GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 2.1 GNGTS 2024 The new version of the Foreshock Traffic Light System L. Gulia 1* , S. Wiemer 2 , E. Biondini 1 , G. Vannucci 3 , B. Enescu 4 1 University of Bologna, Department of Physics and Astronomy, Bologna, Italy 2 Swiss Seismological Service, ETH Zurich, Zurich, Switzerland 3 Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy 4 University of Kyoto, Kyoto, Japan After the occurrence of a moderate to large earthquake, the question shared between Civil Protection, scientists, the population, and all decision makers is only one: Was it the mainshock or a bigger event has yet to come? According to standard earthquake statistics, the chance that after a moderate earthquake an even larger event will occur within five days and 10 km is typically 5% (Reasenberg and Jones, 1990). Recently, a more specific answer to this question has been given by the Foreshock Traffic Light System (FTLS, Gulia and Wiemer, 2019). The method allows the real-time discrimination between foreshocks and aftershocks in well-monitored regions. However, some expert judgements are required in order to overcome local peculiarities (Brodsky, 2019) such as magnitude of completeness and the duration of the short-term aftershock incompleteness (STAI; Kagan, 2004). We here introduce and test the new version of the code that, using the b-positive estimator (van der Elst, 2021), successfully overcomes the above-mentioned limits, allowing the implementation of the FTLS already in few hours after a M ≥ 6 event without any specific expert judgements. References Brodsky, E. (2019). Predicting if the worst earthquake has passed. Nature, 574, 185-186. Gulia, L., and S. Wiemer (2019). Real-time discrimination of earthquake foreshocks and aftershocks, Nature 574, 193–199. Kagan, Y. Y. (2004). Short-term properties of earthquake catalogs and models of earthquake source. Bull. Seism. Soc. Am., 94(4), 1207–1228. https://doi.org/10.1785/012003098 van der Elst, N. J. (2021). B-positive: A robust estimator of aftershock magnitude distribution in transiently incomplete catalogs. J. Geophys. Res. Solid Earth, 126, e2020JB021027. https://doi.org/10.1029/2020JB021027