Caracterización geológica de la falla del Llano del Águila en Campo Dalías (Almería)Posible fuente sismogénica del terremoto de 1804

Abstract

On August 25, 1804, an earthquake with a Mw ~6.4 and a maximum intensity of IX, caused serious damage in several locations of Campo de Dalías region (Almeria) This study provides new evidence of the relationship between this episode and the Llano del Águila fault. A NW-SE subvertical fault, with a normal-dextral slip, that runs parallel to the Loma del Viento fault, located at about 3 km to the south. For the characterization of the Llano del Águila fault, a new geomorphologic interpretation of the Quaternary alluvial deposits and their relationship with the trace of the structure has been carried out. Four generations of alluvial fans draining the Sierra de Gádor and two fault sections have been identified at a cartographic scale (Cantera Est and Rambla de la Maleza). All the geomorphologic interpretation is made by the analysis of historical aerial photos. Due the high anthropization of the area, modern elevation models are not sufficiently useful. To overcome this limitation, a digital elevation model was obtained through photogrammetry with the aerial photos of the interministerial flight (1977). Fault scarp analysis from topographic profiles measured on the new elevation model provides a 6.3 ± 1.9 m vertical slip for the Cantera East section and a 12.1 ± 1.9 m vertical slip for the Rambla de la Maleza section. All these interpretations have been verified in the field and new data on the kinematics have been acquired to estimate the net slip rate of each section. A 0.016 ± 0.002 – 0.10 ± 0.02 mm/yr slip rate has been estimated for the Cantera Est section and a 0.031 ± 0.002 – 0.19 ± 0.02 mm/yr for the Rambla de la Maleza one, for the last 126 – 781 ky (middle Pleistocene). A maximum magnitude of 6.59 ± 0.19 is estimated through empirical relationships from the total length of the fault trace.