Irpinia: from experimentation to new seismic monitoring system with fiber optics

The Irpinia Near Fault Observatory (INFO), the observing system for the study of seismicity in Irpinia born from the collaboration between theNational Institute of Geophysics and Volcanology (INGV) and theUniversity of Naples Federico II, as part of the European research infrastructure EPOS, becomes an operational reality thanks to the INGV PNRR-MEET Project.

For more than a year now, the INFO observatory has been equipped with an experimental distributed seismic sensing (DAS) device, implemented in Tito Scalo (PZ), and based on 20 km of optical fiber. To date, seismic signal acquisition is extended to an 80-km stretch of fiber optics, constituting a continuous monitoring system of the Irpinia-Lucania fault system that connects Sant'Angelo le Fratte to Castelgrande (PZ) and is capable of "photographing" subsurface movements with very high precision.

"If we look at the seismicity in Irpinia in the last 20 years," notes Giulio Selvaggi, INGV seismologist and scientific coordinator of the MEET project, " there are few seismic events of significant magnitude. In order to be able to study the fault system and understand the dynamics of the Earth's crust in the area, we need a magnifying glass that allows us to see the smallest earthquakes and analyze them in detail."

Through a collaboration with the companies Metis and Fastweb, fiber optics commonly used for telecommunications are now being deployed as a dense network of sensors distributed along the route.

"The measurements come from a laser source that sends light pulses inside the fiber," explains Gilberto Saccorotti, seismologist at INGV. "The passage of the seismic wave deforms the fiber and, by modifying the optical path of the pulses, allows us to accurately measure ground deformation. It is like having a seismometer installed every 10 meters, along a distance of 80 km."

The new system, dedicated to characterizing microseismicity in the area, has already recorded numerous low-magnitude events. However, by continuously monitoring the Irpinia-Lucano fault system, it was also able to record the ML 4.0 magnitude earthquake that occurred in the Montefredane (AV) area last Oct. 25, at a depth of about 15 km. The ground deformation caused by this event was observed along the entire 80 km of optical fiber, providing a detailed and continuous image of seismic wave propagation that is currently unprecedented on a national scale.

"We are in front of a real new monitoring system that radically transforms the signal that until now we were able to detect with traditional seismic sensors," concludes Gaetano Festa, professor of Physics at the University of Naples Federico II. " With 80 km of cable integrated with the DAS, we are able to characterize in detail even the microseismicity and make a quantum leap in the knowledge of the processes occurring on the fault system of Irpinia and seismic risk.

A technological leap that marks a decisive advance in the ability to closely observe the genesis and dynamics of earthquakes, paving the way for new applications of fiber optics in Italian geophysics.