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 are 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.

Physics‐Based Earthquake Simulations in Slow‐Moving Faults: A Case Study From the Eastern Betic Shear Zone (SE Iberian Peninsula)

“…A neotectonic shortening phase started at the end of the Neogene as a result of Eurasia and Africa convergence (Sanz de Galdeano, 1990; Herrero‐Barbero et al., 2020, and references therein). Present‐day convergence rate is about 4–6 mm/yr in a NW‐SE direction based on geodetic and seismological data (see e.g., Koulali et al., 2011; Nocquet, 2012; Serpelloni et al., 2007) and the EBSZ seems to be accommodating up to 31% of the total shortening (Masana et al., 2004).…”

Improved Geological Slip Rate Estimations in the Complex Alhama de Murcia Fault Zone (SE Iberia) and Its Implications for Fault Behavior

“…For instance, Herrero‐Barbero et al. (2020) have interpreted refraction as the cause of dip decrease at the surface in the NE tip of the AMF. The latter model could also be the explanation for a frontal thrust in the transect (F‐AMF) (Figure 2b).…”

“…Previous studies have suggested a structural control of preexisting Miocene extensional faults in the development of the active transpressive structure of the AMF, for instance at the NE end of the fault (e.g., Herrero-Barbero et al, 2020). Up until the Late Miocene, these faults bounded major sedimentary basins located NW of the modern AMF trace (i.e., Lorca and Fortuna basins; Figure 1c), which then inverted into oblique-reverse faults forming the related thrust-fold ranges of the Las Estancias, La Tercia and Espuña (Martínez-Díaz, 1998;Meijninger & Vissers, 2006;Montenat et al, 1987).…”

Analysis of a travertine system controlled by the transpressional activity of the Alhama de Murcia fault: The Carraclaca site, eastern Betic Cordillera, Spain

“…The AMF here has a diffuse geomorphic expression, which can be ascribed to the transfer of the deformation to the nearby Carrascoy fault. Herrero- Barbero et al (2020) estimate a net-slip rate of about 0.32 mm/year in this section for the last 4.8-7.6 Ma, based on GPS convergence vectors and cross-section restorations.…”