Evidencias de paleo-rupturas superficiales a ambos flancos de un lomo de presión en la Falla de Alhama de Murcia (SE España)

Resum

In this study we present the first paleoseismic results along a complete transect of the frontal pressure ridge of Alhama de Murcia Fault (AMF). AMF is one of the most active faults in the Iberian Peninsula, with many evidence of historical and instrumental seismicity, and inferred slip rates between 1.0-1.7 mm/yr. It is an oblique left-lateral strike slip fault that, in some segments, ramifies into several branches. In the central segment (Lorca-Totana), the fault divides into at least 5 bran- ches, being the two frontal ones the limits of a pressure ridge. The NW branch has been previously studied in several works, while the SE branch has never been characterized; our study is the first one to provide evidence of its Holocene activity. We show the results of a 7 m deep trench in the NW branch and 5 regular trenches in the SE branch that allowed to; a) enlarge the paleoearthquake catalogue in the NW branch by interpreting a total of 13 paleoearthquakes and b) unveil the existence and Quaternary activity of the fault limiting the pressure ridge to the SE. 5 paleoevents have been identified in this branch showing cumulative vertical offsets of 4-5m. The last identified event is younger than 8-9 kyr BP based on new radiocarbon dates. The results obtained in these two sites allow identifying a partition of the deformation; the NW branch accommodates most of the lateral component and the SE branch the dip-slip component. The study also enables refining the seismic parame- ters of AMF. A more complete paleoearthquake catalogue allows reassessing the recurrence intervals assigned to this fault and the mean slip per event estimations.