Fast M W estimation of microearthquakes recorded around the underground gas storage in the Montello-Collalto area (South
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ORIGINAL ARTICLE
Fast MW estimation of microearthquakes recorded around the underground gas storage in the Montello-Collalto area (Southeastern Alps, Italy) Alessandra Lanzoni & Luca Moratto & Enrico Priolo & Maria Adelaide Romano
Received: 12 April 2019 / Accepted: 29 October 2019 # The Author(s) 2019
Abstract Underground fluid injection and extraction is able to change pore fluid pressure at depth and make faults unstable, due to friction-force reduction, with an increased possibility of triggering earthquakes. Studying the local seismicity, down to microearthquakes, and stress field in areas where such activities are developed are essential steps to discriminate between natural and induced events. In this context, the moment magnitude (MW) is a key-parameter to both evaluate the energy balance and the stress involved in earthquake rupture process and assess seismic hazard accurately. Here, we focus on the fast MW estimation of microearthquakes recorded around the underground gas storage of Collalto (Northeastern Italy) by a dedicated seismic monitoring network. The area of Montello-Collalto, where this industrial activity is carried out, is densely populated and characterized by relevant seismic hazard. We compute MW from the response spectra (SA) calculated at fixed periods (i.e., 1.0 and 0.3 s); we show that log (SA) and MW scale as 2/3 and extend our method to microseismicity by using response spectra at 0.1 s. We eventually estimate MW for 1659 events (0.4 ≤ MW ≤ 3.5) and find that ML and MW scale as 2/3 too. The discrepancy between these two magnitude scales affects both the Gutenberg-Richter parameters and completeness A. Lanzoni : L. Moratto (*) : E. Priolo : M. A. Romano Istituto Nazionale di Oceanografia e di Geofisica Sperimentale OGS, Trieste, Italy e-mail: [email protected] A. Lanzoni Università di Trieste, Trieste, Italy
magnitude estimations; therefore, it has consequences when those quantities are used for physical interpretation. Our procedure shows to be efficient and suitable to be implemented within standard routine analyses of real-time monitoring and feed decision-making processes about plant management, such as the traffic light protocols. Keywords Underground gas storage (UGS) . Moment magnitude (MW) . Southeastern Alps (Northeastern Italy) . Seismic moment (M0) . Response spectra . Induced seismicity
1 Introduction The estimation of the moment magnitude MW and the related seismic moment M0 (Hanks and Kanamori 1979) is a fundamental task for investigating the dynamics of the earthquake source process, as M0 is directly associated with the fault rupture area and, indirectly, to the forces that cause it. At the same time, MW is preferred to ML in the probabilistic seismic hazard assessments, both for natural and induced earthquakes. Indeed, unlike ML, MW is not affected by saturation, anelastic attenuation, or scattering problems, and therefore, the fault to rupture provides more reliable estimations of the Gutenberg-Richter parameters (a and b values) (Edwards 2015; Staudenmaier et al.
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