ALBERT

Description: Ambient seismic noise is the component of the signal discarded in the procedures for interpreting the waveforms of earthquakes. The Signal / Noise ratio (S / N) is a parameter for assessing the quality of the seismic data in relation to the possibility of detecting the phases of earthquakes useful for their location. The signal is represented by the seismic event, which is a rare transient when seismic sequences are not in progress. Using high-performance seismic equipment, the noise is represented by the ambient seismic noise, which is detected in the form of vibrations imperceptible by humans. In cases where the dynamics of the instrument is restricted and its intrinsic noise is high, the seismic ambient noise cannot be detected, information relating to the medium crossed from the source to measurement point is lost and its variations cannot be revealed. Ambient seismic noise is a stochastic process from which stationary characteristics can be extracted, related to natural or anthropic sources that generally occur at different frequencies. Rapid vibrations with cycles below one second are well documented in the literature and are generally linked to anthropogenic activities, caused by industrial plants, domestic appliances, vehicular traffic and any transfer of energy to the ground that propagates seismic waves (Peterson, 1993; McNamara and Buland, 2004). The restrictive measures issued by the Italian Government in year 2020 due to the contagion from COVID-19 (http://www.governo.it/it/coronavirus-normativa) have significantly reduced the sources of cultural seismic noise that transmit seismic waves into the ground, which are not perceived by people but only detectable by seismic instruments. In Italy, the territory is monitored in real time and continuously by the National Seismic Network (RSN) of the National Institute of Geophysics and Volcanology (INGV Seismological Data Center, 2006). Some works show how it is possible to characterize the variability of seismic noise on the national territory, identifying the origin and nature of seismic waves of background vibrations (Marzorati and Bindi, 2006; Marzorati, 2007; Marzorati and Bindi, 2008; Li et al., 2010 ; Vassallo et al., 2012). This report shows the reduction of the average levels of seismic noise in the frequency range between 2 and 8 Hz, so as to be able to exclude natural sources at lower frequency and to analyze signals that have the ability to propagate at significant distances from the sources, in order to reach seismic stations located in large italian cities or in their surroundings. The seismic data of seismic stations of the RSN were analyzed by extracting the seismic noise values from the web services (INGVWS) of the National Earthquake Observatory (ONT) INGV (http://webservices.ingv.it).

Description: Istituto Nazionale di Geofisica e Vulcanologia

Description: Unpublished

Description: 4T. Sismicità dell'Italia