (Forearc Sliver).This work proposes a present day kinematic tectonic model for the western part of the Caribbean Plate in relationship at its boundary with the North American and Cocos plates. We have performed the following cluster analysis of the instrumental seismicity within the area: 1) the spatial distribution of focal mechanism solutions and 2) the orientation of the maximum horizontal shortening (ey). Both studies come from the analysis of focal mechanisms by using the fault population technique. From the original available 488 earthquakes with focal mechanism (HCMT online database), we have considered 57 of them according to several criteria. Our results show a clockwise rotation of the ey trajectory across the boundary between Caribbean and North American plates and the Central American Volcanic Arc. This rotation agrees with a lateral tectonic movement towards ESE of the Chortis Block (Caribbean Plate). Furthermore, this model corroborates the existence of a coastal tectonic block within the Caribbean Plate that it is independent from the Chortis Block.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Educación y Cienciapu