The Seismic Telemetry Network of the Strait of Messina: From Analog to Digital

The history of the Seismic Telemetry Network of the Geophysical and Geodetic Institute of the University of Messina represents one of the most significant examples of technological evolution applied to seismic monitoring in Italy. The network took shape between the late 1970s and the early 1980s, at a moment when advances in microelectronics allowed researchers to overcome the traditional model of the monolithic seismograph and to develop systems in which sensors distributed across the territory were telemetrically linked to a central recording facility.
A crucial turning point was the adoption of electromagnetic velocity sensors, such as the Willmore MKIII, which replaced earlier mechanical pendulum instruments. These single-degree-of-freedom transducers, sensitive to one direction of ground motion, formed the basis of the first peripheral stations installed in Messina, Ganzirri, Tremestieri, Martino, and Cannitello. The seismic signals they generated were converted into an audible-frequency subcarrier modulated in frequency, which could then be transmitted via UHF radio to the central observatory. The need to install stations on rocky outcrops, far from anthropogenic noise and with direct radio visibility to the institute, highlights the engineering precision required to build a fully analog telemetry network. The recording system, centred on the sophisticated Racal Geostore 14-track magnetic recorder, ensured exceptional stability and accuracy. Reduced wow and flutter, together with built-in electronic and mechanical compensation systems, allowed faithful reproduction of the seismic signal. Battery-buffered operation permitted extended autonomy in the absence of mains power. The signals recorded on magnetic tape were later demodulated and transferred onto paper by high-resolution oscillographs, enabling the precise temporal analyses needed for epicentral localisation. During this period, time synchronisation was ensured by the DCF77 radio signal, derived from a cesium standard, which aligned the time bases of all Italian and many European seismic networks.
Starting in the mid-1980s, the network underwent a profound transformation towards digital technologies. The first step was the introduction of a LeCroy analog-to-digital converter, interfaced with an IBM AT computer. Digitisation of the telemetered analog signals made it possible to create hard-disk archives and to perform amplitude- and frequency-domain analyses that had been impossible in the fully analog system. In parallel, the number of stations expanded to eleven, extending coverage across Messina, Reggio Calabria and the Aspromonte. The new digital stations hosted three-component seismometers oriented along the vertical, north–south, and east–west axes, greatly improving sensitivity and precision.
During the 1990s, the network reached its most advanced configuration, as summarised in the block diagram presented in the documentation: an integrated system incorporating radio transmission, local digitisation, continuous DCF77 synchronisation, and centralised recording on hard disk with a modified video recorder as backup. The network, known as the RSSM, became a national reference model for robustness, autonomy, and operational continuity. In the early 2000s, the centralisation of seismic data acquisition by the National Institute of Geophysics and Volcanology (INGV) made the maintenance of local networks increasingly difficult, and the RSSM was progressively decommissioned in 2003.
Today, the RSSM stands as a crucial testament to the evolution of Italian instrumental seismology: a cultural and technological transition that carried the field from mechanical analog systems to digital recording, anticipating the architecture of modern seismic monitoring networks.

___ Antonino Marino, Domenica De Domenico, Maria Teresa Caccamo, Salvatore Magazù