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La aplicación de técnicas de sismicidad pasiva y activa ha permitido observar variaciones en la frecuencia fundamental del suelo en una transversal a los estuarios Odiel y Tinto (Huelva). Los valores más bajos (0,27-0,29 Hz) están en el extremo oriental de la transversal, en las proximidades de Mazagón. Los valores más altos (0,83-1,06 Hz) se localizan en el extremo occidental de la transversal, al oeste del Odiel. El “basamento rocoso” (mecánico) es identificado como el techo del Complejo Basal Transgresivo (calizas neógenas). El zócalo paleozoico estará situado 10-20 metros por debajo de dichas calizas. Se interpreta que fallas extensionales NNE-SSO acomodan la extensión de la corteza terrestre durante el Neógeno en relación con el “forebulge” de la Cuenca del Guadalquivir The application of passive and active seismicity techniques has allowed us to observe variations in the fundamental frequency of the soil in a transversal in the estuaries Odiel and Tinto (Huelva). The lowest values (0.27-0.29 Hz) are at the eastern end of the transversal, near Mazagón. The highest values (0.83-1.06 Hz) are located at the western end of the transversal, west of Odiel. The “rocky basement” (mechanical) is identified as the roof of the transgressive basal complex (limestones of Neogene age). The Paleozoic basement will be located 10-20 meters below these limestones. It is interpreted that NNE-SSO extensional faults accommodate the extension of the earth’s crust during the Neogen in relation to the “forebulge” of the Guadalquivir Basin

La cartografía geológica realizada en una zona próxima a Ayamonte (Huelva) ha permitido analizar los rasgos geológicos más significativos de un alto estructural en el extremo oriental de la cuenca del Algarve. Se describe el registro estratigráfico de una transgresión durante el Triásico Superior, asociada a un evento extensional de tipo “rifting” relacionado con el inicio de la apertura del océano Atlántico. También se muestra el estilo geométrico de los sistemas de fallas normales simultáneos con la actividad ígnea del Triásico y las deformaciones posteriores. La reactivación de zonas de falla durante el Plioceno-Cuaternario y la exhumación de la paleocobertera mesozoica es planteada en relación con la tectónica reciente ligada a la evolución de la cuenca del Guadalquivir The geological cartography carried out in an area near Ayamonte (Huelva) allows us to analyze the most significant geological features of a structural high in the eastern end of the Algarve basin. The stratigraphic record of a transgression during the Upper Triassic, associated with a “rifting” event linked to the beginning of the opening of the Atlantic Ocean, is described. The geometric style of the systems of normal faults simultaneous with the igneous activity of the Triassic and the posterior deformations is also shown. The reactivation of the fault zones during the Pliocene-Quaternary and the exhumation of the Mesozoic paleo-cover is proposed in relation to the recent tectonics, linked to the evolution of the Guadalquivir basin

La cartografía geológica realizada en una zona próxima a Ayamonte (Huelva) ha permitido analizar los rasgos geológicos más significativos de un alto estructural en el extremo oriental de la cuenca del Algarve. Se describe el registro estratigráfico de una transgresión durante el Triásico Superior, asociada a un evento extensional de tipo “rifting” relacionado con el inicio de la apertura del océano Atlántico. También se muestra el estilo geométrico de los sistemas de fallas normales simultáneos con la actividad ígnea del Triásico y las deformaciones posteriores. La reactivación de zonas de falla durante el Plioceno-Cuaternario y la exhumación de la paleocobertera mesozoica es planteada en relación con la tectónica reciente ligada a la evolución de la cuenca del Guadalquivir, The geological cartography carried out in an area near Ayamonte (Huelva) allows us to analyze the most significant geological features of a structural high in the eastern end of the Algarve basin. The stratigraphic record of a transgression during the Upper Triassic, associated with a “rifting” event linked to the beginning of the opening of the Atlantic Ocean, is described. The geometric style of the systems of normal faults simultaneous with the igneous activity of the Triassic and the posterior deformations is also shown. The reactivation of the fault zones during the Pliocene-Quaternary and the exhumation of the Mesozoic paleo-cover is proposed in relation to the recent tectonics, linked to the evolution of the Guadalquivir basin

La aplicación de técnicas de sismicidad pasiva y activa ha permitido observar variaciones en la frecuencia fundamental del suelo en una transversal a los estuarios Odiel y Tinto (Huelva). Los valores más bajos (0,27-0,29 Hz) están en el extremo oriental de la transversal, en las proximidades de Mazagón. Los valores más altos (0,83-1,06 Hz) se localizan en el extremo occidental de la transversal, al oeste del Odiel. El “basamento rocoso” (mecánico) es identificado como el techo del Complejo Basal Transgresivo (calizas neógenas). El zócalo paleozoico estará situado 10-20 metros por debajo de dichas calizas. Se interpreta que fallas extensionales NNE-SSO acomodan la extensión de la corteza terrestre durante el Neógeno en relación con el “forebulge” de la Cuenca del Guadalquivir, The application of passive and active seismicity techniques has allowed us to observe variations in the fundamental frequency of the soil in a transversal in the estuaries Odiel and Tinto (Huelva). The lowest values (0.27-0.29 Hz) are at the eastern end of the transversal, near Mazagón. The highest values (0.83-1.06 Hz) are located at the western end of the transversal, west of Odiel. The “rocky basement” (mechanical) is identified as the roof of the transgressive basal complex (limestones of Neogene age). The Paleozoic basement will be located 10-20 meters below these limestones. It is interpreted that NNE-SSO extensional faults accommodate the extension of the earth’s crust during the Neogen in relation to the “forebulge” of the Guadalquivir Basin

En este trabajo, analizamos la actividad tectónica reciente en el entorno de la cuenca del Viar (antepaís bético) mediante herramientas estructurales y geomorfológicas. Nuestros resultados indican que la segmentación del relieve, tanto paralela como perpendicular al límite entre la cuenca de antepaís del Guadalquivir y el antepaís bético, se debe a actividad tectónica reciente, probablemente cuaternaria. El levantamiento de los relieves que bordean la cuenca del Viar parece estar controlado por la presencia de estructuras previas, reactivadas como fallas oblicuas inversas, de orientación NO-SE, en el NE, y fallas oblicuas normales, aproximadamente E-O, en el SO. Por otra parte, el escalón topográfico que asciende el antepaís bético sobre la cuenca de antepaís está relacionado con actividad reciente de fallas de componente normal dominante. Este ascenso relativo parece haber sido anterior a la subsidencia de la cuenca del Viar, ya que en su borde sur no entran los sedimentos neógenos que afloran en la cuenca del Guadalquivir a la misma cota. Las diferentes estructuras que acomodan el rejuvenecimiento del relieve sugieren la superposición de acortamiento, asociado a tectónica Alpina de intraplaca, y de extensión debida a la flexión del “forebulge" We analyze the recent tectonic activity recorded in the Viar catchment (Betics foreland), combining structural and geomorphic tools. Our results indicate that recent, probably Quaternary, tectonic activity is responsible for relief segmentation, both parallel and perpendicular to the limit between the foreland of the Betics and the Guadalquivir foreland basin. Thus, uplift of the Viar catchment boundaries seems to be controlled by the presence of previous structures, reactivated as NW-SE oblique reverse faults at its NE boundary and oblique normal faults, close to E-W orientation, at its SW boundary. Additionally, SW-NE oblique normal faults are associated with the topographic escarpment that separates the Iberian Massif and the Guadalquivir foreland basin. They must have elevated the Iberian Massif before the subsidence of the Viar catchment occurred, given that the Neogene sediments of the Guadalquivir basin do not extend within the southernmost Viar catchment although its floor is at the same altitude as the Neogene outcrops in the northermost Guadalquivir basin. The contrasting kinematics accommodating relief rejuvenation point to the superposition of shortening, probably due to Alpine intraplate deformation, and extension related to forebulge flexion

En este trabajo, analizamos la actividad tectónica reciente en el entorno de la cuenca del Viar (antepaís bético) mediante herramientas estructurales y geomorfológicas. Nuestros resultados indican que la segmentación del relieve, tanto paralela como perpendicular al límite entre la cuenca de antepaís del Guadalquivir y el antepaís bético, se debe a actividad tectónica reciente, probablemente cuaternaria. El levantamiento de los relieves que bordean la cuenca del Viar parece estar controlado por la presencia de estructuras previas, reactivadas como fallas oblicuas inversas, de orientación NO-SE, en el NE, y fallas oblicuas normales, aproximadamente E-O, en el SO. Por otra parte, el escalón topográfico que asciende el antepaís bético sobre la cuenca de antepaís está relacionado con actividad reciente de fallas de componente normal dominante. Este ascenso relativo parece haber sido anterior a la subsidencia de la cuenca del Viar, ya que en su borde sur no entran los sedimentos neógenos que afloran en la cuenca del Guadalquivir a la misma cota. Las diferentes estructuras que acomodan el rejuvenecimiento del relieve sugieren la superposición de acortamiento, asociado a tectónica Alpina de intraplaca, y de extensión debida a la flexión del “forebulge", We analyze the recent tectonic activity recorded in the Viar catchment (Betics foreland), combining structural and geomorphic tools. Our results indicate that recent, probably Quaternary, tectonic activity is responsible for relief segmentation, both parallel and perpendicular to the limit between the foreland of the Betics and the Guadalquivir foreland basin. Thus, uplift of the Viar catchment boundaries seems to be controlled by the presence of previous structures, reactivated as NW-SE oblique reverse faults at its NE boundary and oblique normal faults, close to E-W orientation, at its SW boundary. Additionally, SW-NE oblique normal faults are associated with the topographic escarpment that separates the Iberian Massif and the Guadalquivir foreland basin. They must have elevated the Iberian Massif before the subsidence of the Viar catchment occurred, given that the Neogene sediments of the Guadalquivir basin do not extend within the southernmost Viar catchment although its floor is at the same altitude as the Neogene outcrops in the northermost Guadalquivir basin. The contrasting kinematics accommodating relief rejuvenation point to the superposition of shortening, probably due to Alpine intraplate deformation, and extension related to forebulge flexion

En este trabajo se describe la serie sísmica producida entre septiembre de2017 y febrero de 2018 en México, que incluye un terremoto de Mw=8.2 yotros dos de magnitud superior a 7.0. El estudio detallado de los mecanismosfocales de los eventos analizados, de la distribución espacial de los focos de losterremotos principales y de sus réplicas permite una primera interpretación sis-motectónica. Se sugiere que, en el contexto de la subducción de la placa deCocos bajo la Norteamericana, cerca de la unión triple con la placa Caribe, elslabsubducente estaría sometido en la zona del Golfo de Tehuantepec a unfuerte estiramiento (quizá debido a un proceso de slab roll-backo a una granactividad de la fuerza de slab pull), dando lugar al evento principal. La actividadsísmica producida posteriormente en la placa Norteamericana habría estadodesencadenada por dicho evento principal This work describes the seismic series occurred between September2017 and February 2018 in Mexico, which includes an earthquake ofMw=8.2, and another two of magnitude greater than 7.0. The detailed studyof their focal mechanisms, and the spatial distribution of the mainearthquakes and their aftershocks, allow a seismotectonic interpretation ofthis seismic activity. It is here suggested that, in the general setting of thesubduction of the Cocos Plate under the North America Plate, close to theirtriple junction with the Caribbean Plate, the subducting slab is subjected toa strong stretching below the Tehuantepec Gulf (probably due to a slab rollback process or to a great activity of the slab pull force), which gave rise tothe main event. The subsequent seismic activity that affected the NorthAmerica Plate would have been triggered by that main event

En este trabajo se presentan algunas ideas que pueden aplicarse en clase para que los estudiantes aprendan las técnicas y principios del mapa geológico. Los estudiantes tendrán la oportunidad de conocer el arte de hacer un mapa geológico. Cualquier profesor puede seguir las explicaciones detalladas del texto y con ello hacer pensar a los estudiantes sobre: i) las curvas de nivel en los mapas topográficos, ii) patrones de afloramiento de los contactos geológicos y las reglas de la “V”, iii) espesor real y aparente de los niveles geológicos (estratos / unidades). Las láminas que hemos elaborado, a modo de modelos geológicos 2-D y 3-D dibujados en papel, ayudan a entender mejor el concepto mismo del mapa geológico. Este trabajo presenta un caso práctico que analiza la elaboración del mapa geológico de la ciudad de Huelva y un modelo geológico tridimensional donde se observan estratos subhorizontales., This paper presents a series of techniques that teachers can use in the classroom to familiarise their students with the fundamentals of geological mapping. By following the detailed practical explanations provided in this text, teachers can guide students to think about: i) topographical contour maps, ii) geological outcrop patterns and the V-rule, iii) true and apparent thickness of layers (strata/units). The sheets (2-D and 3-D geological paper models) provided herein offer a better understanding of the concept of geological maps. A practical case study is described that analyses the geological mapping of the city of Huelva, also presenting a 3-D geological model with sub-horizontal strata.

En este trabajo se presentan algunas ideas que pueden aplicarse en clase para que los estudiantes aprendan las técnicas y principios del mapa geológico. Los estudiantes tendrán la oportunidad de conocer el arte de hacer un mapa geológico. Cualquier profesor puede seguir las explicaciones detalladas del texto y con ello hacer pensar a los estudiantes sobre: i) las curvas de nivel en los mapas topográficos, ii) patrones de afloramiento de los contactos geológicos y las reglas de la “V”, iii) espesor real y aparente de los niveles geológicos (estratos / unidades). Las láminas que hemos elaborado, a modo de modelos geológicos 2-D y 3-D dibujados en papel, ayudan a entender mejor el concepto mismo del mapa geológico. Este trabajo presenta un caso práctico que analiza la elaboración del mapa geológico de la ciudad de Huelva y un modelo geológico tridimensional donde se observan estratos subhorizontales. This paper presents a series of techniques that teachers can use in the classroom to familiarise their students with the fundamentals of geological mapping. By following the detailed practical explanations provided in this text, teachers can guide students to think about: i) topographical contour maps, ii) geological outcrop patterns and the V-rule, iii) true and apparent thickness of layers (strata/units). The sheets (2-D and 3-D geological paper models) provided herein offer a better understanding of the concept of geological maps. A practical case study is described that analyses the geological mapping of the city of Huelva, also presenting a 3-D geological model with sub-horizontal strata.

En los “cabezos” de Huelva se han producido importantes fenómenos de inestabilidad de laderas que han tenido en ocasiones consecuencias catastróficas. Los “cabezos” son elevaciones topográficas, desarrolladas sobre las Formaciones sedimentarias “Arenas de Huelva” y “Arenas de Bonares”. Estos materiales areno-limosos, cuyas propiedades geotécnicas han sido caracterizadas en este trabajo, están siendo afectados por la erosión hídrica superficial y los movimientos en masa, especialmente, más activos en épocas de importantes lluvias. Se presenta un estudio de los deslizamientos que han afectado a los “cabezos” próximos a la Plaza de Toros de Huelva, desde 1984 hasta 2010. Para este periodo se han identificado los momentos de intensificación de los procesos de erosión y los deslizamientos coincidiendo con un incremento de la precipitación media anual entre un 44% y un 85%. Por otra parte, los deslizamientos han sucedido cuando la lluvia acumulada supera los 300 mm y la intensidad diaria ha sido igual o mayor a 40 mm. El análisis retrospectivo de los deslizamientos estudiados ha permitido determinar resistencias de pico con valores de φ’=17º±5º y resistencias residuales con φ’=6º±3º. Estos datos pueden servir de punto de partida para la recomendación y diseño de medidas preventivas, y/o en su caso, correctoras de estabilidad., In the “cabezos” (hills) of Huelva there have been important phenomena of instability which sometimes originated disastrous consequences. These represent topographic elevations developed mainly in the geological formations “Huelva Sands“ and “Bonares Sands“ being formed by sandy-silty material. We have studied and characterized the geotechnical properties of the levels of sands in different slopes, near Huelva’s bullring. The slopes are being affected by water superficial erosion and mass movements, which are very active in times of significant rainfall. This study is based on detailed geometric of landslides analysis and related rainfall patterns, for the time period from 1984 to 2010. In this period have been recognized the moments more actives of erosion and landslides, which coincide with increase between 44% and 85% in annual mean rainfall. On the other hand, landsliding is seen to be related to a period preparatory of 1-2 months with values of cumulative rainfall more than 300 mm and a daily intensity upper than 40 mm. Back analyses of landslides provide a peak and residual friction angles (φ’) of 17º±5º and 6º±3º, respectively. This work can serve as a starting point for the recommendation and design of preventive actions, or where appropriate, corrective of stability.

En fallas que siguen el modelo de deslizamiento, la utilización de las técnicas de análisis de poblaciones de fallas para obtener la orientación y magnitud de los ejes principales del esfuerzo a partir de sistemas incompletos (menos de cuatro familias), suele proporcionar orientaciones inclinadas para dichos ejes. Se puede demostrar que, en sistemas completos (es decir, con cuatro familias de fallas), las variaciones en el buzamiento de las familias de fallas y en el cabeceo de las estrías no modifican la dirección ni la inmersión del aquí llamado eje invariante del esfuerzo (σ1 para fallas inversas y σ3 para fallas normales). Esta observación ha permitido desarrollar un método empírico para corregir la orientación de los ejes invariantes del esfuerzo en sistemas incompletos de fallas, al que se ha denominado método β-stress, asumiéndose que uno de los ejes principales del esfuerzo es vertical. La técnica consiste en la determinación de la desviación en el ángulo medido en la horizontal (ángulo β) entre la dirección de inmersión del eje invariante inclinado calculado a partir del sistema incompleto, y la posición no desviada del eje que teóricamente debe haber afectado al sistema de fallas, y que habríamos medido en caso de haber dispuesto de las cuatro familias del sistema. El método se ha aplicado con éxito para la corrección de los ejes del esfuerzo obtenidos tras el análisis de fallas de edades miocenas y plioceno-cuaternarias localizadas en el área emergida del Golfo de Cádiz., The techniques of fault-slip stress inversion can be used on faults that follow the slip model (with four fault sets arranged in a system with orthorhombic symmetry) to determine the position and magnitude of the principal stress axes. In incomplete fault systems (less than four sets) the calculated stress axes are commonly inclined. It is shown here that, in complete fault systems, variations in fault dip and striae pitch do not modify the trend or the plunge of the here-called invariant stress axis (σ1 for reverse faults and σ3 for normal faults). This feature allowed us to propose a new empirical technique, the β-stress method, to correct the position of the invariant stress axes in incomplete fault systems. One of the assumptions of the method is that one of the principal stress axis is vertical. The β-stress method yields the horizontal deviation angle, β, between the trend of an inclined invariant axis determined from an incomplete fault system, and the theoretical, correct attitude of this axis, which would have been measured if the four sets of the complete system were available at the studied outcrop. The method has been successfully applied to correct the orientation of the principal stress axes obtained after stress inversion of Miocene and Pliocene-Quaternary faults located in the Gulf of Cádiz.

En fallas que siguen el modelo de deslizamiento, la utilización de las técnicas de análisis de poblaciones de fallas para obtener la orientación y magnitud de los ejes principales del esfuerzo a partir de sistemas incompletos (menos de cuatro familias), suele proporcionar orientaciones inclinadas para dichos ejes. Se puede demostrar que, en sistemas completos (es decir, con cuatro familias de fallas), las variaciones en el buzamiento de las familias de fallas y en el cabeceo de las estrías no modifican la dirección ni la inmersión del aquí llamado eje invariante del esfuerzo (σ1 para fallas inversas y σ3 para fallas normales). Esta observación ha permitido desarrollar un método empírico para corregir la orientación de los ejes invariantes del esfuerzo en sistemas incompletos de fallas, al que se ha denominado método β-stress, asumiéndose que uno de los ejes principales del esfuerzo es vertical. La técnica consiste en la determinación de la desviación en el ángulo medido en la horizontal (ángulo β) entre la dirección de inmersión del eje invariante inclinado calculado a partir del sistema incompleto, y la posición no desviada del eje que teóricamente debe haber afectado al sistema de fallas, y que habríamos medido en caso de haber dispuesto de las cuatro familias del sistema. El método se ha aplicado con éxito para la corrección de los ejes del esfuerzo obtenidos tras el análisis de fallas de edades miocenas y plioceno-cuaternarias localizadas en el área emergida del Golfo de Cádiz. The techniques of fault-slip stress inversion can be used on faults that follow the slip model (with four fault sets arranged in a system with orthorhombic symmetry) to determine the position and magnitude of the principal stress axes. In incomplete fault systems (less than four sets) the calculated stress axes are commonly inclined. It is shown here that, in complete fault systems, variations in fault dip and striae pitch do not modify the trend or the plunge of the here-called invariant stress axis (σ1 for reverse faults and σ3 for normal faults). This feature allowed us to propose a new empirical technique, the β-stress method, to correct the position of the invariant stress axes in incomplete fault systems. One of the assumptions of the method is that one of the principal stress axis is vertical. The β-stress method yields the horizontal deviation angle, β, between the trend of an inclined invariant axis determined from an incomplete fault system, and the theoretical, correct attitude of this axis, which would have been measured if the four sets of the complete system were available at the studied outcrop. The method has been successfully applied to correct the orientation of the principal stress axes obtained after stress inversion of Miocene and Pliocene-Quaternary faults located in the Gulf of Cádiz.

Este trabajo describe la terminación oriental de la Zona de Fractura Azores- Gibraltar y se propone, basándonos de datos sísmicos, la existencia de una zona de “restraining bend” formada por fallas inversas de dirección NESO y fallas E-O de desplazamiento en dirección. A partir de una revisión de datos geológicos y geofísicos, incluyendo perfiles sísmicos de reflexión y el registro instrumental de la sismicidad para el periodo 2004-2010, hemos podido definir el citado “restraining bend” como una importante zona transpresiva dextrorsa, con una forma romboidal -en planta-, ligada al límite actual entre las placas Africana y Euroasiática, y comprendida entre la Falla Gloria y el Arco de Gibraltar. La cinemática de las placas en dicho límite es congruente con la orientación del patrón estimado para las trayectorias de SH: NNO-SSE, This work describes the eastern part of the Azores-Gibraltar Fracture Zone and it proposes, mainly based on seismic data, the activity of a restraining bend consisting of NE-SW reverse faults and E-W-oriented strikeslip faults. A review of geological and geophysical data, including seismic reflection profiles and the use of catalogs of instrumental seismicity for the period 2004-2010, allow to define this restraining bend as a huge dextral transpression zone, with a rhomboidal shape in plan view, outlining the present- day boundary between the African and Eurasian plates at the segment comprised between the Gloria Fault and the Gibraltar Arc. The plate kinematics at this boundary is consistent with the estimated pattern of NNW-SSEtrending SH trajectories

Este trabajo describe la terminación oriental de la Zona de Fractura Azores- Gibraltar y se propone, basándonos de datos sísmicos, la existencia de una zona de “restraining bend” formada por fallas inversas de dirección NESO y fallas E-O de desplazamiento en dirección. A partir de una revisión de datos geológicos y geofísicos, incluyendo perfiles sísmicos de reflexión y el registro instrumental de la sismicidad para el periodo 2004-2010, hemos podido definir el citado “restraining bend” como una importante zona transpresiva dextrorsa, con una forma romboidal -en planta-, ligada al límite actual entre las placas Africana y Euroasiática, y comprendida entre la Falla Gloria y el Arco de Gibraltar. La cinemática de las placas en dicho límite es congruente con la orientación del patrón estimado para las trayectorias de SH: NNO-SSE This work describes the eastern part of the Azores-Gibraltar Fracture Zone and it proposes, mainly based on seismic data, the activity of a restraining bend consisting of NE-SW reverse faults and E-W-oriented strikeslip faults. A review of geological and geophysical data, including seismic reflection profiles and the use of catalogs of instrumental seismicity for the period 2004-2010, allow to define this restraining bend as a huge dextral transpression zone, with a rhomboidal shape in plan view, outlining the present- day boundary between the African and Eurasian plates at the segment comprised between the Gloria Fault and the Gibraltar Arc. The plate kinematics at this boundary is consistent with the estimated pattern of NNW-SSEtrending SH trajectories

Detailed geological study of the western part of a new road leading to Lanjarón (Betic Cordillera) has revealed the existence ofnatural instabilities in metapelitic rock masses ofthe Alpurrides Units. We have analysed the stability of the future slopes in the Cerro de la Escolta based on detailed geological mapping and measurement of structural data and mechanical discontinuities

Deformation structures below the basal plane of gravitational slides can provide useful information about the state of stress undergone by rocks prior to the sliding process and about the triggering forces acting at each particular sliding event. In the present work we conducted a structural analysis of the rocks below the surface of the gravitational slide of Tazo (La Gomera, Canary Islands) and determined the epigenetic processes involved in the filling of the amphitheatre. We also inferred the possible triggering phenomena related to the Tazo landslide. The rocks located below the surface of the gravitational slide of Tazo -i.e., the basaltic lava flows, sills and dikes of the Lower Old Edifice and the submarine volcanic rocks, gabbros, pyroxenites and dikes of the Basal Complex of La Gomera- are strongly deformed close to this sliding surface. The lava flows and dikes of the Lower Old Edifice are folded, with fault breccias and gouges, and locally foliated, defining the sliding surface. The dikes of the Basal Complex are also folded, and the gabbros and pyroxenites are affected by a large number of small faults. In the Basal Complex, the sliding surface is defined by a foliated granular gouge. In the damage zone, the Basal Complex rocks show an incipient fracture cleavage. The sliding amphitheatre has been filled by the debris avalanche or cohesive debris flow generated within the slide, as well as by later debris flows, hyperconcentrated flows, sheet flows, and by interspersed lava flows from the Upper Old Edifice. We suggest here that the collapse of the north-western flank of the Lower Old Edifice at Tazo could in part have been triggered by continuous magma injection, associated with the emplacement of dikes in a rift zone with an ENE-WSW direction, enhanced by the mechanical weakness of the Basal Complex unit, which was affected by hydrothermal metamorphism under greenschist facies conditions and by the displacement along the Montana de Alcala and Guillama normal faults, which are deeply entrenched in the altered rocks of the Basal Complex

Detailed geological study of the western part of a new road leading to Lanjarón (Betic Cordillera) has revealed the existence ofnatural instabilities in metapelitic rock masses ofthe Alpurrides Units. We have analysed the stability of the future slopes in the Cerro de la Escolta based on detailed geological mapping and measurement of structural data and mechanical discontinuities

Geological map of Virgen de la Peña rock massif has established that there are three sets of geological discontinuities in the rock mass: a) stratification set strikes NW-SE and dips more 70º NE; b) faults set strikes NE-SW and has gently dips and c) joints set strike NE-SW showing steeply dips. Cubical or tabulate blocks are formed by three intersecting discontinuity sets. The analysis of stability of rock massif illustrates the mechanics of failure involve the block toppling and sliding. The index Rock Mass Rating (RMR, Bieniawski, 1989) is obtained

Geological map of Virgen de la Peña rock massif has established that there are three sets of geological discontinuities in the rock mass: a) stratification set strikes NW-SE and dips more 70º NE; b) faults set strikes NE-SW and has gently dips and c) joints set strike NE-SW showing steeply dips. Cubical or tabulate blocks are formed by three intersecting discontinuity sets. The analysis of stability of rock massif illustrates the mechanics of failure involve the block toppling and sliding. The index Rock Mass Rating (RMR, Bieniawski, 1989) is obtained

This work deals with the analysis of the seismicity and tectonic evolution of the eastern end of the Azores – Gibraltar Fracture Zone. The location of the main seismogenetic areas in this region is related to the complex geometry of the boundary between the Iberian and African lithospheric plates. To the west of the San Vicente Cape the seismicity can be related to a local compression at the Gorringe Bank. A detailed seismotectonic analysis allows the geological interpretation of the position of the hypocenter for the 12th February 2007 earthquake. It had Mw 6.0 and was placed on a fault having a NNE-SSW strike and a high dip to NW. The fault shows an oblique displacement (sinistral) and locates in the margin of the Horseshoe abyssal basin. Displacement along this fault is here tentatively related to complex deformation in the outer swell of an incipient downgoing plate. This can be the first indication of the beginning of subduction of the northern part of the African plate under the continental margin of Iberia. On the other hand, an analysis of the location of earthquakes having Mw >6.0 generated to the SW of the San Vicente Cape and the estimated isoseismal map has been made. It can be noted the importance of the uppermost crustal materials on the seismic intensity measurement. Sea waves resulting from these earthquakes and measured in the littoral of the Huelva province have an average velocity of propagation of approximately 600 km/h

Three major tectonic domains have been established in the South Portuguese Zone on the basis of cartographic, stratigraphic, lithologic, structural and metamorphic criteria. They are from north to south and from the upper to lowest tectonic position: Northern Domain, Central Domain or Iberian Pyrite Belt and Southern Domain

Three major tectonic domains have been established in the South Portuguese Zone on the basis of cartographic, stratigraphic, lithologic, structural and metamorphic criteria. They are from north to south and from the upper to lowest tectonic position: Northern Domain, Central Domain or Iberian Pyrite Belt and Southern Domain

This paper shows the preliminary results of a laboratory geotechnical test for the identification and determination of consolidation properties of the soils of Huelva. The fine-grained soils (Arcillas de Gibraleón, Arenas de Huelva and Arenas de Bonares units) have a high consistency. These are over-consolidated soils which have few compressibilities. The Arcillas de Gibraleón Unit presents expansive clay minerals

This paper shows the preliminary results of a laboratory geotechnical test for the identification and determination of consolidation properties of the soils of Huelva. The fine-grained soils (Arcillas de Gibraleón, Arenas de Huelva and Arenas de Bonares units) have a high consistency. These are over-consolidated soils which have few compressibilities. The Arcillas de Gibraleón Unit presents expansive clay minerals

High volumes of diabase dykes outcrop in the Eastern part of the South Portuguese Zone, which crosscutting the subvolcanic and plutonic rocks of the Seville Range batholith (SRB), and they are covered by permian deposits of the Viar Basin. Geochemically, the diabases were originated in a tectonic setting similar to basic rocks of the SRB, therefore both have been derived from the same matelic source in a tectonic setting of active margin

High volumes of diabase dykes outcrop in the Eastern part of the South Portuguese Zone, which crosscutting the subvolcanic and plutonic rocks of the Seville Range batholith (SRB), and they are covered by permian deposits of the Viar Basin. Geochemically, the diabases were originated in a tectonic setting similar to basic rocks of the SRB, therefore both have been derived from the same matelic source in a tectonic setting of active margin

Folds, reverse faults and thrusts in the South Portuguese Zone (SW Iberia) have been classically related with the progressive deformation of the Variscan thrust -fold belt. All structures verge toward South and Southwest. The style of folds in multilayers is analysed in this work. Ductile, brittle-ductile and brittle shear zones cut across the tight folds wisch exibit a WNW-ESE trend. The dip of axial surfaces varies from moderately inclined to upright. Detailed research in the Valverde del Camino anticlinal has revealed the existence of dome-basin patterns of folds related with the thrusts. The regional structures such as the Puebla de Guzmán and Valverde del Camino anticlinorium are associated with the geometry of thrusts

Folds, reverse faults and thrusts in the South Portuguese Zone (SW Iberia) have been classically related with the progressive deformation of the Variscan thrust -fold belt. All structures verge toward South and Southwest. The style of folds in multilayers is analysed in this work. Ductile, brittle-ductile and brittle shear zones cut across the tight folds wisch exibit a WNW-ESE trend. The dip of axial surfaces varies from moderately inclined to upright. Detailed research in the Valverde del Camino anticlinal has revealed the existence of dome-basin patterns of folds related with the thrusts. The regional structures such as the Puebla de Guzmán and Valverde del Camino anticlinorium are associated with the geometry of thrusts

Graphical and numerical methods of fault slip data inversion have been applied to obtain palaeostress reconstructions in Neogene and Quaternary basins, located in the northwestern part of Gibraltar Arc. The most important brittle structures affecting these sediments are high-angle faults with oblique-slip. Two sets of faults with NW-SE and NE-5W trends have been distinguished. The trend of the major axis of the palaeostress ellipse in the horizontal plane has rotated from E-W in the Upper Miocene to NW-SE in the Pliocene-Quaternary

Graphical and numerical methods of fault slip data inversion have been applied to obtain palaeostress reconstructions in Neogene and Quaternary basins, located in the northwestern part of Gibraltar Arc. The most important brittle structures affecting these sediments are high-angle faults with oblique-slip. Two sets of faults with NW-SE and NE-5W trends have been distinguished. The trend of the major axis of the palaeostress ellipse in the horizontal plane has rotated from E-W in the Upper Miocene to NW-SE in the Pliocene-Quaternary

The Mesozoic outcrops of southwestern Spain show a complex succession of sedimentary and volcanic rocks. Their deposition is related to the first episodes of rifting between Africa and Iberia that took place from the Late Triassic to the Early Jurassic. Subsequent tectonic events generated brittle post-lithification structures, mainly normal faults and joints. The use of inverse methods of fault analysis to evaluate the stress and strain tensors that originated these structures, reveals a first episode of N-S extension, closely followed by an E-W extension. This tectonic evolution, tentatively dated as Early Cretaceous, can be explained in the context of the eastwards movement of the African plate with respect to Iberia along a transtensional, sinistral shear band

The Mesozoic outcrops of southwestern Spain show a complex succession of sedimentary and volcanic rocks. Their deposition is related to the first episodes of rifting between Africa and Iberia that took place from the Late Triassic to the Early Jurassic. Subsequent tectonic events generated brittle post-lithification structures, mainly normal faults and joints. The use of inverse methods of fault analysis to evaluate the stress and strain tensors that originated these structures, reveals a first episode of N-S extension, closely followed by an E-W extension. This tectonic evolution, tentatively dated as Early Cretaceous, can be explained in the context of the eastwards movement of the African plate with respect to Iberia along a transtensional, sinistral shear band