Neogene basin inversion and recent slip rate distribution of the northern termination of the Alhama de Murcia Fault (Eastern Betic Shear Zone, SE Spain)

Abstract

The Alhama de Murcia Fault is one of the main active structures of the Eastern Betic Shear Zone (SE Spain), characterized by the presence, along its trace, of Neogene basins developed under Early to Late Miocene extensional tectonics. A dominant NNW‐SSE shortening direction is active from Late Miocene driven by the present‐day plate convergence. We present the structural analysis of the northeastern section of this fault, where reliable estimations of slip rates were unknown due to the lack of geomorphological evidence of recent activity. The recent tectonic evolution and reactivation of the northeastern section is closely related to the Fortuna basin development and tectonic inversion. We approach the structural analysis through the interpretation of seismic reflection profiles, well data, fieldwork and 3D geological modeling. We estimated a maximum long‐term slip‐rate of (0.32 +0.18/‐0.13) mm/yr in the Librilla sector (last 4.8‐7.6 Ma), based on cross‐section restorations and assuming current motion trends from GPS data. According to the results from the cross‐sections restored along the section and a vertical displacement analysis based on a 3D model, the slip‐rate distribution shows a decrease of activity toward the northeastern tip of the studied fault section. This supports a transference of deformation between the Alhama de Murcia Fault and the Carrascoy Fault, which seems to absorb part of the shortening during the Plio‐Quaternary, explaining the lower relief created by the activity of the northeastern section. The slip rates obtained have important implications in seismic hazard assessments and in the distribution of deformation along the region.