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, Mw 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