Estimating the low-frequency seismic response of Submarine Fiber Optics with a teleseismic recording

Recently, with rapid developments in distributed acoustic sensing (DAS) techniques, optical fibers are widely used as seismometers to carry out dense and broadband seismic observation. However, the frequency responses, especially the low-frequency responses of submarine cables, which are of key importance in focal mechanism and deep seismic imaging, are still poorly understood. In this study, we comprehensively evaluated the phase and amplitude responses of the submarine DAS array by comparing teleseismic records from the DAS array and traditional broadband seismometers. Our 21 km long DAS array is located around 1,500 kilometres from the epicentre, and two fixed seismometers from the Shandong Provincial Seismic Network are positioned at either end of the array. Our results show that for phase response, the data from DAS and seismometers are of great similarity, with a cross-correlation coefficient reaching 80%. For amplitudes, the velocity value recorded by CHD (Shandong Provincial Seismic Network Changdao Seismic Station) seismometers is about 1.6 times the value obtained by DAS. In terms of surface wave dispersion, the differences between the different data sets are generally less than 3%. Our results verify the sensitivity of submarine optical fibers to low-frequency seismic signals and the feasibility of deep structure imaging using submarine DAS arrays.