Experience in Earthquake Detection with a Distributed Fiber Optic Acoustic Sensor (DAS) Deployed on the Bottom of the Black Sea from August 25 to November 30, 2021

The practical results of earthquake detection with a distributed acoustic sensor (DAS) developed by PetroFibre LLC are reported. The operating principle of the DAS is based on interferometric detection of light resulting from Rayleigh scattering in optical fibers. The detected earthquake occurred in Iran. A fiber optic cable used as the sensitive element of the DAS was placed at the bottom of a shallow water region of the Black Sea, supervised by the Southern Branch of the Shirshov Institute of Oceanology, Russian Academy of Sciences. Gravity waves are shown to be a significant interference factor, preventing analysis of the wavefield for seismic event detection. Filtering the wavefield with a lower cutoff frequency exceeding 0.05 Hz was used to suppress the influence of the gravity waves. The specific features of the directivity pattern of the fiber optic cable as a sensitive element are considered; results are given indicating a lack of susceptibility of the cable to acoustic perturbations acting on it transversally.