Lineamientos y su influencia en los modelados del centro de la Cuenca del Ebro

[Resumen] Mediante la combinación de las bandas 2,4 y 7 de una imagen de Landsat 5 se han identificado 5681 lineamientos en el sector central de la cuenca del Ebro, con longitudes hecto a kilométricas. Se agrupan en dos familias principales, NW-SE y WNW-ESE, y dos secundarias, NNW-SSE y NE-SW. Corresponden en su mayoría a fallas normales. Estos lineamientos condicionan parte del modelado cuaternario de la región, influyendo especialmente en procesos kársticos, distribución de la red de drenaje y evolución de vertientes. Esto permite el empleo de estos criterios geomorfológicos como indicadores de la presencia de lineamientos[Abstract] Within the central Ebro basin, 5681 hecto to kilometric lineaments have been mapped by means a Landsat 5 image with a 2, 4, and 7 bands combination. They belong to two main sets trending NW-SE and WNW-ESE, and two secondary sets trending NNW-SSE and NE-SW. Most of them are normal faults. That lineaments determine sorne of the Quaternary Iandscapes in the area, mainly by its influence in karst, drainage network and slope processes. Actually, that control allows to use those geomorphologic criteria as lineament presence indicators

Stress evolution and structural inheritance controlling an intracontinental extensional basin: The central-northern sector of the Neogene Teruel Basin

The Teruel Basin is a NNE-SSW trending intracontinental extensional basin located in central-eastern Iberia. It is asymmetrically bounded to the east by a major fault zone, but intrabasinal faults with diverse orientation (NNE-SSW to NE-SW, E-W, or NW-SE) also appear. Offsets of the successive sedimentary units and of two planation surfaces reveal that tectonic activity initiated at the border faults, while intrabasinal ones mainly developed in a later stage. Fractures on a map scale show a prevailing N-S strike in Neogene synrift rocks, while a dense network made of four main fracture sets (NE-SW, E-W to ESE-WNW, N-S and NNW-SSE), likely inherited from Mesozoic rifting stages, is observed in pre-rift units. The results of palaeostress analyses indicate an overall predominance of s3 directions around E-W, although two stress episodes have been distinguished during the Late Miocene-Pleistocene: (i) triaxial extension with s3 E-W; (ii) almost ‘radial’ extension (s1 vertical, s2 ˜ s3) with a somehow prevailing s3 ENE-WSW. A scenario in which the evolving extensional stress field was able to gradually activate major basement structures with different orientation, inherited from previous tectonic events, is proposed as responsible for the evolution and overall pattern of both the eastern active margin and central parts of the central-northern sector of the Teruel Basin

Geophysical characterization of buried active faults: the Concud Fault (Iberian Chain, NE Spain)

The Concud Fault is a ~14-km-long active fault that extends close to Teruel, a city with about 35,000 inhabitants in the Iberian Range (NE Spain). It shows evidence of recurrent activity during Late Pleistocene time, posing a significant seismic hazard in an area of moderate-to-low tectonic rates. A geophysical survey was carried out along the mapped trace of the southern branch of the Concud Fault to evaluate the geophysical signature from the fault and the location of paleoseismic trenches. The survey identified a lineation of inverse magnetic dipoles at residual and vertical magnetic gradient, a local increase in apparent conductivity, and interruptions of the underground sediment structure along GPR profiles. The origin of these anomalies is due to lateral contrast between both fault blocks and the geophysical signature of Quaternary materials located above and directly south of the fault. The spatial distribution of anomalies was successfully used to locate suitable trench sites and to map non-exposed segments of the fault. The geophysical anomalies are related to the sedimentological characteristics and permeability differences of the deposits and to deformation related to fault activity. The results illustrate the usefulness of geophysics to detect and map non-exposed faults in areas of moderate-to-low tectonic activity where faults are often covered by recent pediments that obscure geological evidence of the most recent earthquakes. The results also highlight the importance of applying multiple geophysical techniques in defining the location of buried faults

An approach to the seismic hazard at Teruel city associated to the Concud fault (NE Spain)

This paper presents the results ofa probabilistic seismic hazard analysis at Teruel city from seismological and geological information. The characteristic earthquake of the Concud fault (M ~ 6.8; recurrence period = 7.3 ±2.7 ka) has a probabilityof occurrence within a 500-yearperiod ranging from 2.3 to 26.1%. Its parameters fit precisely the magnitude-frequency pattern obtained from the historical seismicity of the Teruel and Jiloca grabens. This coherency supports an estimate of the maximum expectable seism within a 500-yearperiod: M = 5.4± 0.3. Empirical correlations indicate a potential intensity at Teruel overI= VII for this earthquake, and minimum peak ground acceleration ap = 0.105 g, higher than thatspecified by earthquake-resistant building regulationsSe presentan los resultados de un análisis probabilistico de peligrosidad sísmica en el entorno de Teruel a partir de la información geológica y sismológica. El terremoto característico de la falla de Concud (M ~ 6,8;periodo de retorno = 7,3 ±2,7 ka) tiene una probabilidad de ocurrencia en un plazo de 500 años de entre 2,3y26,1 %. Sus parámetros se ajustan bien a la extrapolación de la curva frecuencia-magnitud de la sismicidad histórica en el entorno de las fosas de Teruel yJiloca. En consecuencia, se hace una estimación de la magnitud del seísmo esperable en 500 años: M = 5,4± 0,3. Por correlación empírica se atribuye a éste una intensidad potencial en Teruel por encima de I = VII, y una aceleración de pico mínima ap = 0,105 g, superior a la especificada en la Norma Sismorresistent

Facies control on seismites in an alluvial–aeolian system: the Pliocene dunefield of the Teruel half-graben basin (eastern Spain)

The recognition of seismically induced soft-sediment deformation structures (SSDS) in sedimentary successions characterized by different facies, and hence by different rheology, is challenging. This is the case for high porosity and high permeability aeolian facies interbedded with muddy wet interdune deposits and alluvial conglomerates and sandstones. Several types of SSDS have been studied in two exposures of the Upper Pliocene (2.9–2.6 Ma) sediments of a fault-bounded intracontinental aeolian dune field in the Teruel Basin (Iberian Chain, eastern Spain). Among SSDS, load and fluid-escape structures, apart from several animal tracks, have been recognized. Those structures show an irregular distribution through the studied stratigraphic sections, being scarce in homogenous aeolian sands and frequent in water-related facies. A detailed study of the distribution and geometry of SSDS and their relationships with respect to the stratigraphic architecture and facies has allowed a critical discrimination of trigger mechanisms, i.e. biological or physical overloading vs. earthquakes. The seismically induced structures are concentrated into seven deformed beds, showing an uneven lateral distribution and geometry closely controlled by the hosting sedimentary facies and their rheology. These seismites resulted from liquefaction during moderate earthquakes (estimated magnitude from 5.0 to 6.8). The most probable seismogenic source was the Sierra del Pobo normal fault zone, located 2 km to the East. Results show how an appropriate recognition of sedimentary facies is crucial to understand the lateral variability of seismites in sedimentary environments characterized by sharp facies changes

Recent activity and paleoseismicity of an intraplate extensional fault: the Calamocha fault (Jiloca graben, central Iberian Chain)

The Calamocha fault is an 18-km-long, NNW–SSE striking pure normal fault that moves down the northern sector of the Jiloca graben with respect to the Neogene infill of the Calatayud basin (central Iberian Chain). Its structure and kinematics are characterized by means of detailed geological mapping, morphotectonic analysis and data recording at the outcrop scale. The Calamocha fault represents the inversion of a previous contractional fault zone under the recent tensional stress field (WSW–ENE trending σ3 trajectories). The extensional activity started during the Late Pliocene (ca. 3.8 Ma), accumulating a maximum net slip of 190–230 m (long-term slip rate of 0.05–0.06 mm/a). The palaeoseismological study of three artificial exposures near Calamocha town evidenced recurrent slip during the Late Pleistocene, which proves its active character. Analysis of faulted clastic alluvial units, dated by means of optically stimulated luminescence (OSL), reveals at least eight slip events since 145.9 ± 9.1 ka, the last one being younger than 13.8 ± 0.9 ka. Only a few events represent visible accumulated displacement on the main synthetic rupture surfaces; this allows a rough estimate of the short-term slip rate (during the Late Pleistocene) of about 0.1 mm/a, faster than the long-term rate. The Calamocha fault could potentially produce a characteristic earthquake (in the sense of Schwartz and Coppersmith, J Geophys Res 89:5681–5698, 1984) with moment magnitude Mw ≈ 6.7 ± 0.3 (Mw ≈ 6.9 ± 0.3 in a scenario of activation of the whole Calamocha–Daroca fault zone), average coseismic displacement of 0.5–1.3 m and average recurrence period under 15 ka

Nuevas cartografías temáticas del sector norte de la Fosa de Teruel

La Cuenca de Teruel tiene una dirección N-S y es la mayor estructura extensional intracontinental del Mioceno tardío-Cua- ternario ubicada dentro de la Cadena Ibérica centro-oriental. A pesar de esto, su estudio ha sido algo desigual a lo largo de los años, lo que también se refleja en las cartografías existentes de la cuenca. Los mapas geológicos anteriores a escala de cuenca muestran una carencia en el reconocimiento de las principales estructuras de borde e intracuencales (e.g. Godoy et al., 1983a,b). En este trabajo presentamos un nuevo conjunto de mapas temáticos (geológico, estructural, sedimentario y morfotectónico) del sector norte de la cuenca y su implementación en un espacio de trabajo vectorial, lo que permite un aná- lisis “rápido y fácil” de la fracturación, segmentación estructural, salto vs. distancia y evolución del rifting. La fracturación a escala cartográfica muestra una red de fracturas NE-SW, E-W a ESE-WNW, N-S y NNW-SSE en las rocas mesozoicas del pre-rift, mientras que en los materiales neógenos synrift presentan una dirección N-S dominante en el borde de cuenca pero las principales fallas intracuencales tienen una orientación más diversa (NNE-SSW a NE-SW, E-W o NW-SE). La correlación y los desplazamientos verticales de las sucesivas unidades sedimentarias y de varias superficies de aplanamiento erosivo revelan que la deformación se inició en las fallas del margen, mientras que las fallas intracuencales se desarrollaron principalmente en una etapa posterior. The N-S trending Teruel Basin rift is the largest Late Miocene-Quaternary extensional intracontinental structure located within the central-eastern Iberian Chain. Despite this, its study has been somewhat uneven over the years, which is also reflected in the existing maps of the basin. The previous geological maps at a basin-scale do not recognize the main boundary and intrabasinal structures (e.g. Godoy et al., 1983a,b). In this work, we present a new themed map group of the northern sector (geological, structural, sedimentary and morphotectonic) and their implementation in a vectorial workspace, which allows a “quick&easy” analysis of fractures, segmentation structures, throws vs. distance and rifting evolution. Fractures on a map scale show a network of NE-SW, E-W to ESE-WNW, N-S and NNW-SSE fractures in the pre-rift Mesozoic rocks, while Neogene synrift sediments present a dominant N-S strike in the boundary but intrabasinal major faults with diverse orientation (NNE-SSW to NE-SW, E-W, or NW-SE). The correlation and offsets of the successive sedimentary units and seve- ral planation surfaces reveal that tectonic slip initiated at the border faults under an E-W extension, while intrabasinal ones mainly developed in a later stage

Aproximación a la peligrosidad sísmica en la ciudad de Teruel asociada a la falla de Concud (NE España)

Se presentan los resultados de un analisis probabilistico de peligrosidad sismica en el entorno de Teruel a partir de la informacion geologica y sismologica. El terremoto caracteristico de la falla de Concud (M . 6,8; periodo de retorno = 7,3} 2,7 ka) tiene una probabilidad de ocurrencia en un plazo de 500 anos de entre 2,3 y 26,1 %. Sus parametros se ajustan bien a la extrapolacion de la curva frecuencia-magnitud de la sismicidad historica en el entorno de las fosas de Teruel y Jiloca. En consecuencia, se hace una estimacion de la magnitud del seismo esperable en 500 anos: M = 5,4} 0,3. Por correlacion empirica se atribuye a este una intensidad potencial en Teruel por encima de I = VII, y una aceleracion de pico minima ap = 0,105 g, superior a la especificada en la Norma Sismorresistente. This paper presents the results of a probabilistic seismic hazard analysis at Teruel city from seismological and geological information. The characteristic earthquake of the Concud fault (M ˜6.8; recurrence period = 7.3 ± 2.7 ka) has a probability of occurrence within a 500-year period ranging from 2.3 to 26.1%. Its parameters fit precisely the magnitude-frequency pattern obtained from the historical seismicity of the Teruel and Jiloca grabens. This coherency supports an estimate of the maximum expectable seism within a 500-year period: M = 5.4 ± 0.3. Empirical correlations indicate a potential intensity at Teruel over I = VII for this earthquake, and minimum peak ground acceleration ap = 0.105 g, higher than that specified by earthquake-resistant building regulations

Riesgo de subsidencia kárstica en áreas urbanas: el caso de Zaragoza

Parte del monográfico "Riesgos geológicos externos".[EN] This paper deals with the problems generated by karst in gypsum around Zaragoza, the development of alluvial sinkholes and the concomitant risks. Sinkhole geometry depends on the mechanical behaviour of the cover overlying the evaporitic bedrock: non-cohesive soils favour the development of basin and funnel shaped dolines, whereas cohesive covers lead to the development of well-shaped collapses. Surface survey in areas prone to develop dolines is based on aerial photographs, in situ features (such as topographic depressions, stepped ground, anomalous man-made fills, wet-ground vegetation), and location of building pathologies in urban areas. In some cases, the structure and geometry of dolines can be studied in section (road cuts, for instance), where the features of natural fills allow to characterize the evolutionary patterns and sedimentation- subsidence interactions. Through dating of such fills the rate of subsidence can be estimated, and linked to possible episodes of climate variations. Doline evolution through time, either by comparison of aerial photographs taken in different years or by instrumental survey, yields the scenario of a dynamic process with subsidence rates up to 12 cm/year, where cycles of steady subsidence periods and sudden collapse are identified. In the Zaragoza area, the consequences of karst subsidence are outstanding. They dramatically increased from the 70’s, when large portions of the territory, formerly of agricultural use, turned into urban, industrial and service uses. Prevention and hazard management of karstic risks on urban and peri-urban areas must include: 1) early detection of the problem, in surface as well as underground (by means of geophysical surveys), and 2) adaptation of land use to the degree of affection by karst and the potential susceptibility. Geology, geotechnics and engineering have specific roles on risk management strategies by diminishing either the exposition to karst hazard or the vulnerability of man made structures.[ES] Este trabajo analiza, desde múltiples puntos de vista, la problemática del karst en yesos en el entorno de Zaragoza, el desarrollo de dolinas aluviales y los riesgos que éstas conllevan. La morfología de las dolinas depende del comportamiento mecánico de la cobertera situada sobre el sustrato yesífero: en coberteras sin cohesión aparecen morfologías en embudo y en cubeta, producidas por subsidencia continuada, mientras en coberteras con cohesión se producen dolinas en ventana provocadas por colapso brusco. El reconocimiento superficial de las dolinas se basa en la observación de fotografías aéreas, en el análisis visual del terreno (depresiones topográficas, escalones, áreas de vegetación o rellenos antrópicos anómalos) y en la observación y análisis de daños en áreas urbanizadas. También pueden estudiarse la geometría y la estructura interna de las dolinas en secciones del terreno donde éstas hayan quedado expuestas. Así, las características de sus rellenos naturales permiten conocer las pautas y tasas de evolución y las interacciones entre la subsidencia kárstica y los procesos sedimentarios. El estudio de la evolución temporal de las dolinas, a partir de la comparación de fotografías aéreas de distintos años o del seguimiento instrumental de las mismas, ha permitido reconocer que se trata de un proceso dinámico que llega a alcanzar velocidades de hundimiento de 12 cm/año. En dicha evolución es frecuente la ocurrencia cíclica de periodos de subsidencia lenta y eventos de hundimiento brusco. La afección causada por la subsidencia kárstica en Zaragoza es muy significativa. Ésta se incrementó a partir de los años 70 del siglo pasado, cuando buena parte del suelo agrícola que circundaba la ciudad fue destinado a uso urbano, industrial y grandes infraestructuras. La prevención y manejo del riesgo kárstico en áreas urbanas y peri-urbanas debe contemplar: (1) la detección precoz de los fenómenos tanto en superficie como en profundidad (a partir de estudios geofísicos), y (2) la adaptación del uso del suelo a su grado de afección por fenómenos kársticos y a su susceptibilidad potencial a los mismos. La geología, la geotecnia y la ingeniería desempeñan, cada una, un papel específico en la estrategia para reducir el riesgo, bien sea evitando la exposición al peligro o disminuyendo la vulnerabilidad de las construcciones.Peer reviewe

Variation in the joint pattern along the neogene series of the Sierra de Sigena (Huesca): Possible relationships with the stress Field and its deflection

Neotectonic joints in the Ebro basin strike uniformly NNW-SSE, perpendicular or nearperpendicular to the direction of <33 in the moment it developed. Within the Sierra de Sigena there are joints with anomalous strikes. They show a vertical evolution becoming more similar to the regional fracture pattern as higher in the slope they appair. In the middle portion of the slope this set coexists with the regional-striking joints We interpret this joint distribution as a consequence of stress deflection caused by major faults in the basament, which shows possible attenuation upward