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

• A seismic swarm provides significant tectonic information for a low seismicity area.
• Relocation and field data relate the swarm source with orocline bending.
• We do not find evidence for the previously proposed triggering of the sequence.

From October 2012 to October 2013, a seismic swarm released more than 7000 microearthquakes beneath the eastern Guadalquivir foreland basin. From double-difference relocations of 501 events (md > 1.5), we can image the active structures associated with this swarm. Most of the events occurred along two ~ N–S trending lineaments separated ~ 1 km. Relocation places most events at 4–6.5 km depth in the Iberian-massif basement below the basin. Moment tensor inversion yields strike-slip mechanisms consistent with the hypocenter alignments, attributing left-lateral motion to the N–S structures and right-lateral motion to the ESE–WNW ones, in compliance with the ~ NNW direction of the main compressive stress field in the central Betics. These structures respond to a vertical-axis bend in the mountain front associated with the protrusion of Sierra Cazorla east of the epicentral area. This bend is mimicked by concordant, gentle bends in the foreland units, which are evident from the surface geology as well as through structural elements like strike-slip faults, crisscrossing joints. In this context, the right-lateral shear zone responsible for the Torreperogil sequence is taking up deformation in the western limb of the foreland bend.

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