 Gravimetric data highlight the geometry of the sedimentary infill of the Granada Basin, which constitutes a half-graben tilted to the N-NE. Granada Basin´s high-angle normal faults might be linked at depth to an active low-angle extensional deformation zone. The active Granada Fault zone shows low magnitude seismicity and current average vertical rate that varies from 0.4 to 1.1 mm/yr.

The tectonic structure of the Guadalquivir foreland basin becomes complex eastward evolving from a single depocenter to a compartmented basin. The deformation pattern within the eastern Guadalquivir foreland basin has been characterized by combining seismic reflection profiles, boreholes, and structural field data to output a 3‐D model. High‐dipping NNE‐SSW to NE‐SW trending normal and reverse fault arrays deform the Variscan basement of the basin. These faults generally affect Tortonian sediments, which show syntectonic features sealed by the latest Miocene units. Curved and S‐shaped fault traces are abundant and caused by the linkage of nearby fault segments during lateral fault propagation. Preexisting faults were reactivated either as normal or reverse faults depending on their position within the foreland. At Tortonian time, reverse faults deformed the basin forebulge, while normal faults predominated within the backbulge. Along‐strike variation of the Betic foreland basin geometry is supported by an increasing mechanical coupling of the two plates (Alborán Domain and Variscan basement) toward the eastern part of the cordillera. Thus, subduction would have progressed in the western Betics, while it would have failed in the eastern one. There, the initially subducted Iberian paleomargin (Nevado‐Filábride Complex) was incorporated into the upper plate promoting the transmission of collision‐related compressional stresses into the foreland since the middle Miocene. Nowadays, compression is still active and produces low‐magnitude earthquakes likely linked to NNE‐SSW to NE‐SW preexiting faults reactivated with reverse oblique‐slip kinematics. Seismicity is mostly concentrated around fault tips that are frequently curved in overstepping zones.

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We present the results of the seismic deaggregation in 15 of the most important cities with the greatest seismic hazard in the south and west of the Iberian Peninsula (Spain and Portugal). The deaggregation was carried out based on the calculation of the seismic hazard in the zone, taking into account the peak horizontal acceleration with 10% probability of exceedance in 50 years (return period of 475 years). We first performed a deaggregation study in terms of magnitude and distance in order to subsequently carry it out in azimuth. The aim of both studies is to determine the relative contribution of the different seismic foci and sources to the seismic hazard in a given location. Due to the lack of enough seismotectonic data in the study region, we could not obtain information about the contribution of specific active faults and we have not been able to include a characteristic earthquake model. However, by starting from a calculated hazard using smoothed background seismicity, it is possible to determine the contribution of the different seismic foci of the region to the seismic hazard at each location. The results reveal that there are cities where the hazard is entirely, or almost entirely, due to the local seismicity (e.g., in Portugal: Lisbon, 87%; Coimbra, 82%; in Spain: Almería, 99%; Córdoba, 99%; Granada, 99%). We have also determined that there are cities where seismic foci at 200 km away or more can be the most important or at least contribute significantly to the hazard (e.g., Beja and Faro in Portugal and Cádiz and Huelva in Spain).

Fault barriers are key structures for studying seismic hazard in regions of intense brittle deformation. The interaction between fault sets affects their seismogenic behavior, if some of them act as barriers. The Granada Basin, in the Betic Cordillera, is a region affected by shallow brittle deformation, as it was the scenario for the recent Granada 2021 seismic sequence. This seismicity presented a swarm behavior at the beginning of the sequence, followed by mainshock‐aftershock features. Geological and gravity data presented here reveal that the basement is affected by two sets of NW‐SE and NE‐SW normal faults and intensely deformed by vertical NW‐SE joints. Improved relocation of the Granada 2021 seismicity reveals a confined chimney‐shape seismicity caused by the activity of a 2 km long NW‐SE normal fault segment. The confinement of the sequence is associated with the NE‐SW fault set acting as a barrier that restricts the rupture area, limiting the maximum magnitude, and favoring the recurrence of events with smaller magnitude. The chimney‐shape of the seismic sequence suggests that the deformation is propagated vertically to the surface, facilitated by preexisting fractures. The shallow extensional deformation during the uplift of the central Betic Cordillera drove the activity of the local structures obliquely to the regional extensional trends, as evidenced by the seismic sequence. This multidisciplinary study improves the knowledge on the origin of the Granada Basin and underlies the important role of preexisting fractures on fault segmentation and seismic propagation, decreasing the seismic potential of this area.

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