Seismic events detection through the REFIMEVE optical fiber network

In the past few years, many new developments have demonstrated the possibility of using long-distance optical fiber links as a vast distributed network of sensors for environmental detection, and more specifically for earthquake detection [e.g, 1-2]. In fact, the mechanical and physical properties of the optical fiber and the light waves propagating inside it are sensitives to the mechanical stresses and external disturbances, respectively, such as the seismic waves [e.g; 3]. In France and through the ultra-stable frequency signal developed in the SYRTE and the spiderweb configuration of the French national metrological network REFIMEVE (REseau FIbré MEtrologique à Vocation Européenne), several seismic events were detected on the optical fibers since 2015.   We would like to propose a statistical analysis of the last three years' records, focusing on seismic events of magnitude > 6 around the globe. In this work, we narrowed our study on 3 long-distance links (between 200 – 600 km), where we explored the similarities and differences of the seismic records properties among the 3 links. Our investigation showed that we do not detect systematically all the selected seismic events on the REFIMEVE network.  However, we observed that the higher number of seismic event detection was made on the longer optical fiber link (Paris-Lyon; 600 km length). To highlight the difference between the observed and not observed seismic events on REFIMEVE network, we first explored the noise level effect. The results showed that the noise is quasi-stable and that the variability of the noise level is so insignificant that it is insufficient to explain the difference between observed and unobserved events. Then, we explored the different seismic source parameters (such as the epicentral distance, the depth, the focal mechanisms, the magnitude). At this time, our results do not show clear pattern between the source parameters that could explain the difference between the observed and not observed seismic events. However, we would like to present the first catalogs of seismic events that we have been able to build on our observations of the various links.        [1] D. C. Bowden et al., Geophysical Research Letters (2022) doi: 10.1029/2022GL098727. [2] E. Ip et al., in Optical Fiber Communication Conference (OFC) 2022  (2022) https://ieeexplore.ieee.org/document/9748358 [3] A. Trabattoni et al., Geophysical Journal International (2023),  https://doi.org/10.1093/gji/ggad365