Evidence for a 4700–2100 BC palaeoearthquake recorded in a fluvial-archaeological sequence of the Segura River, SE Spain

The archaeological excavation of a rock shelter (Abrigo del Pozo) in one of the slopes of the Segura River (SE Spain) has revealed a exceptionally preserved sedimentary record spanning from the Paleolithic to the present-day, which includes an anomalous layer of stones (RFB) fallen from the roof. The sedimentary analysis of the stratigraphic sequence exhumed by the excavation indicates that human occupation of the rock shelter was controlled by fluvial environmental evolution. However, the RFB level resulted in a disturbance of human occupation and normal fluvial sedimentation. From the sedimentary and archaeological pieces of evidence, the RFB level has been interpreted as related to a palaeoearthquake responsible for the collapse of the roof and walls of the rock shelter. The palaeoearthquake has been dated between 5820 ± 50 BP, the 14C age of the Neolithic occupation level directly below the RFB, and 3710 ± 40 BP, the 14C age of the Chalcolithic level above the RFB. A nearby earthquake of M 5.5–6.5 appears as the most plausible cause for the shelter collapse. These data suggest that the seismic activity of this sector in the eastern Betics has been continuous during the Holocene, but with larger magnitudes than the ones instrumentally recorded nowadays. More palaeoseismic data are required to determine whether or not regional faults, such as the nearby Socovos Fault, are silent faults with a discontinuous seismic behaviour that could modify the current hazard assessment.