Parameters estimation of intensity decay relationships

This paper presents a methodology that analyses a set of observed intensities and estimates the parameters of an adopted attenuation law directly using the data points. A procedure was developed to define and evaluate the equivalent radii Di of the isoseismal lines. From these data it is possible to derive the parameters of the attenuation law. Moreover a validation procedure was developed to measure the capability of intensity decay relationships to reproduce the observed intensities. A case study of 55 earthquakes, divided into 9 subsets, of similar-attenuation zones, was analysed, using, as attenuation law, the one proposed by Grandori (1987, l991) to estimate either the parameters for each single earthquake or the parameters of an average intensity decay relationship for the similar-attenuation zones. The calculated intensity decay relationships result in 60- 70% of correctly reproduced points for most intensity data maps analysed. Analysing the similar-attenuation zones and different earthquakes simultaneously, the parameters of attenuation laws obtain results with a lower percentage of correctly reproduced points. The proposed methodology seems to be effective and suitable to reach practical results in parameters estimation of intensity decay relationships.