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

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

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

Cross-joint forking: 3-D geometry (examples from the Ebro basin, Spain)

Forking is the process of fracture bifurcation ¡rito two or more diverging fracture planes. It occurs when a fracture reaches a critical velocity concomitant with its approach to a previous discontinuity. The literature gives a comprehensive 2-D description of forking, and this work presents a 3-D description of these structures. Outcrop observations suggest that the radiant line (line bounding the parent joint and the bifurcated fractures) is curve shaped (like fracture tip while propagation), and the angle between bifurcated fractures remains aproximately the Same all along the vertical dimension of the joint. This geometry results from the influence of both the previous perpendicular joint towards the parent joint forks and the lithologic boundary at top and bottom of the jointed laye

The E-W and NW-Sh trending joint sets in the Central Ebro Basin (Spain). Relationship with the neogene stress field

Thire are three regional joint sets in the central Ebro, basin. The southern part is. dominated by a primary N-S striking joint set and a secondary E-W set. In the nortnern part, the primary joint set strikes NW-SE Detailed outcrop observations where the three sets do coexist suggest that the E-W set is the result of stress perturbation originated by the previous N-S set over the extensionat NE-SW stress field responsible for the development of the NW-SE joints in the northern are

Dipslip: A QuickBasic stress inversion program for analysing sets of faults without slip lineations

A simple computer program is described for estimating palaeostress tensors from orientation data from a set of fault planes. The computation is based on a novel technique that allows the tensor to be estimated in situations where directions of slip on the faults cannot be determined, but where the senses of the dip-slip component of slip on the faults are known. The new technique greatly broadens the scope of palaeostress analysis, permitting the analysis of faults lacking slickenlines but exhibiting offsets of horizontal marker beds

Observaciones sobre las fracturas de las diaclasas plumosas

Many joint surfaces show en échelon arrays of microfractures (F-joints) along one or both fringes of hackle marks. Our field observations indícate that, where both sets are present, they are stepped in oposite senses. So the F-joints can not be used as shear criteria for discontinuities. Good examples of hackle marks with F-joints have been reproduced in the laboratory by submitting silicone putty to tensile tests when these include sorne rotational component. Rotation induces shear in different senses if observed from an external point of view; so it can explain the development of two sets of Riedel fractures showing opposite stepping. In geological conditions, this rotation occurs around the tips of fractures undergoing vertical displacement. Thus, from this model, hackle marks and F-joints could be used for detecting the sense of small dip-slip movements on joint