Active faulting and neotectonics in the Baelo Claudia area, Campo de Gibraltar (southern Spain)

The Strait of Gibraltar area is part of the western Eurasian-African convergence zone characterized by a complex pattern of deformation, including thrusting and folding and active normal faulting. Generally, the area is of low-seismicity; only some minor earthquakes have been recorded in the last hundred years. Archaeoseismological data evidences earthquake destruction occurring twice during Roman times. A better neotectonic framework and knowledge on the paleostress evolution of the Strait of Gibraltar area is necessary to find the local sources for those events and to establish an understanding of the recent deformation. Paleoseismic evidence for one moderate earthquake event around 6000-5000 BP along the normal Carrizales Fault is described in this paper. Off-shore high-resolution seismic investigations, structural and paleostress data, high-resolution GPR and geoelectrical resistivity measurements, outcrop investigations and trenching studies are discussed. The data reveal that active faulting takes place along N–S trending normal faults. Hence, N–S directed normal faults in the area are claimed as local candidates for moderate earthquake activity. Return periods of moderate earthquakes in the order of at least 2000–2500years in the study area may have to be taken into account. Structural data, such a paleostress data and joints are presented and a deformation history for the Strait of Gibraltar area in southern Spain is developed in this study. ► Off-shore and on-shore geophysical data allow determining fault geometries. ► Structural data on the changing stress field. ► N–S trending faults are the youngest tectonic elements in the area. ► Paleoseismic data yield earthquake return periods in the order of 2000–2500years.