The effect of confinement due to COVID-19 on seismic noise in Mexico

Abstract

Abstract. The world experienced the beginning of the COVID-19 pandemic by\nthe end of 2019 to the beginning of 2020. Governments implemented strategies to\ncontain it, most based on lockdowns. Mexico was no exception. The\nlockdown was initiated in March 2020, and with it, a reduction in the seismic\nnoise level was witnessed by the seismic stations of the national and\nValley of Mexico networks. Stations located in municipalities with more than\n50\u2009000 people usually experience larger seismic noise levels at frequencies\nbetween 1 and 5\u2009Hz, associated with human activity. The largest noise levels\nare recorded in Mexico City, which has the largest population in the country. The\nlargest drop was observed in Hermosillo, Sonora; however, it was also the\ncity with the fastest return to activities, which seems to correlate with a\nquick increase in confirmed COVID-19 cases. Mexico initiated a traffic-light\nsystem to modulate the re-opening of economic activities for each state.\nTherefore, since 1 June, noise levels have generally reflected the colour of the\nstate traffic light. Furthermore, the reduction in the noise level at\nseismic stations has allowed identification of smaller earthquakes without\nsignal processing. Also, people in cities have perceived smaller or more distant\nquakes.