Quaternary earthquake evidence into an hypogenic cave: The benís cave (murcia, se of spain)

Abstract

The interaction between karst hypogenic processes and Late Pleistocene active faulting determines the present topography and shape of the Benís Cave within the Cieza Ranges in the eastern Betic Cordillera (SE Spain). This cave represents the explored deepest cave within the Murcia region, reaching the deepest point at-320 m, and showing “in situ” fossil remains of mammal carnivores (Lynx pardinus spelaeus) as well. In addition, this cave displays evidence of paleoseismic activity from broken speleothems, but also from instrumental earthquakes collapsing the cave ceiling hall at-150 m depth (1999 Mula Event). The geometry and speleogenesis of Benís cave from the Late Pleistocene is a combination of two processes: (1) a shallow hypogenic origin related to upwards movement of confined aquifer located between 0 and 150 m depth, with lots of outlets and megascallops, and (2) a deep fault-cave related to the Benís fault developed between 150-320 m depth. This fault is N-S trending with normal kinematics and evidence of Late Pleistocene paleoseismic activity. Related to this, different fossil bones of Lynx pardinus spelaeus, was found in situ, which were dated by amino acid racemization in 65 ± 17.6 ka (OIS 4). The estimated size of the last paleoearthquake was around 6 Mw according to the measured coseismic displacement at depth and the length of the Benís fault trace at surface. The combination of the two processes (hypogenic confined aquifer and a seismogenic faulting), controlled the development, geometry and speleogenesis of the Benís Cave during at least the last 250 ka.