New insights on the seismogenic potential of the Eastern Betic Shear Zone (SE Iberia): Quaternary activity and paleoseismicity of the SW segment of the Carrascoy Fault Zone

Abstract

The Carrascoy Fault (CAF) is one of the main active faults that form part of the Eastern Betic Shear Zone, a 450 km fault system that accommodates most of the convergence between the Eurasian (Iberia) and Nubian plates in the Betic Cordillera, south Spain. Although the CAF represents a major earthquake threat to the nearby City of Murcia, studies on its Quaternary tectonics and seismogenic potential are scarce to date. We present evidence that supports the division of the CAF into two overlapping segments with contrasting tectonic structure, Quaternary activity, and landform control: a SW segment, characterized by a broad fold-and-thrust zone similar to the forebergs defined in the Gobi-Altai region, and a NE segment, characterized by a sharp mountain front controlled by strike-slip tectonics. We attribute the differentiation into these two segments to the stresses associated with topography, which in turn is a consequence of the shortening component, at the middle Pleistocene, after circa 217.4 ka. For the SW segment we infer the occurrence of 9 to 11, M w 6.7 paleoearthquakes in the last 30.2 kyr, and a slip rate of 0.37 ± 0.08 m/kyr. We date the occurrence of the last surface rupture event after 2750 B.P., and we estimate an average recurrence period of major events of 3.3 ± 0.7 kyr.

How Much Nubia‐Eurasia Convergence Is Accommodated by the NE End of the Eastern Betic Shear Zone (SE Spain)? Constraints From GPS Velocities

“…As the fault zone strikes ENE‐WSW, the orientation and module of the velocity vectors seem to point to an oblique reverse‐sinistral kinematics of the BSFZ. This finding is in agreement with the kinematics of the Carrascoy Fault deduced based on surface geological observations (Martin‐Banda et al, ); this fault is located along the EBSZ in the western extension of the Bajo Segura Fault (Figure ).…”

“…Studies of active tectonics indicate that the EBSZ (Figures and ) is the main onshore tectonic structure accommodating the NNW–SSE plate convergence in the Eastern Betic Cordillera (Alfaro et al, ; De Larouzière et al, ; Martin‐Banda et al, ; Martínez‐Díaz et al, ; Masana et al, ; Silva et al, ). Our GPS study, which is located at the NE end of the EBSZ, shows that the mean shortening rate in the Bajo Segura Basin is 0.6 ± 0.2 mm/year.…”

Modelling earthquake rupture rates in fault systems for seismic hazard assessment: The Eastern Betics Shear Zone

“…Contrarily, the EBSZ faults show many evidences of brittle deformation that splay upwards to the free surface, indicating rapid deformation (e.g. as seen in trenches by Ferrater, 2016;Martín-Banda et al, 2015;Martínez-Díaz et al, 2018). iii) There is no evidence of historical offsets, even small, in anthropic structures (walls, roads, etc.)…”

“…Several studies at the EBSZ (e.g. Ferrater, 2016;Insua-Arévalo et al, 2015;Martín-Banda et al, 2015;Martínez-Díaz et al, 2003, 2018Masana et al, 2004Masana et al, , 2018Moreno, 2011;Ortuño et al, 2012) have evidenced the occurrence of recurrent morphogenetic earthquakes. Recent studies have also proposed considerably high slip rate values for some of these faults: 1.0 ± 0.2 mm•yr −1 (paleoseismological 3D trenching) and 1.6-1.7 mm•yr −1 (geomorphological analysis) for AMF (e.g.…”

“…More and higher precision paleoseismic parameters are available nowadays thanks to several paleoseismic studies conducted in the last decade (e.g. Ferrater, 2016;Insua-Arévalo et al, 2015;Martín-Banda et al, 2015;Martínez-Díaz et al, 2018). Recently, Rivas-Medina et al (2018) proposed a hybrid approach that avoids setting an arbitrary cut-off magnitude for distributing seismic moment between faults and zones and, at the same time, ensure that this distribution of seismic potential is not double-counted.…”