The catastrophic earthquakes that have occurred in Italy and around the world have taught us that rapid and precise information on the location of the epicenter and the magnitude of the seismic event is essential so that the Civil Protection can organize first aid in the affected areas.
Historically, the INGV monitoring network was born and took shape in the early 80s, following the Irpinia earthquake of November 23, 1980 (fig.1)
The figure shows a map of the RSNC, dating back to the early 90s. At the time, the network was exclusively of the analogue type and included about 70 stations with only vertical sensors with the exception of a few sites, where the 2 horizontal sensors were also mounted to obtain the complete motion of the ground.
At the time, the transmission of the seismic signal was entrusted to a system which provided for the use of purely analogical electronics: an amplifier of the signal coming from the sensor and a modulator for the transmission on the always active telephone line, which connected the remote station with the operations room in Rome, where the signals were demodulated and recorded.
At the time the seismic data were recorded on thermosensitive paper (seismograph) and the arrival times of the various seismic waves were read by hand (with a ruler from the seismograms) and manually loaded onto the epicentral calculation system.
Assuming that the time required for transmission from the various stations was practically nil or in any case irrelevant from the point of view of the location of the seismic events, the timing of the seismic signal took place directly in Rome, where the reception of the signals was associated with the "international ” initially generated by an atomic clock and later by a professional GPS.
Seismic trace digitization was implemented in the early 90s.
In the mid-90s, advances in technology brought about radical changes in both the acquisition and transmission and recording of RSN data. We pass from one-component sensors to three-component sensors and extend both the frequency band and the dynamics of the recorded signal, the acquisition systems pass from analog to digital, with the first 24-bit digital stations, the brand of the time it is associated with the seismic signal on site through a special GPS receiver and finally the transmission continues to be on telephone cable, but digital and no longer analogical.
The transition from analog to digital has brought a series of advantages, such as the elimination of the uncertainties and errors due to the transmission of the non-timed analog signal, the increase in dynamics from 60dbm to 130dbm and the perfect calibration of the signals and of the acquisition chain . It was consequently possible to define the Magnitude more precisely,
passing from the Magnitudo-Duration taken on the Paper Rolls to the far more reliable calculation of the Magnitudo-Gutenberg Richter, based on the reading of the amplitudes of the S waves.
Given the huge costs of digital data acquisition devices, at the end of the 90s the INGV laboratories designed and developed a data acquisition tool called GAIA, now in use on most of the RSN.
Alongside the telephone-type transmission vector, the first satellite connections appeared at the beginning of the 2000s and later also UMTS and WiFi. The differentiation of the transmission vectors increases the robustness of the RSN, no longer dependent on a single transmission system. Furthermore, accelerometer sensors and geodetic GPS were progressively combined with the seismic velocimetric sensor, giving way to what would become within a few years the modern and current multiparametric National Seismic Network.
To date, the National Seismic Network consists of about 500 stations scattered throughout the country, all teletransmitted to the INGV Seismic Room, where a 24-hour localization and evaluation service of the magnitude of seismic events that occur in Italy is in operation. in order to allow seismic monitoring of the national territory, one of the main institutional tasks of INGV.
Most of the stations are managed directly by the personnel of the various INGV offices, but thanks to the current communication possibilities provided by new technologies and the Internet, the RSN is enriched by the stations of various other Italian and foreign networks.
The following Organizations contribute to the RSN:
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the network of North Western Italy Lunigiana and Garfagnana, managed by the Department of Earth, Environmental and Life Sciences of the University of Genoa (DISTAV, network code GU);
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the broadband network of North Eastern Italy managed by the Seismological Research Center (CRS) of the National Institute of Oceanography and Experimental Geophysics (OGS-CRS, Network Code OX);
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the regional networks of Trentino (network code ST) and Alto Adige (network code SI);
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the network of the Marche Region;
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the Alta Val Tiberina network (TABOO project);
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the Lardarello network;
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the Irpinia network;
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the network of the University of Calabria.
The complete list of the stations of the National Seismic Network, managed by INGV and of the other regional and local networks managed by other Bodies is available on the page https://www.ont.ingv.it/monitoraggio-e-sorveglianza/la-rete-sismica-nazionale/sviluppo-della-rsn).
The Seismic Network is a constantly evolving structure, both the acquisition and transmission systems change and improve, the number of stations increases, backup systems are prepared to ensure both reception and archiving of data.
The constant technological developments implemented in recent years have brought about a significant improvement in monitoring, allowing on the one hand to significantly lower the network detection threshold and on the other to drastically reduce processing times for the complete usability of the information, both Civil Protection purposes, and for scientific research purposes.
To date, on most of the national territory we are able to locate events from magnitude 1 upwards, while in areas where the network is more sparse we are still able to determine seismic events from magnitude 2 upwards. There are also areas characterized by a higher density of stations, where our detection threshold is well below Magnitude 1.