Search

Palaeoseismological studies play a crucial role in the seismic characterization of regions with slow-moving faults. This is the case in the central Betic Cordillera, a highly populated area for which the record of prehistoric earthquakes is very limited, despite being one of the regions with the greatest seismic hazard in Spain. We present here a palaeoseismological characterization of the Galera Fault, one of the active faults accommodating deformation in the central Betic Cordillera. We excavated and analysed several trenches along the fault trace. We quantitatively correlate the results from these trenches, resulting in a surface rupture history involving seven or eight events (accounting for the epistemic uncertainties) during the last ca. 24 000 years, with recurrence intervals ranging from 1520 to 1720 years. Further analysis of this surface rupture history seems to indicate that the Galera Fault is prone to producing earthquake clusters as we recorded five events in ∼400 years (ca. 1536–1126 BCE) and only two events in the ∼3200 years that followed. Using the fault geometry and palaeoseismological data, we also carried out a seismogenic characterization of the fault. This analysis yielded a maximum expected magnitude of 6.7 ± 0.3 and a recurrence interval of 1857 years. Furthermore, we also present a geodetic rupture scenario for the maximum expected event, involving displacements of up to 0.5 m. Finally, we discuss the possible impact of the deduced palaeoearthquakes on the development of Bronze Age human settlements located in the vicinity of the fault. In addition to their intrinsic value, our results will provide the basis for future seismic-hazard assessments carried out in the central Betic Cordillera.

The geometry and kinematics of active faults have a significant impact on their seismic potential. In this work, a structural characterization of the active Baza Fault (central Betic Cordillera, southern Spain) combining surface and subsurface data is presented. Two sectors are defined based on their surface geometry: a northern sector striking N–S to NNW–SSE with a narrow damage zone and a southern sector striking NW–SE with a wide damage zone. A kinematic analysis shows pure normal fault kinematics along most of the fault. Geometric differences between the northern and southern sectors are caused by i) a heterogeneous basement controlling the fault geometry at depth and in the cover; ii) different orientations of the Baza Fault in the basement with respect to the regional extension direction and iii) interaction with other active faults. We use this structural characterization to analyse the segmentation of the Baza Fault. According to segmentation criteria, the entire Baza Fault should be considered a single fault seismogenic segment. Consequently, the seismic potential of the fault is defined for a complete rupture. Magnitude for the Mmax event is calculated using several scale relationships, obtaining values ranging between Mw 6.6 and Mw 7.1. Recurrence times range between approximately 2,000 and 2,200 years for Mmax events and between 5,300 and 5,400 years for palaeo-events. A geodetic scenario modelled for an Mmax event of Mw 6.7 shows permanent vertical displacements of more than 0.40m and an overall WSW–ENE extension during entire ruptures of the Baza Fault.