3rd EUROPEAN CONFERENCE ON EARTHQUAKE ENGINEERING & SEISMOLOGY BUCHAREST, ROMANIA, 2022 Non-extensive statistical physics analysis of high-frequency anthropogenic seismic noise with relation to COVID-19 pandemic lockdown measures: Preliminary observations Dimitrios Giannopoulos - Institute of Physics of the Earth’s Interior and Geohazards, UNESCO Chair on Solid Earth Physics and Geohazards Risk Reduction, Hellenic Mediterranean University Research Center (HMURC), 3 Romanou str., 73133, Chania, Crete, Greece. e-mail: dgiannopoulos@hmu.gr Filippos Vallianatos– Institute of Physics of the Earth’s Interior and Geohazards, UNESCO Chair on Solid Earth Physics and Geohazards Risk Reduction, Hellenic Mediterranean University Research Center (HMURC), 3 Romanou str., 73133, Chania, Crete, Greece. Section of Geophysics - Geothermics, Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, 157 84 Panepistimiopolis, Athens, Greece, e-mail: fvallian@geol.uoa.gr Athanasios Lois - Institute of Physics of the Earth’s Interior and Geohazards, UNESCO Chair on Solid Earth Physics and Geohazards Risk Reduction, Hellenic Mediterranean University Research Center (HMURC), 3 Romanou str., 73133, Chania, Crete, Greece, email: thlois@uniwa.gr George Hloupis - Institute of Physics of the Earth’s Interior and Geohazards, UNESCO Chair on Solid Earth Physics and Geohazards Risk Reduction, Hellenic Mediterranean University Research Center (HMURC), 3 Romanou str., 73133, Chania, Crete, Greece Department of Surveying and Geoinformatics Engineering, University of West Attica, Egaleo Campus, 12244 Athens, Greece. e-mail: hloupis@uniwa.gr Abstract: The pandemic of COVID-19 and the global policy implemented to attenuate the spread of the virus, provided a unique opportunity to study the footprint of the resulting social impact of COVID-19 pandemic on seismic data. In this study, a non-extensive statistical physics approach is examined for anthropogenic high-frequency seismic noise in view of COVID-19 pandemic lockdown measures and the consequent changes in human activity levels. A continuous monitoring of the entropic index q performed during a time period which includes a time interval of normal social activity and a period of anthropogenic quiescence due to the COVID-19 pandemic lockdown measures, enabled us to observe a dependance between the human activity levels and the degree of non-extensivity in the seismic signal. Average values of pre-lockdown q parameters estimated within the urban environment of the cities of Athens and Thessaloniki (Greece), were equal to 1.37 and 1.56, respectively, while the respective post-lockdown q values were found to be 1.25 and 1.49. In overall, the estimated q parameters could support the conclusion that the anthropogenic seismic noise is sub-extensive. Lower values of q during the lockdown period reflect a lower degree of interacting subsystems and degree of correlations in the high-frequency seismic noise wavefield. A short-term examination on a week scale of the temporal behavior of parameter q, revealed significant patterns of daily periodicity and diurnal variations resembling the diurnal cycle of human activities. According to the preliminary observations of this study, the non-extensive parameter q is shown to be a rather promising tool regarding the quantitative strategies for monitoring the effect of the anthropogenic activity levels in seismic data. Keywords: Tsallis entropy, non-extensive statistics, ambient seismic noise, seismic noise monitoring, Covid-19, Greece 1. Introduction The first human cases of the disease caused by the coronavirus SARS-CoV-2, officially abbreviated as COVID-19 by the World Health Organization (WHO), were first reported in China, in December 2019 (Zhu et al. 2020). As the virus was rapidly spreading throughout the world, WHO formally declared the COVID-19 outbreak a pandemic in 5161 3ECEES, September 2022, Bucharest, Romania