GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.1 5 HOW TO ESTIMATE THE RELIABILITY OF MICRO-EARTHQUAKE FAULT PLANE SOLUTIONS? G.M. Adinolfi 1,3 , R. De Matteis 1 , R. de Nardis 2,3 , A. Zollo 4 1 Dipartimento di Scienze e Tecnologie, Università degli Studi del Sannio, Benevento, Italy 2 Dipartimento di Scienze Psicologiche, della Salute e del Territorio, Università di Chieti-Pescara “G. d’Annunzio”, Chieti, Italy 3 CRUST Centro inteRUniversitario per l’analisi SismoTettonica tridimensionale, Chieti, Italy 4 Dipartimento di Fisica, Università di Napoli “Federico II”, Complesso Universitario di Monte S.Angelo, Napoli, Italy Earthquake focalmechanisms provideprimary informationon the kinematics of seismogenic faults and on the stress regime acting in a region. In the case of micro-seismicity monitoring, the source characterization is the most powerful tool for obtaining information on the fault structures, their stress level and for monitoring space-time evolution of seismicity due to natural or human-induced stresses. Despite the existence of several techniques operating in specific magnitude ranges, both in the time and frequency domain using different data as inputs (e.g., P polarities, S-wave polarization, S/P-amplitude ratios, etc.), the estimation of fault plane solutions can be a challenge when small magnitude earthquakes are analysed. The limited number of available data, the higher noise level or the weak knowledge of crustal structure at the wavelengths at which microearthquakes radiate severely affect the reliability of the focal mechanism solutions increasing their relative uncertainties. In this work, we propose a useful methodology, as described in Adinolfi et al. (2022), to evaluate the reliability of earthquake focal mechanism as a function of magnitude, location, and kinematics of seismic source, using a Bayesian approach that jointly inverts the P/S long- period spectral-level ratios and the P polarities to infer the solution (De Matteis et al. ; 2016). Additionally, from a theoretical point of view, we explore the capability of seismic networks, in terms of number and geographical location of stations, to constrain fault plane solutions of earthquakes taking into account the solution uncertainties. Hence, the proposed tool can be used with a double purpose: 1) to test the performance of local seismic networks to recover fault plane solutions and 2) to estimate the uncertainty of focal mechanism solutions when it is unavailable or not provided by other techniques. We validate our methodology by computing synthetic data and testing the performance of the Irpinia Seismic Network, a local seismic network operating in the Campania–Lucania Apennines (Southern Italy) aimed to monitor the complex normal fault system activated during the M s 6.9, 1980 earthquake. We prove the effectiveness of the proposed tool which can be easily customized for other case studies or network geometries. References Adinolfi, G. M., De Matteis, R., de Nardis, R., and Zollo, A.: A functional tool to explore the reliability of micro- earthquake focal mechanism solutions for seismotectonic purposes, Solid Earth, 13, 65–83, https://doi. org/10.5194/se-13-65-2022, 2022. De Matteis, R., Convertito, V., and Zollo, A.: BISTROP: Bayesian inversion of spectral-level ratios and P-wave polarities for focal mechanism determination, Seismol. Res. Lett., 87, 944–954, https://doi.org/10.1785/0220150259, 2016.