GNGTS 2022 - Atti del 40° Convegno Nazionale

378 GNGTS 2022 Sessione 2.2 has mainly the objective of the seismic surveillance of the territory (i.e. earthquake locations) and the seismological studies, the latter network collects full records of strong earthquakes to understand the seismic activities under different geological conditions and it also serves as the basis for intensity assessment and to design the earthquake-resistant building codes. Insights about the degree of coverage of a seismic network in term can be provided counting the number of events at increasing distance from each seismic station. The plots in Fig. 1 (upper row) display the cumulative curves, one for each seismic stations, for the three countries. The steeper the curves, the better the position of the considered seismic station with respect to the local seismicity (distance shorter than 100 km). In all the three cases, many stations are clustered and follow the same increasing trend; other seismic stations are more scattered. In this diagram it is possible to distinguish which stations are optimally placed (i.e. high number of earthquakes recorded at short distance) from the bad placed stations Tab. 1 - Comparison of characteristics of the earthquake monitoring networks of each country and details of the earthquake catalogues. Italy New Zealand Taiwan Surface area (km 2 ) 300*10 3 268*10 3 36*10 3 N. seismic stations 604 562 278 Density seismic stations (n/km 2 ) 1.99*10 -3 2.10*10 -3 7.68*10 -3 N. strong-motion stations 647 363 716 Density strong-motion stations (n/km 2 ) 2.14*10 -3 1.35*10 -3 19.78*10 -3 N. instrumental earthquakes M>3 1172 101761 9235 N. earthquakes M>5 79 328 287 Average population density (people/km 2 ) 189 18 583 Fig. 2 - Top row: cumulative number of instrumental earthquakes located at increasing distance from each seismic station. Bottom row: cumulative seismic moment of events M>=5 (either measured or estimated for historical earthquakes) located at increasing distance from each strong motion station.