Comparative geometrical study of fault-propagation folds associated with lateral tips of thrusts

This work examines the geometry of two examples of fault-propagation folds related to the lateral termination of thrusts. In spite of their differences in age (Variscan and Alpine) and composition of the involved rocks (metamorphic or sedimentary), the geometry of the resulting folds is quite similar, indicating that are universal the mechanisms responsible for these structure

Seismotectonics related to the Azores – Gibraltar Fracture Zone: Analysis of the February 12th 2007 earthquake, SW Gorringe Bank

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/

Geometry and Cinematics of the Fan Imbricated Thrust System in the Iberian Pyrite Belt (South Portuguese Zone)

The Puebla de Guzmán and Valverde del Camino Anticlines consist of fault-propagation folds linked to a frontal thrust system striking N110ºE. In the Puebla de Guzmán Anticline, the thrust system has a fan imbricated geometry and represents a ~40 km-long and 4-5 km-wide frontal ramp; its internal structure results from the tectonic stacking of thrust sheets with normal stratigraphic polarities. Some thrusts show relay geometries, as for example the Valdecascajos and the Sierra de la Estrella Thrusts. An antiform-sinform system is developed in the intervening thrust sheet. Fault-propagation folds are very conspicuous in the hanging wall of most internal thrusts, where a rather continuous reverse limb is present. Both thrust system and fault-propagation folds, as well as a locally developed crenulation cleavage, were generated in a second tectonic phas

Estudio geométrico comparativo de pliegues asociados a la propagación y terminación lateral de cabalgamientos

This work examines the geometry of two examples of fault-propagation folds related to the lateral termination of thrusts. In spite of their differences in age (Variscan and Alpine) and composition of the involved rocks (metamorphic or sedimentary), the geometry of the resulting folds is quite similar, indicating that are universal the mechanisms responsible for these structures

Analysis of the instabilities types in the Rock Massif of Virgen de la Peña (Huelva, Spain)

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 obtaine

Post-sedimentary structures in the northwestern sector of the Guadalquivir foreland basin (Niebla, Candón, Valverde del Camino), SW Spain

Description of deformational structures in tertiary sediments, which have been interprerted as a result of a fluids migration process, along with the presence of preferential structural directions of fracture planes developed in the substratum. This fracture net could have been recently reactivated, so leading to the development of the described structure