Intensity-attenuation relationships for strong Apennines earthquakes: questioning the stability of regression coefficients over time and space based on MCS and ESI scales

The reliable evaluation of historical earthquakes is pivotal for seismic hazard assessment, and macroseismic observations are the only data available for the estimation of location and magnitude of historical events . Seismic parameters for pre-instrumental earthquakes included in the Italian catalogue (CPTI15, Rovida et al., 2016) are estimated on the basis of well-constrained empirical relations between Io and Mw, and also through dedicated algorithms (i.e., Boxer code; Gasperini et al., 1999; 2010). However, the application of traditional, damage-based macroseismic scales (i.e., MCS – Mercalli Cancani Sieberg; MMI – Modified Mercalli; EMS98 – European Macroseismic Scale) to contemporary earthquakes suffer some limitations such as the saturation at higher degrees and a strong dependence on the spatial distribution of human settlements . Most pertinent for this research, these scales are significantly influenced by the large variability of building vulnerability as a function of age and local economy. In this sense, the seismic sequence occurred in Emilia Romagna region in 2012 is particularly relevant . Seismic parameters estimated from the MCS and EMS survey do not match those instrumentally recorded or expected from the application of general empirical regressions (e.g., Galli et al., 2012; Graziani et al., 2015). This has been attributed to the concomitant role exerted by the local geologic setting and the characteristics of the building stock, or to overestimated intensity of strong seismic events in the historical catalog. A complementary approach is provided by the ESI07 (Environmental Seismic Intensity) scale. This scale is based solely on Earthquake Environmental Effects (EEEs), which have the significant advantage of A) still increase in their dimensions also close to full scale and B) to respond consistently in time and space, in particular when the study area shows homogeneous structural, lithological and climatic setting (Michetti et al., 2007). The goal of this note is twofold: (i) evaluate the reliability of EEEs attenuation with distance using a preliminary dataset of Italian strong earthquakes with normal kinematics and (ii) pursue the integration of MCS and ESI scales, which results in a more comprehensive picture of the historical and modern seismic events. We focus on the MCS scale, for which a much larger database is available; arguably, the preliminary results described in the following apply also to the other major damage-based scales (Michetti et al., 2004).