Search

[ES] En el Macizo de Herbeira, situado en el Complejo varisco de Cabo Ortegal (NO del Macizo Ibérico), forma parte de una lámina de cabalgamiento constituida por rocas ultramáficas que han sufrido una compleja historia de deformación. La falla de Trans Herbeira (FTH), divide el macizo en dos sectores diferentes. El sector oriental está formado mayoritariamente por harzburgitas ricas en anfíbol, mientras que el sector occidental es litológicamente más variado, con una sucesión de harzburgita basal, dunita inferior, piroxenita media y dunita superior. Se han observado mediante microscopio óptico y SEM, microfábricas equigranulares y porfiroclásticas que evidencian la sucesión de diferentes fases de deformación. Con el análisis de la orientación cristalográfica preferente (OCP) del olivino mediante técnicas de difracción de electrones retrodispersados (EBSD), se han observado sistemas de deslizamiento (010)[100] y {0kl}[100], los cuales se activan en condiciones de altas temperaturas (>1000 ºC), por lo que estas fábricas se desarrollaron durante una fase de deformación de alta temperatura DA. La activación de sistemas de deslizamiento en la dirección cristalográfica [001], así como la observación patrones axiales (010), indican un descenso de la temperatura durante la deformación, por lo que estos patrones han sido atribuidos a una fase de deformación posterior D1. Las temperaturas y las tasas de deformación, de las diferentes fases de deformación observadas, se han estimado mediante paleopiezometría del olivino. Durante la deformación DA las temperaturas alcanzaron más de 1.000ºC, el esfuerzo diferencial fue muy bajo (3-6 MPa) y las tasas de deformación oscilaron entre 10-9 y 10-15 s-1, condiciones que son propias del manto astenosférico. Las deformaciones posteriores (D1 y D2) corresponden a fases de deformación litosféricas, con esfuerzos diferenciales moderadamente altos (8-35 MPa) y tasas de deformación más lentas, como es característico de las deformaciones no localizadas en estado sólido en la corteza inferior y el manto litosférico (10-12 -10-19 s-1)., [EN] The Herbeira ultramafic massif is located in the structural upper portions of the Cabo Ortegal Variscan Complex, NW Galicia, which form part of a thrust sheet that shows a complex deformational evolution. An important strike-slip fault, the Trans Herbeira Fault, divides the massif into two different zones. The eastern one is composed of amphibole bearing harzburgites, whilst the western one has a more complete lithological succession: basal harzburgite, lower dunite, medium pyroxenite and upper dunite. Equigranular and porphyroclastic microfabrics are observed in these rocks under optical microscope and SEM, providing evidence of a succession of several tectonic stages. The analysis of olivine CPO was carried out through electron backscattering diffraction techniques (EBSD).As a result the operating slip systems may be inferred. During de high temperature deformation stage DA the active slip systems were (010)[100] and {0kl}[100]. The activation of [001] axis along the slip direction occurred at lower temperatures (D1 tectonic stage). The estimation of tectonic stress and strain rate was performed by palaeopiezometry of olivine. During DA deformation the temperature reached more than 1000ºC, the tectonic stress level was very low (3-6 MPa) and the strain rate oscillated between 10-9 s-1 and 10-15 s-1, in accordance to the expected values at the mantle. Finally, the D1 deformation was developed at lower temperature (less than 1000ºC), moderately high tectonic stress level (8-35 MPa), and low strain rates (10-12 s-1 to 10-19 s-1), more coherent with the lower crust or uppermost mantle.

En la reciente historia sísmica de España, desde el terremoto de 1956 en Albolote (Granada) con once muertos y el de 1969 al SW del Cabo San Vicente con cuatro, el terremoto de Lorca de 11 de mayo de 2011 (magnitud 5.1) ha vuelto a ser especialmente importante por haber ocasionado nueve víctimas mortales. El movimiento sísmico, localizado muy próximo a la ciudad de Lorca, ha afectado directamente a más de 90.000 personas, que han sufrido sus consecuencias al registrarse con una intensidad de grado VII en la escala europea EMS, lo que ha motivado daños notables en las viviendas. El presente informe trata de reflejar las características del terremoto y de su serie de réplicas, recogiendo los trabajos que han desarrollado diferentes equipos de investigación, tanto previos al terremoto como posteriores. El estudio describe los aspectos científicos y técnicos de mayor interés, desde la historia sísmica de la zona hasta el comportamiento de las edificaciones de la ciudad de Lorca. Asimismo, se acompaña de un encuadre geológico de la zona y de las características de la falla de Alhama de Murcia, responsable de la ocurrencia del terremoto. Como consecuencia de los terremotos que hubo la misma zona en el año 2005, precedidos por un apreciable nivel de actividad sísmica en los años 1999 y 2002, la región de Murcia fue objeto del proyecto RISMUR, cofinanciado por el Instituto Geográfico Nacional y en el que participaron los redactores de este informe. Algunos de los aspectos de este proyecto, en concreto los relativos a la peligrosidad sísmica han sido incluidos, incidiendo en los resultados que se obtuvieron en la ciudad de Lorca. El informe va acompañado al final de una serie de conclusiones en relación con cada uno de los temas tratados, resaltando aquellos aspectos que se deberán tener en cuenta en futuros proyectos, a fin de mejorar por un lado el conocimiento de la sismicidad y peligrosidad sísmica y por otro para la adecuación de la normativa sismorresistente.

The Los Llanos Shear Zone bounds the Cabeza Gorda and Zafra units located in the Ossa-Morena Zone (SW Iberian Massif). Within the Cabeza Gorda unit two peridotitic massifs crop out, named Sierra Cabeza Gorda and Cerro Cabrera. The mylonitic rocks consist of metamorphic and peridotitic rocks extensively deformed that exhibit a penetrative foliation. Mylonitic fabrics are characterized by s and d structures and S-C and S-C’ band. Some examples show a crenulation cleavage that points out the existence of at least two deformation stages. Kinematic criteria are widespread, but dextral-reverse movement prevails both in outcrop and thin section. Los Llanos Shear Zone orientation is NW-SE, similar to variscan structures trend in the area, and deforms precambrian and paleozoic rocks. Los Llanos Shear Zone represents a dextral-reverse structure of Variscan age

The Northwest of the Iberian Peninsula is characterised by the absence of Mesozoic sedimentary deposits, the Cenozoic sediments being scarce. Due to that, the chronology of the geological events in the area is difficult to establish. Nevertheless, in the absence of deposits during a certain time span, the thermal history a particular area during that time-elapse could have been recorded in previous materials. Modelling of the apatite fission-track (AFT) data is a powerful tool to infer geological information in this kind of regions. The tectonothermal history observed in the AFT models begins with the intrusion of the late Variscan granitic plutons and their cooling in the upper crustal levels. After this initial event, three main episodes have been identified. The first involves an important heating during the Upper Jurassic and Earlier Cretaceous, which can be related to the evolution of the Atlantic passive margin. The second heating episode can be connected to the beginning of the Europe-Africa collision during the Upper Cretaceous and the Earlier Palaeogene. Finally, a cooling episode is observed during the Paleogene, which can reflect exhumation processes according with the tectonic structures and the development of the present day topography

The Northwest of the Iberian Peninsula is characterised by the absence of Mesozoic sedimentary deposits, the Cenozoic sediments being scarce. Due to that, the chronology of the geological events in the area is difficult to establish. Nevertheless, in the absence of deposits during a certain time span, the thermal history a particular area during that time-elapse could have been recorded in previous materials. Modelling of the apatite fission-track (AFT) data is a powerful tool to infer geological information in this kind of regions. The tectonothermal history observed in the AFT models begins with the intrusion of the late Variscan granitic plutons and their cooling in the upper crustal levels. After this initial event, three main episodes have been identified. The first involves an important heating during the Upper Jurassic and Earlier Cretaceous, which can be related to the evolution of the Atlantic passive margin. The second heating episode can be connected to the beginning of the Europe-Africa collision during the Upper Cretaceous and the Earlier Palaeogene. Finally, a cooling episode is observed during the Paleogene, which can reflect exhumation processes according with the tectonic structures and the development of the present day topography

The Aguablanca stock is located in the NE zone of the Santa Olalla Igneous Complex, in the Ossa-Morena Zone. Paleozoic rocks of the Bodonal-Cala Complex and Santa Olalla tonalites bound this gabbronorite stock. This rock hosts a Ni-Cu-EGP ore deposit. A gravity survey, Bouguer anomaly map production and 3D gravity modelling have been carried out in the area in order to investigate de Aguablanca stock geometry. The residual gravity map exhibits a gravity high related to the gabbronorite of Aguablanca, a denser rock than the surroundings, as well as to the semi-massive sulphides outcrops. As featured in the 3D density model, the Aguablanca stock has a tabular geometry subparallel to its northern limit, deeping to 1850 m. In its upper part the igneous body spreads and adopts a circular shape. The Aguablanca stock emplacement is related to a variscan ductile shear zone

The Aguablanca stock is located in the NE zone of the Santa Olalla Igneous Complex, in the Ossa-Morena Zone. Paleozoic rocks of the Bodonal-Cala Complex and Santa Olalla tonalites bound this gabbronorite stock. This rock hosts a Ni-Cu-EGP ore deposit. A gravity survey, Bouguer anomaly map production and 3D gravity modelling have been carried out in the area in order to investigate de Aguablanca stock geometry. The residual gravity map exhibits a gravity high related to the gabbronorite of Aguablanca, a denser rock than the surroundings, as well as to the semi-massive sulphides outcrops. As featured in the 3D density model, the Aguablanca stock has a tabular geometry subparallel to its northern limit, deeping to 1850 m. In its upper part the igneous body spreads and adopts a circular shape. The Aguablanca stock emplacement is related to a variscan ductile shear zone

This work analyzes the geological source of the Mw 4.8 February 4 2002, Gérgal earthquake. The interpretation of local geological data, the relocation of the aftershocks sequence using a local velocity model, the focal mechanism calculation and the interferometric study of the area using RADAR images give evidences that support a tensional stress source with a rupture plane oriented NW-SE to NNE-SSW

This work analyzes the geological source of the Mw 4.8 February 4 2002, Gérgal earthquake. The interpretation of local geological data, the relocation of the aftershocks sequence using a local velocity model, the focal mechanism calculation and the interferometric study of the area using RADAR images give evidences that support a tensional stress source with a rupture plane oriented NW-SE to NNE-SSW

The illite crystallinity index of Kubler (1C) has been studied to establish the conditions of the last deformation stages in the Santa María de la Alameda shear zone. For this study, it has been used mainly the fine grained fraction of the samples (less than 2 mm) which is concentrated along small brittle fractures and zones of protocataclasitic material. The studied rocks give "illite crystallinity index" values between 0.35 D°2q and 0.25 D°2q, pointing to deformation conditions at temperatures which denotes a retrograde metamorphismo zone belonging to the epizone and anquizone. These results indicate a a rétrogradation condition for the late brittle deformation stage of the Santa Maria de alameda fault, in temperatures range between 255 and 200° C

Principles of fractal geometry have been applied to the description of quartz grain borders and to the assessment of deformation temperature in milonitic rocks at the Santa Maria de la Alameda Ductile Shear Zone (Central System). This shear zone have evolved during late variscan tectonic period in a large temperature range, which goes from regional metamorphic pick conditions (Amphibolite facies) to temperatures lower than for Greenschists facies. Using fractal dimension analysis techniques and the temperature calibration performed by Kruhl y Nega (1996), have been established a temperature sequence, diminishing from around 490°C to 325°C during the simultaneous processes of milonitization and retrogressive metamorphism. These results are in agreement with temperatures obtained from deformation mechanisms in quartz and potassium feldspar showming the validity of fractal geometry method to deformation temperature assessment

The RADAR interferometry (INSAR) is a modern technique that offers the possibility to identify and quantify surface displacements using phase differences from two different RADAR images (Massonnet and Feigl, 1998). The result of an interferometric study applied to the February 1 999 (Mb: 4.8) Mula (Murcia) earthquake is shown in this work. The available seismological data for this earthquake give different focal mechanisms (reverse or strike-slip mechanism) depending on the applied method. The five coseismic interferograms show that the Mula mainshock produced a very small surface deformation, less than expected for a pure reverse and swallow source. This evidence and the surface geological data support a NE-SO strike-slip fault (probably the Crevillente fault) to be the seismogenetic source

The RADAR interferometry (INSAR) is a modern technique that offers the possibility to identify and quantify surface displacements using phase differences from two different RADAR images (Massonnet and Feigl, 1998). The result of an interferometric study applied to the February 1 999 (Mb: 4.8) Mula (Murcia) earthquake is shown in this work. The available seismological data for this earthquake give different focal mechanisms (reverse or strike-slip mechanism) depending on the applied method. The five coseismic interferograms show that the Mula mainshock produced a very small surface deformation, less than expected for a pure reverse and swallow source. This evidence and the surface geological data support a NE-SO strike-slip fault (probably the Crevillente fault) to be the seismogenetic source

Principles of fractal geometry have been applied to the description of quartz grain borders and to the assessment of deformation temperature in milonitic rocks at the Santa Maria de la Alameda Ductile Shear Zone (Central System). This shear zone have evolved during late variscan tectonic period in a large temperature range, which goes from regional metamorphic pick conditions (Amphibolite facies) to temperatures lower than for Greenschists facies. Using fractal dimension analysis techniques and the temperature calibration performed by Kruhl y Nega (1996), have been established a temperature sequence, diminishing from around 490°C to 325°C during the simultaneous processes of milonitization and retrogressive metamorphism. These results are in agreement with temperatures obtained from deformation mechanisms in quartz and potassium feldspar showming the validity of fractal geometry method to deformation temperature assessment

In this work is shown how an active fold (the Sierra de Cartama fault) is marked by the drainage pattern and topography, besides of structural data. The Sierra de Cartama fold is an asymmetric fold with double plunge and determines the shape of an elongated saw in the Western Betic Chains (South of Spain). Watching the drainage patterns, it can be noticed how streams and creeks round the saw. The uplift of the saw raise the valleys steeply, even leaving a hanging valley ("wind gap ") at the western part of the structure. Regarding to these observations, the lateral propagation of the fold seems to be toward the west. The proposed structure implies the existence of a compressive neotectonic activity in the zone. The compressive horizontal direction is N10e-30eW, perpendicular to the fold axis. In this tectonic environment it could be possible to interpret a reverse fault in deep associated with the fold growth

The Santa Maria de Alameda (Madrid) Ductile Shear Zone is a complex mylonitic belt trending east -West and dipping 30°-60° southward. The hanging wall block sinks towards the South-Southeast. Its kinematics is in relation to an extensional tectonic regime with North-south stretching direction. This large structure belongs to the early stages of the Malagon tectonic period, where important faulting and dike emplacement were produced. The shearing process was developed in retrograde metamorphic conditions in a wide range of temperature, which goes from 400° C to 150° C. The age of this deformation is constrained by the variscan regional metamorphic peak and the intrusion of late variscan granitoids (Las Navas del Marques adamellites), being therefore, between early Namurian and Stephanian

The Santa Maria de Alameda (Madrid) Ductile Shear Zone is a complex mylonitic belt trending east -West and dipping 30°-60° southward. The hanging wall block sinks towards the South-Southeast. Its kinematics is in relation to an extensional tectonic regime with North-south stretching direction. This large structure belongs to the early stages of the Malagon tectonic period, where important faulting and dike emplacement were produced. The shearing process was developed in retrograde metamorphic conditions in a wide range of temperature, which goes from 400° C to 150° C. The age of this deformation is constrained by the variscan regional metamorphic peak and the intrusion of late variscan granitoids (Las Navas del Marques adamellites), being therefore, between early Namurian and Stephanian

Signs of recent tectonic activity are found at the Extremadura sector of Alentejo-Plasencia fault. This fault was active during the alpine compressional period as a sinistraI strike-slip fault at the foreland of a collisional zone and presents some activity from the Miocene to the Quaternary. Upper «Raña» deposits of Early Villafranquian age, present an around-2-meter-vertical-displacement at the north border of Alburquerque granitic massif. Close to this point old fluvial terraces of unknown age are folded and faulted, and low terraces (3 m above present river course) are jointed. In the tertiary Cañaveral pull-apart basin , at the Alcantara reservoir border, the fault disrupts a Tagus river fluvial terrace, which lies 80 m above the river course and has a probable Middle Pleistocene age. All these observations imply a vertical displacement which could be related to a slip rate less than 0.007 mm/year. If this fault is compared with other active faults of the Hesperian Massif, such as the Braganga-Manteigas one, it becomes clear that Alentejo-Plasencia fault is less active. There are though paleoseismicity structures associated to the Alentejo-Plasencia fault, such as liquefaction feature

Signs of recent tectonic activity are found at the Extremadura sector of Alentejo-Plasencia fault. This fault was active during the alpine compressional period as a sinistraI strike-slip fault at the foreland of a collisional zone and presents some activity from the Miocene to the Quaternary. Upper «Raña» deposits of Early Villafranquian age, present an around-2-meter-vertical-displacement at the north border of Alburquerque granitic massif. Close to this point old fluvial terraces of unknown age are folded and faulted, and low terraces (3 m above present river course) are jointed. In the tertiary Cañaveral pull-apart basin , at the Alcantara reservoir border, the fault disrupts a Tagus river fluvial terrace, which lies 80 m above the river course and has a probable Middle Pleistocene age. All these observations imply a vertical displacement which could be related to a slip rate less than 0.007 mm/year. If this fault is compared with other active faults of the Hesperian Massif, such as the Braganga-Manteigas one, it becomes clear that Alentejo-Plasencia fault is less active. There are though paleoseismicity structures associated to the Alentejo-Plasencia fault, such as liquefaction feature

Alentejo-Plasencia fault was active during the alpine compressional phases with a sinistral strike-slip movement in two main stages. The fault geometry was straight and no important bendings formed during Paleogene, when the maximum shortening direction was close to N-S or NNE-SSW. During Miocene (Middle Aragonian) and related to the Neocastellana tectonic phase, the Alentejo-Plasencia fault still moved as a sinistraI strike-slip due to a NW-SE compression, but the Extremadura sector of the fault curved and bends formed along the fault at certain points where important lithologic changes were present. Several restraining and releasing bends formed; these latter creating pull-apart basins, some of them filled with continental clastic sediments. Most of the fault displacement (about 3 Km.) seems to be related to the alpine tectonics. The small displacement compared with the fault length is coherent with its location on a co//s/ona/ area foreland

Alentejo-Plasencia fault was active during the alpine compressional phases with a sinistral strike-slip movement in two main stages. The fault geometry was straight and no important bendings formed during Paleogene, when the maximum shortening direction was close to N-S or NNE-SSW. During Miocene (Middle Aragonian) and related to the Neocastellana tectonic phase, the Alentejo-Plasencia fault still moved as a sinistraI strike-slip due to a NW-SE compression, but the Extremadura sector of the fault curved and bends formed along the fault at certain points where important lithologic changes were present. Several restraining and releasing bends formed; these latter creating pull-apart basins, some of them filled with continental clastic sediments. Most of the fault displacement (about 3 Km.) seems to be related to the alpine tectonics. The small displacement compared with the fault length is coherent with its location on a co//s/ona/ area foreland

The Alpine Structure in the Spanish Central System results from three main regional deformation phases (1-Ibérica, 2-Guadarrama, 3-Torrelaguna) with differents shortening directions, 1-N45E, 2-N750E, 3-N160-200E. The Guadarrama phase (2) include thrusting and Torrelaguna phase (3) include neotectonics, La estructura alpina del Sistema Central español es el resultado de tres fases principales regionales de deformación (1- Ibérica, 2- Guadarrama, 3- Torrelaguna), con diferentes direcciones de acortamiento, 1-N45E, 2-N750E, 3-N160-200E. La fase de Guadarrama (2) incluye cabalgamiento, y la fase Torrelaguna (3) incluye neotectónicas.