Seismic transpressive basement faults and monocline development in a foreland basin (Eastern Guadalquivir, SE Spain)

Abstract

We examine the late Tortonian to present‐day deformation of an active seismic sector of the eastern Iberian foreland basement of the Betic Cordillera, in southern Spain. Transpressive faults affecting Paleozoic basement offset up to Triassic rocks. Late Triassic clays and evaporites constitute a décollement level decoupling the basement rocks and a ~100 m thick cover of Jurassic carbonates. Monoclines trending NE‐SW to ENE‐WSW deform the Jurassic cover driven by the propagation of high‐angle transpressive right‐lateral basement faults. They favor the migration of clays and evaporites toward the propagated fault tip, i.e., the core of the anticline, resulting in fluid overpressure, fluid flow, and precipitation of fibrous gypsum parallel to a vertical σ3. The overall geometry of the studied monoclines, as well as the intense deformation within the clays and evaporites, reproduces three‐layer discrete element models entailing a weak middle unit sandwiched between strong layers. Late Tortonian syn‐folding sediments recorded the initial stages of the fault‐propagation folding. Equivalent unexposed transpressive structures and associated monoclines reactivated under the present‐day NW‐SE convergence are recognized and analyzed in the Sabiote‐Torreperogil region, using seismic reflection, gravity, and borehole data. A seismic series of more than 2100 low‐magnitude earthquakes was recorded within a very limited area of the basement of this sector from October 2012 to May 2013. Seismic activity within a major NE‐SW trending transpressive basement fault plane stimulated rupture along a subsidiary E‐W (~N95°E) strike‐slip relay fault. The biggest event (mbLg 3.9, MW 3.7) occurred at the junction between them in a transpressive relay sector.

The 2012–2013 earthquake swarm in the eastern Guadalquivir basin (South Spain): A case of heterogeneous faulting due to oroclinal bending

“…Stich et al, 2003;Ocaña et al, 2008). For the Torreperogil swarm, a previous tectonic interpretation (Pedrera et al, 2013) was based on an apparent E-W and NE-SW epicenter alignments, an impression that is contradicted by our locations. For earthquake swarms, relative location techniques become the method of choice, capable of resolving the seismotectonics fine structure of the source volume.…”

“…Recent contributions point out to an upper Miocene deformation associated with the progressive indentation of the western termination of the Cazorla Arc. In this western termination, and near the Torreperogil swarm, Late Tortonian strata are openly folded (Pedrera et al, 2013).…”

“…The marls thicken basinwards and alternate with bioclastic sandstone levels towards the top of the sequence. of the E-W monocline folding (Pedrera et al, 2013) related to the present-day NW-SE Iberia and Nubia convergence (Stich et al, 2006;Palano et al, 2013).…”

Changes in dip and frictional properties of the basal detachment controlling orogenic wedge propagation and frontal collapse: The external central Betics case

“…Therefore, shortening deformation lasted until at least the Messinian as the orogenic front and its foreland basin propagated farther toward NW. In addition, the positive inversion of preexisting basement normal faults in the GB (Figure b) could be associated with seismically active faults reported in this area (magnitudes 1–6 [e.g., Sánchez‐Gómez and Torcal‐Medina , ; Pedrera et al ., ; Sánchez‐Gómez et al ., ]). It is noteworthy that the earthquakes distributed along the FFTB‐GB boundary show focal mechanisms congruent with the ENE‐WSW reverse faults and NNW‐SSE normal faults [ Sánchez‐Gómez and Torcal‐Medina , ].…”

Statistical analysis of the 2012–2013 Torreperogil–Sabiote seismic series, Spain

“…According to the seismic record, this area was considered as a zone of low seismic activity (Cantavella et al 2013). Some authors (e.g., Pedrera et al 2013) indicate the presence of basement faults and suggest their activation during the TS-1213 series. The epicentral area was located within the eastern Guadalquivir basin, beneath an elongated ridge known as Loma de Ubeda, between the towns of Torreperogil and Sabiote.…”