The geomorphic erosive record of past earthquakes: Examples from the Palomares Fault (Almería-Murcia, SE Spain).

The Palomares fault (PLF) in SE Spain is the first tectonic structure with recognized quaternary activity within the Iberian Peninsula in the early 1970 decade. Together with the well-known Lorca-Alhama de Murcia fault (LAF) delineates the so-called Eastern Betic Shear Zone, a large (>180 km length) crustal scale left-lateral strike-slip fault zone crossing-cut across the Betic Cordillera in a SSW-NNE orientation and subject to present low strain and convergence rates (< 4 mm/yr). Whilst the LAF displays clear evidence of Holocene tectonics and historical to recent seismic activity (i.e., 5.1 Mw 2011 Lorca Earthquake), the PLF present scarce to null instrumental seismic records. However, the PLF shows relevant geomorphic and stratigraphic evidence of past Middle to Late Pleistocene seismic activity and scarce historical seismic records. Only the strong EMS X 1518 AD Vera Earthquake in Almería (6.7 Mw) can be theoretically related to this fault, but present seismic records are nearly null.

The present contribution provides support for the recurrent paleoseismic activity of the PLF during the Middle-late Pleistocene with clear morpho-stratigraphic records between the vicinity of the village of Palomares to the south (Almería) to northern localities, such Purias (Murcia). This means about 60 km of Quaternary tectonics nicely preserved in a fault segment, which has been recently considered no-faulted by theoretical approaches based on geophysical-gravity data. Whatever the case, the present contribution indicates that quaternary faulting occurs along the entire fault length, but the degree of fault activity (in timing and slip) largely decreases from south to north.  Fault kinematics also varies from nearly pure left-lateral strike-slip to a dominant reverse component south to north according to the progressive westerly bending of the PLF trace. Is in the northern segment where older deformations are present and erosional processes (i.e. gullying) nicely interplayed with fault activity generating deep furrows along the fault zone later refilled by renewed alluvial sediments and subsequently deformed by repeated paleoseismic activity. In other words, the PLF shows unique examples of the erosive record of past earthquakes, illustrating the potentially rich variety of geomorphic evidence for past seismic activity in low strain regions, even in absence of the typical tecto-sedimentary fault records, common in southern locations of this fault.

Acknowledgements: This contribution is supported by the Spanish Research Project I+D+i PID2021-123510OB-I00 (QTECIBERIA-USAL) funded by the MICIN AEI/10.13039/501100011033/.