Characteristics of a new regional seismic-intensity prediction equation for Spain

An updated compilation of intensity files was performed based mainly on the most recent studies of earthquake intensity distribution in Spain [above all, the revision by Martínez Solares and Mezcua (Catálogo Sísmico de la Península Ibérica (800 a.C.-1900). Monografía No. 18, Instituto Geográfico Nacional, 2002)] and an intensity dataset generated by the Instituto Geográfico Nacional in 2008 using the Did you feel it Internet-based program. The large amount of data (more than 37,000 intensity data points) enabled us to calculate an intensity prediction equation for the whole of the Spanish mainland, as well as regional equations corresponding to three Spanish seismotectonic zones. The intensity prediction equations for the three different seismotectonic regions in the Iberian Peninsula (Betic, Stable Continental Region—SCR and Pyrenees) reflect their differences. The Pyrenees zone provides the highest maxima intensities for magnitudes M 5 and 6 in the 20–100 km range of hypocentral distance, but for that distance interval, the intensities for magnitude M = 4 shown by the SCR region is higher. Finally, when comparing the theoretical intensity values obtained using the average intensity prediction equation for the Spanish mainland with the values in the dataset, anomalous behaviour occurs in the 60–120 km range, which can be explained by the Moho bounce of the energy that increases the corresponding intensity values in this distance range. This effect is suggested also by studying the PGV amplitude decay with distance using a set of 11 shallow events in the 4.5–5.1 moment magnitude interval.