EGU24-10120, updated on 29 Mar 2024
https://doi.org/10.5194/egusphere-egu24-10120
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

An Earthquake Observatory based on Coherent Interferometry over the Optical Fiber Network in Italy

Simone Donadello1, Cecilia Clivati1, Aladino Govoni2, Lucia Margheriti2, Maurizio Vassallo3, Daniele Brenda4, Marianna Hovsepyan4, Elio Bertacco1, Roberto Concas1, Filippo Levi1, Alberto Mura1, Andrè Herrero3, Francesco Carpentieri4, and Davide Calonico1
Simone Donadello et al.
  • 1Istituto Nazionale di Ricerca Metrologica, Torino, Italy
  • 2Istituto Nazionale di Geofisica e Vulcanologia, ONT, Roma, Italy
  • 3Istituto Nazionale di Geofisica e Vulcanologia, Roma1, Roma, Italy
  • 4Open Fiber, Rome, Italy

Optical fiber sensing represents a promising technology for seismological monitoring, leveraging the widespread deployment of optical networks, and representing an important opportunity for the development of early warning systems. While so far Distributed Acoustic Sensing (DAS) has been widely employed in geosciences, this technology shows some limitations, like a restricted working range, requirement of dedicated fibers and criticalities in the management of big datasets. We focus on an alternative technique, coherent interferometry relying on ultrastable lasers, which is characterized by high sensitivity, long range, and full compatibility with the existing telecommunication infrastructure. The method allows detecting perturbations induced by seismic events through the measurement of the phase accumulated by an optical signal along the fiber path. The best performances are obtained employing narrow-linewidth lasers inherited from metrological applications due to their high coherence. While the technique was initially demonstrated on subsea cables, its application to on-land fibers poses new challenges. Indeed, the phase measurement integrates all the perturbations occurring along the fiber: this means that anthropic activities, such as vehicle traffic, represent important noise sources that must be taken into account. 

We present the details of an in-field implementation over a commercial fiber deployed in a highly seismic region in central Italy and connecting two populated towns. The experimental setup employs self-heterodyne interferometry detection, utilizing a continuous wave laser stabilized to an optical cavity through the Pound-Drever-Hall technique. The laser operates within a single channel of the Dense Wavelength Division Multiplexing (DWDM) grid, sharing the fiber with standard internet services. We show the results of continuous observations performed over a period of two years. We demonstrate the detection of about one hundred earthquakes, distinguishing them from typical noise sources such as acoustic interference and infrastructure oscillations. The results include the detection of both local and distant earthquakes, demonstrating the robustness of the technique. This allowed us to characterize for the first time the sensitivity curve of the technique, described by the probability of the event detection as a function of its magnitude and epicenter distance. We also show the correlation between the source magnitude and signal spectral analysis.

In conclusion, we present an operational fiber-based earthquake observatory, highlighting the compatibility of coherent interferometry with the existing telecommunication infrastructures and its effectiveness in seismic monitoring. The results are promising for the development of scalable sensing networks utilizing the extensive optical fiber infrastructure already in place, which can conveniently integrate in real-time the data acquired with the existing networks of classical seismological sensors.

How to cite: Donadello, S., Clivati, C., Govoni, A., Margheriti, L., Vassallo, M., Brenda, D., Hovsepyan, M., Bertacco, E., Concas, R., Levi, F., Mura, A., Herrero, A., Carpentieri, F., and Calonico, D.: An Earthquake Observatory based on Coherent Interferometry over the Optical Fiber Network in Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10120, https://doi.org/10.5194/egusphere-egu24-10120, 2024.