Stanislav Glubokovskikh, Roman Pevzner , Evgenii Sidenko , Konstantin Tertyshnikov, Boris Gurevich , Sergey Shatalin , Alexey Slunyaev, Efim Pelinovsky 

Ocean-generated seismic waves are omnipresent in passive seismic records around the world and present both a challenge for earthquakes observations and an input signal for interferometric methods for characterisation of the Earth's interior. Understanding of these waves requires the knowledge of the depth-dependence of the oceanic noise at the transition into continent. To this end, we examine 80 days of continuous acquisition with Distributed Acoustic Sensor (DAS) system deployed in two deep boreholes near the south-eastern coast of Australia. The data has excellent Signal-to-Noise Ratio (SNR) in a range from 0.03Hz to over 100Hz. By analysing the seismograms and correlation with wave climate, the DAS response are confidently decomposed into the microseisms generated by swell from remote storms (~0.15Hz) and local winds (between 0.3Hz and 2Hz), and strong body waves energy from large surf break at the coast (from 2Hz to 20Hz). The depth dependence of the microseims allows for robust normal modes analysis of the Rayleigh waves with only one borehole. The results of this analysis agree with the data from conventional dense seismological arrays. Overall, we found that the link between the amplitudes at each channel along the borehole and wave climate is so strong and stable that with sufficient amount of training data, the passive seismic records on downhole DAS may be used for high-precision monitoring of both formations surrounding the borehole and remote storms in the ocean.