Investigation of high-frequency (> 1Hz) ambient noise in seismic data recorded in very shallow, near-shore settings

Currently, several carbon capture and storage (CCS) projects in the North Sea region are underway. To verify a safe and permanent storage of CO₂ in the geological reservoir, passive seismic monitoring – based on sensors installed near the injection site – is a necessity. However, seismic sensors installed at or below the seabed in shallow waters are subject to considerable noise sources such as wind, collapsing whitecaps, waves rolling onto nearby beaches, bypassing vessels and currents. Here, we report analyses from a 3-months long broadband OBS deployment at 19 m water depth in the Baltic Sea. Parallel recordings of a nearby metocean station allow for a detailed discrimination of processes generating ambient seismic noise of frequencies above the well-known primary and secondary microseism peaks. The presented results are put into context of passive seismic monitoring at offshore CCS-projects.