Paleoseismic results from multiple trenching analysis along a silent fault: The El Camp fault (Tarragona, northeastern Iberian Peninsula) Resultados paleosísmicos obtenidos del análisis de trincheras en una falla silenciosa: la falla de El Camp (Tarragona, nordeste de la Península Ibérica)

We present the paleoseismological analysis of the El Camp fault scarp. Pa l e o s e i s m o l ogy constitutes the key methodology for any real estimate of seismic hazard in low-slip-rate areas with no reported historical eart h q u a kes. The recent tectonic activity of this fault is evidenced by a young mountain front and a fault scarp which cuts Quatern a ry alluvial fans. A regional geological analysis indicates that three generations of alluvial fans are cut by the fault. Absolute (TL and U/Th) and relative datings show that the oldest fan is 300 ka old and the intermediate one is 125 ka old. The study of 7 trenches and the absolute datings performed (TL, U/Th, radiocarbon as well as pollen analysis) revealed the following: 1) the El Camp fault consists of two segments (the nort h e rn end of the southern segment is located close to Po rquerola creek); 2) only the southern segment has been active since 125 ka; 3) the fault is seismogenic because it is associated with liquefaction features and colluvial wedges; 4) the El Camp fault has produced at least three well constrained surfa c e rupturing eart h q u a kes since 125 ka (events Z, Y, and X). Based on the different tectonic features observed in the trenches, the recurr e n c e period of large eart h q u a kes during this period was estimated to be around 30 ka and the elapsed time to be around 3000 yr. Using the fault length and the ve rtical displacement per event, the largest estimated eart h q u a ke had a magnitude of M W 6 . 7 .