Influence of salt-related mechanical layering on the seismic potential of active faults: Insights from the southwestern Valencia Trough (W Mediterranean)

Abstract

We present a structural and seismotectonic analysis of active faults in the southwestern Valencia Trough (western Mediterranean) on the basis of subsurface datasets. In our study, we identify and characterise three major active faults: the Cullera Fault, with long-term slip rates that vary over time between 0.15 ± 0.1 and 0.4 ± 0.1 mm yr−1; the oblique Albufera Fault, with a long-term slip rate of 0.2 ± 0.1 mm yr−1; and the normal Valencia Fault. The seismogenic character of the southwestern Valencia Trough is controlled by a mechanically weak layer consisting of Triassic evaporites. This weak layer induces partial-to-complete decoupling between the suprasalt and subsalt successions, leading to two distinct mechanisms driving fault displacement: tectonic activity and salt withdrawal. A quantitative evolutionary analysis of the Cullera Fault reveals that these two mechanisms occur alternately over time. The presence of a mechanically weak layer has implications for seismicity. Earthquakes can nucleate within both sub- and suprasalt successions, with total or partial decoupling influencing rupture propagation. We discuss how these two scenarios lead to different earthquakes and thus impact the seismic hazard of a region. Empirical source-scaling relationships, which are commonly used to estimate the seismogenic potential of active faults, generally assume a homogeneous seismogenic crust. To address this limitation, we propose a methodological approach based on the use of the aspect ratio. Using this method, the maximum magnitudes for suprasalt ruptures are 5.8–6.4, 5.4–6.2, and 5.1–5.9 for the Cullera, Valencia, and Albufera faults, respectively. These values are 11 %–25 % lower than those obtained by considering the rupture of the entire seismogenic crust. Our findings highlight the need to incorporate stratigraphic mechanical layering into seismic hazard assessments, particularly in salt-influenced tectonic settings.