Avalanchas de rocas inducidas por tectónica activa Cuaternaria en la Sierra de la Sobia (Cordillera Cantábrica, NO Iberia)

Resum

Sierra de la Sobia is a structural relief of carboniferous limestone and ca. 20 km length, developed in the León Thrust footwall by the N-S Alpine tightening of the late-Variscan orocline known as Cantabrian Arc (CA). The study of 9 rock avalanches, triggered along the south-western and southern hillslope, revels the current active tectonic of the strike-slip minor (metric displacement) faults. These faults are trending transvers and parallel to CA and they are cutting one splay trace of the León Thrust. The avalanche deposits consist in unless three accumulation bodies superpose. U-Th dating carbonate of the coated limestone blocks yield interglaciers Marine Isotopic Stages (MIS) from MIS 9a to MIS 1. The not cemented blocks deposits overlaying the cemented deposits suggests the Holocene recurrence of such faults. The strike-slip fault traces have maxima lengths < 3 km and < 70 m of maxima strike separation. The fault slip inversion engenders a compressive regime, charac- terised by the N-S trending of the maximum horizontal stress (SHmax), which is consistent with the current fault kinematics. The recent deformation of Sierra de la Sobia is restored, assuming longitudinal tangential strain with the neutral line locates along the range summits line (RLS). Current tightening of the range extends 300 m its outer arc. The whole angular extension of 3.32º of along the convex south-western hillslope of the range is in balance with the rigid throw of the transverse strike-slip faults from the restored RLS.