GNGTS 2021 - Atti del 39° Convegno Nazionale

39 GNGTS 2021 S essione 1.1 INSIGHT ON SEISMIC HAZARD: A CUTTING-EDGE FRAMEWORK FOR SEISMIC COUPLING COEFFICIENT COMPUTATION B.G. Galuzzi 1 , F. Sparacino 2,3 , M. Palano 2 1 Dipartimento di Bioscienze e Biotecnologie, Università degli Studi Milano-Bicocca, Milano, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo - Sezione di Catania, Catania, Italy 3 Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università degli Studi di Catania, Catania, Italy Introduction. In the last two decades, the continuous worldwide growth of GNSS and seismic networks allowed the acquisition of extensive seismological and geodetic datasets. This amount of data permitted several studies, which have highlighted the usefulness of scalar geodetic and seismic moment-rates estimations and comparisons over different tectonic settings (e.g., Maz- zotti et al ., 2005, D’Agostino 2014, Sparacino et al ., 2020 and references therein). The basic idea is that, for a given region, the moment released by earthquakes mirrors the rate of tectonic deformation (Kostrov, 1974). Achieved results have allowed to identify regions where the crustal deformation budget is entirely released by seismicity (e.g. Mazzotti et al ., 2011; Pancha et al ., 2006; D’Agostino, 2014; Sparacino et al ., 2020), as well as regions where the excess deformation can be released either as aseismic slip across faults or through large future earthquakes (Masson et al ., 2005; Palano et al ., 2018, 2020, Déprez, et al ., 2013). The seismic and geodetic moment-rates ratio is usually expressed in percentage and termed as seismic coupling coefficient (SCC): a low value of SCC implies that the geodetic moment-rates are larger than the seismic ones, while a high value of SCC means that the seismic moment-rates are larger than the geodetic ones. The estimation of SCC relies on the computation of intermedi- ary parameters (e.g. seismogenic thickness, max strain-rates, maximum magnitude, and a and b parameters of the Gutenberg-Richter law) which can require a huge amount of time and effort, especially if large areas are considered. To the best of our knowledge, there is no specific tool, which integrates all these elements in an efficient and effective way for the computation of SCCs. Here, we have developed a Matlab- based framework, which allows us to estimate the SCC values over large regions fastly. However, such a framework is general and could be applied to any possible area of interest. The framework. The framework takes as input available (historical and instrumental) seismic catalogs and geodetic velocity data. A generic grid is used to divide the area to analyze. Such a grid is formed by uniform rectangular cells. After setting few computational parameters (e.g., grid size, earthquake magnitudes and depth cut-off), we are able to obtain as outputs for each grid cell: - the SCC values, i.e. the simple seismic/geodetic moment-rates ratios; - the geodetic strain and moment-rates, estimated by using the Savage and Simpson (1997) for- mulation; - the seismic moments-rates, estimated by using i) the moment summation approach of Kostrov (1974) and ii) the cumulative truncated Gutenberg-Richter distribution described in (Hyndman and Weichert, 1983); - the parameters a and b of the Gutenberg-Richter law, estimated by using several fitting meth- ods (e.g. the maximum likelihood method and a robust linear fitting method); - the magnitude of completeness, i.e. the value where the earthquake frequency-magnitude distribution breaks down and below which the number of detected earthquakes is usually con- sidered incomplete; - the seismogenic thickness, i.e. the depth above which a given percentage (e.g. 90%, Miller and Furlong, 1988; 95%, Williams, 1996) of the hypocenters or the moment release within a depth column occurs.