Anisotropic attenuation of the macroseismic intensity

Macroseismic intensity is a measure of the size of an earthquake in terms of the damages caused to the anthropic and natural environment; it is an ordinal quantity expressed through the twelve degrees of the macroseismic scale. The set of intensity values recorded in the sites around the epicenter constitutes the macroseismic field of the event, that is, the damage scenario produced by the earthquake. Knowing the expected spatial distribution of the effects of a future quake would allow to carry out prevention actions and to intervene more promptly in the case of disastrous event. At first we studied a probabilistic model for the intensity at site under the assumption that the attenuation trend was circular; actually, drawing the isoseismal lines (lines of equal felt seismic intensity) of many earthquakes we noted that the trend is quite complex and it is influenced by the ground conditions and the orographic configuration. Therefore, to generalize the shape of the isoseismal lines, we considered an elliptical trend where the major axis of the first isoseismal line corresponds to the fault. In this work we extend the previous results by proposing a method to determine location and extremes of the fault when they are unknown. Examples of the damage scenario estimated for some volcanic and recent tectonic earthquakes are given.