Archaeoseismologic Analysis of a Late Bronze Age Site on the Alhama de Murcia Fault, SE Spain

Abstract

An archaeoseismological study of Tira del Lienzo (Totana, Spain) was undertaken. The site belongs to the Argar archaeological group (2200 1550 cal. B.C.; Bronze Age). It is located on the trace of the reverse left-lateral Alhama de Murcia fault (AMF) that was responsible for the 5.1 Mw 2011 Lorca earthquake. The constructive typology of the site consists of mortar-free irregular natural boulders (dry-set masonry) and differs from earlier archaeoseismological sites built on regular masonry constructions in the Betic Cordillera. Four Earthquake Archaeological Effects (EAEs) were identified as follows: (1) an apparent surface rupture (c. 18 cm left-lateral offset), (2) the differential coseismic uplift of several centimeters affecting the main building of the settlement, (3) the widespread development of fractures on the ground surface (ground cracks) in a NE-SW direction consistent with the kinematics of the AMF, and (4) fractures in boulders that constitute the remains of the dry stone walls at the site. Structural analysis of the two fracture types reveals two nearly orthogonal sets (NE-SW and NW-SE), matching the strike-slip kinematics of the AMF in the zone. Archaeoseismic evidence and related radiocarbon dates of the different building phases of the Bronze Age site indicate the probable occurrence of at least one strong seismic event (6.3 6.5 Mw; IX ESI-07) around 1550 cal. B.C., or soon after, triggering the destruction and probably the eventual abandonment of the site. We have identified an ancient lost earthquake from the Bronze Age and report the first archaeoseismological evidence of surface rupture in the Iberian Peninsula. This study also provides the first numerical data in the Totana-Alhama segment of the AMF based on the recorded archaeoseismic displacements. These data allowed us to characterize the related slip rates (0.05 mm/yr) to define the seismic potential of the analyzed fault segment of the AMF, which was poorly defined by previous seismic and geological data.