GNGTS 2022 - Atti del 40° Convegno Nazionale

66 GNGTS 2022 Sessione 1.1 SPATIAL AND TEMPORAL EVALUATION OF THE PARAMETERS OF THE GUTENBERG-RICHTER LAW, CASE OF STUDY: ITALY A. Figlioli 1 , A. D’Alessandro 2 , R. Martorana 1 , A. Sulli 1 , G. Vitale 2 1 Università degli studi di Palermo, Dipartimento di Scienze della Terra e del Mare, Palermo, Italia 2 Istituto nazionale di Geofisica e Vulcanologia, Osservatorio Nazionale dei terremoti, Roma, Italia Introduction. In this work, calculation techniques are used to estimate the variation of the b value and the completeness magnitude both spatially and temporally. The computation of the completeness magnitude is closely related to the b value. If we underestimate the Mc, we could underestimate the b value. The parameters Mc, a value and b value are related through the Gutenberg-Richter law (Gutenberg and Richter, 1944). The completeness magnitude, known as the limiting magnitude threshold, is theoretically defined as the lowest magnitude at which 100% of earthquakes occur in a space-time volumes are detected (Mignan et al., 2012). The estimating of b value is important for the scientific community (Gulia et al., 2018; Gulia and Wiemer, 2019; Su and Han, 2021; Taroni, 2021). Studies of the b value increased in the recent years. It is thought that the b value has many significant interpretative ways out, among these there is the opportunity of using it as a precursor of possible seismic sequences (Lombardi, 2021). Other application of b value is to research the place of magma storage (Murru et al., 2007) or the association of focal mechanism. Finally, the a value, is the parameter that indicates the number of events in the catalogue, thus describing the overall seismicity of the region. In this scenario, we decided to use the earthquake catalogue, downloaded from the official earthquake website of Istituto Nazionale di Geofisica e Vulcanologia (http://terremoti.ingv.it/ ). In particular, we selected the period from 1 est January 1985 to 28 February 2022. This choice was prompted by the need to have a very large catalogue available, to be able to analyse as many periods as possible and areas of seismotectonic interest. Thanks to the use of the ZMAP software (Wiemer, 2001) that runs in a Matlab environment, we were able to extract the first maps relating to the Mc, b value and a value parameters. Especially, our goal is to test as many calculation techniques as possible in order to make reasonable comparisons and define which technique best describes the catalogue. There are many calculation techniques for the completeness magnitude, the most used are the following: MAXC (Maximum Curvature), MBS (Mc by B-value Stability), GFT(Goodness of Fit Test), EMR(Entire Magnitude Range). These techniques are based on calculation differently. In recent years, further techniques have developed that could make computing evolve in a much more sophisticated way (Taroni, 2021). Data Analysis. In the first approach, we select theMAXC, themaximum curvature technique (Wiemer and Wyss, 2000). This technique consists of evaluate the maximum curvature by computing the maximum value of first derivative of the frequency-magnitude curve. This method is fast and uncomplicated, it is very performing to a small catalogue and give a stable completeness magnitude. When using this technique in the MATLAB environment, it is possible to change the input parameters to obtain as much as possible a good estimate of the completeness magnitude. To estimate the cumulative curve the input parameters are: • Mc correction: it is a parameter that is taken into consideration to improve the estimate of the completeness magnitude. Using this MAXC technique, we tend to correct the value by bringing the estimate from the right side of the curve so that all values are representative of after this curve. • Magnitude bin width: this parameter normally is never changed, by default it is 0.1 • Min of event: it allows to select the minimum number of earthquakes that we want to represent in the curve.