Temporary Seismic Network in the Metropolitan Area of Rome (Italy): New Insight on an Urban Seismology Experiment

Abstract

This study presents data and preliminary analysis from a temporary seismic network (SPQR), which was deployed in the urban area of Rome (Italy) for three months in early 2021. The network was designed to investigate the city’s subsurface while evaluating the feasibility of a permanent urban seismic network, and consisted of 24 seismic stations. Despite significant anthropogenic noise, the SPQR network well recorded earthquake signals, revealing clear spatial variability referable to site effects. In addition, the network’s continuous recordings allowed the use of seismic noise and earthquake signals to derive spectral ratios at sites located in different geological and lithological settings. During the experiment, there were periods of activity restrictions imposed on citizens to limit the spread of COVID-19. Although the observed power spectral density levels at stations may not show visible noise reductions, they do cause variations in calculated spectral ratios across measurement sites. Finally, a statistical noise analysis was conducted on continuous seismic station data to evaluate their performance in terms of detection threshold for earthquakes. The results indicate that all network stations can effectively record earthquakes with a good signal-to-noise ratio (≥5 for P and S phases) in the magnitude range of 1.9–3.3 at distances of 10 km and 80 km, respectively. In addition, the network has the potential to record earthquakes of magnitude 4 up to 200 km, covering areas in Central Italy that are far from the city. This analysis shows that it is possible to establish urban observatories in noisy cities such as Rome, where hazard studies are of particular importance due to the high vulnerability (inherent fragility of its monumental heritage) and exposure.