We critically analyzed the results of previous studies on seismic intensity attenuation in Italy performed by some of us. Although no mistakes were made in such works, we demonstrate here that they do not reproduce the real behavior of seismic intensity with distance from the source due to the inadequacy of some of the assumption made. We also propose some recipes that can be useful to obtain unbiased estimates of the attenuation properties and also significantly improve the goodness of fit with data: 1) Intensity data located at distances from the source for which an intensity value below the limit of diffuse perceptibility (about IV) is expected makes the resulting attenuation function to overestimate intensity at large distances. Thus, for an unbiased estimate, such data have to be excluded from computations. 2) Epicentral intensities Io reported by the Italian catalog (computed as the maximum observed one or little less when site amplification was supposed to occur) overestimates the intensity predicted by attenuation laws at the epicenter of about one intensity degree on average and then need to be recomputed consistently. 3) A possible way to make epicentral intensity consistent with the intensity expected at the epicenter is to define it as Io=Iav-g(h)+g(Dav) where g(x) is the functional representing the distance dependence of seismic intensity, h the source depth, Iav and Dav respectively the averages of the observed intensities and the epicentral distances, computed over all intensity data of each earthquake. The application of these recipes to the same dataset used in previous studies decreases the model residual mean square of more than 30%.
Pasolini C., Gasperini P., Albarello D., Lolli B., D’Amico V. (2006). The attenuation of seismic intensity in Italy: theoretical and empirical backgrounds. ZURICH : ETH.
The attenuation of seismic intensity in Italy: theoretical and empirical backgrounds
PASOLINI, CHIARA;GASPERINI, PAOLO;LOLLI, BARBARA;
2006
Abstract
We critically analyzed the results of previous studies on seismic intensity attenuation in Italy performed by some of us. Although no mistakes were made in such works, we demonstrate here that they do not reproduce the real behavior of seismic intensity with distance from the source due to the inadequacy of some of the assumption made. We also propose some recipes that can be useful to obtain unbiased estimates of the attenuation properties and also significantly improve the goodness of fit with data: 1) Intensity data located at distances from the source for which an intensity value below the limit of diffuse perceptibility (about IV) is expected makes the resulting attenuation function to overestimate intensity at large distances. Thus, for an unbiased estimate, such data have to be excluded from computations. 2) Epicentral intensities Io reported by the Italian catalog (computed as the maximum observed one or little less when site amplification was supposed to occur) overestimates the intensity predicted by attenuation laws at the epicenter of about one intensity degree on average and then need to be recomputed consistently. 3) A possible way to make epicentral intensity consistent with the intensity expected at the epicenter is to define it as Io=Iav-g(h)+g(Dav) where g(x) is the functional representing the distance dependence of seismic intensity, h the source depth, Iav and Dav respectively the averages of the observed intensities and the epicentral distances, computed over all intensity data of each earthquake. The application of these recipes to the same dataset used in previous studies decreases the model residual mean square of more than 30%.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
