The seismogenic zone of the continental crust in Northwest Iberia and its relation to crustal structure

Abstract

The distribution of seismicity at the western end of the Cantabrian mountain range (NW Iberia), reflecting current crustal dynamics, is investigated integrating seismically active structures, long-term structures, and the topographic features at the surface. The thickness of the seismogenic zone within the continental crust is established in 20 km. Two crustal domains can be distinguished in the study area in terms of the seismicity pattern, the style of Alpine structures and the relief. The presence of crustal fluids arises as a very likely contributing factor to the excessive thickness of the seismogenic zone in the study area. More importantly, a switch in tectonic style at the transition between crustal domains in coincidence with the lateral termination of orogenic frontal thrusts is envisaged as involving sufficient stress heterogeneity and amplification to explain the current concentration and characteristic pattern of historical seismicity in the region. Overall, the distribution of seismicity in the crust is sensitive to the type and style of crustal structures.