GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 corresponding to the Richter magnitude scale for the Cuban territory, was proposed by Moreno and González (2001) and was based on the analysis of earthquake records using data from the old short-term statons installed at that tme, which were quite limited in quantty and quality. Later, the seismic network was upgraded and converted to digital technology with the installaton of broadband statons, which increased the staton density in southeastern Cuba and enabled the calculaton using digital recordings. With the new database, Moreno (2002) updated the parameters of the M L considering a new data set. This equaton is currently used by the Centro Nacional de Investgaciones Sismológicas (CENAIS). However, in the last 20 years, new statons with new instruments with higher amplifcaton and wider frequency response and dynamic range have been established in the same study region (Diez Zaldívar et al., 2014 and 2022). To date, no comprehensive method has been developed in Cuba to estmate the parameters of the ML equaton using many seismic statons and many years of recorded data. For this reason, it was necessary to carry out a study to recalibrate the parameters of the M L equaton with high accuracy and with a focus on the southeastern part of Cuba. This study covered a geographical area between 19°–22° N and 73°–79° W. In this area, the predominant seismicity is characterized by an “interplate” behavior related to the Oriente fault zone, with a higher frequency of earthquakes that can reach a large magnitude (Mw > 6.0) and a depth of more than 20 km. More than 90% of the earthquakes that strike the country occur in this southeastern area of Cuba (Alvarez and Menendez, 1969; Alvarez and Bune, 1977; Moreno et al., 2002). However, moderate seismicity has also been associated with smaller faults in the interior of Cuba, which have caused some moderate earthquakes with signifcant damage (Chuy, 1999). The data comes from the general catalog of the Cuban seismological service CENAIS (2023). Between 2011 and 2021, more than 60,000 earthquakes with fairly well-defned parameters were analyzed by CENAIS seismologists and diferent signal processing methods were applied, such as fltering, deconvoluton with the instrument transfer functon and simulaton of the WA seismometer by the SEISAN sofware (Havskov and Otemoller, 2000). Our selecton (M L in a range between 2 and 5 and at least four triggering statons) includes 7750 seismic events, and the fnal input dataset contains a total of 33 916 records with: Event ID, date, depth, horizontal component amplitudes, calculated epicentral hypocentral distance, and the number of statons recorded for each seismic event. We set up the whole procedure of linear regression analysis in the Matlab environment, following Chovanová and Kristek (2018), to obtain the formula for the local order of magnitude in the IASPEI form. In a 3-step procedure, we: 1) removed the outliers; 2) searched for the parameters n, K and Si that minimize the unbiased sample standard deviaton of the residuals; c) set the anchor point for the parameter C (1/100 millimeter at 17 km). The new formula for the local parameter M_L is thus defned as follows: M L = log 10 (A)−1log 10 (R)−0.003R−1.963