A distribution-free analysis of magnitude-intensity relationships: an application to the Mediterranean region

A statistical analysis of the relations between macroseismic intensity and magnitude is presented. The examined data set contains earthquakes characterized by epicentral or maximum intensity greater than or equal to VI which occurred in the Mediterranean region. As a first step, an empirical magnitude-intensity relationship has been determined by using the whole data set. Then, differences between experimental magnitude values and the ones expected on the basis of the empirical relationship have been correlated with some features related both to physical and data sources characteristics. On this basis, a distribution-free statistical approach has been developed to attempt a regionalization of the examined area, able to locally optimize the performances of magnitude-intensity relations. However, the results showed that data relative to larger events (intensity greater than or equal to VII) are not sufficient to perform any reliable zonation of the area. Thus, well-constrained relationships determined for the whole Mediterranean region should be preferred to ill-defined local ones. Concerning smaller earthquakes (intensity VI), the analysis suggests that an efficient zonation could only be obtained if medium-scale variations (lower than 200 Km) are taken into account. (C) 1999 Elsevier Science Ltd. All rights reserved.