Abstract
This paper presents a synthesis of the neotectonic studies performed in mainland Portugal that address the “recent” (post Piacenzian, ~3 Ma) tectonic evolution of the Portuguese territory as part of the West Iberian continental margin, specifically in regard to regional seismic hazard evaluation. The interaction of the Iberian microplate with the Nubia plate is identified as the source for the regional neotectonic deformations, which occur at relatively low rates in spite of significant historical seismic activity. In this context of low strain rates expressed by the presence of slow slip rate active faults, it is important to acquire paleoseismic data on the major seismogenic structures to characterize the large earthquakes that they generated in the past, because average recurrence intervals are much longer than the time span covered by the regional historical and instrumental period.
Highlights
Este artículo presenta una síntesis sobre los trabajos de neotectónica que se han llevado a cabo en el Portugal continental como parte del margen continental Iberico occidental, que se centren en la evolución tectónica “reciente”, en especial aquellos que se centran en la evaluación del peligro sísmico regional
It is after the early 1980s that the research team from Lisbon University performed studies directed at the neotectonics in mainland Portugal, intended as the study of tectonic deformations occurring since the initiation of the current tectonic regime, characterized by a NW-SE trending SHmax that results from the IberiaNubia convergence along the same azimuth (Ribeiro et al, 1996, Borges et al, 2001)
The considered neotectonic activity spans a large time interval, based on the current tectonic regime, requiring the use of relatively old stratigraphic and geomorphic references to recognize and characterize the deformations accumulated since the onset of the neotectonic period – typically fluvial sediments that predate the Quaternary entrenchment of the regional drainage network and correlative raised marine sediments and abrasion platforms, of Piazencian age, along the littoral
Summary
Portugal mainland is located on the Eurasian Plate, close to the West-Iberian continental margin and the Eurasia-Nubia plate boundary (eastern sector of the Azores – Gibraltar fracture zone). Coeval ~E-W extension in the Alboran Basin at a rate of ~2mm/yr (Serpelloni et al, 2007), and left-lateral shear along the NNE trending Trans-Alboran shear zone, are not straightforward in the context of regional shortening, indicating complexity of deformation at the plate borders In this context, and based upon a number of independent observations such as detailed seafloor morphology, earthquake distribution and seismic profiles (multi-channel reflection, as well as wide angle refraction), Gutscher and others Pedrera et al (2011) question this model, defending that the eastward Gibraltar Arc oceanic subduction system is inactive probably since the Late Miocene According to these authors, the current tectonic framework in the Gibraltar Arc domain is of continental collision, with the regional intermediate seismicity being associated to part of the old, N30oE to N40oE oriented subducted slab, orthogonal to the regional convergence. As a result of the regional geodynamic setting, mainland Portugal and the nearby Atlantic area experiences moderate levels of seismicity, characterized by relatively frequent M
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