Attenuation of intensity with epicentral distance in the Iberian Peninsula

We have classified the attenuation of the Medveded, Sponheuer, and Karnik (MSK) intensity into five types (each as a function of the epicentral intensity I-o) based on the mean radii of 254 isoseismal maps, mainly historical earthquakes in the Iberian Peninsula. Geographically representing each earthquake with its corresponding attenuation tendency, it can be seen that those with low attenuation lie west of the Peninsula and those with high attenuation in the south and east. This regionalization seems to be due as much to the seismotectonic characteristics (different crustal types and size of the earthquakes) as to the different construction types in each region. These attenuation values are similar to those of southern Europe, but much higher than those found in the United States. From the point of view of seismic-hazard evaluation, these laws represent an improvement with regard to those used so far. We have extended previous attenuation studies to the whole of the Iberian Peninsula, and, in some points, differences of attenuation assignment of almost two degrees of intensity have been corrected.