Seismic monitoring of the October 2023 storm surge along the coast of the Baltic Sea

The coupling between ocean and seismic waves – often referred to as (oceanic) microseism – is a well-established concept since the 1950’s. Ocean and seismic waves are correlating not only on seasonal to annual, but also on daily timescales, in particular during extreme weather events. The most prominent microseism signals have periods below ten seconds and originate from interfering water waves. They are called secondary microseism and can be related to marine storm activity. While some secondary microseism may arrive from far-away coastal regions, a strong contribution also results from nearby coastal wave activity. This paper shows that measurements of microseism from our recently expended seismic network in northern Germany are well suited to monitor wave propagation processes in coastal areas during extreme weather events like the October 2023 storm surge. We utilize three component seismic data from seven stations along the German Baltic Sea coastline and infrasound data from the local array Kühlungsborn (IKUDE) to investigate secondary microseism and atmospheric pressure variations during the storm surge. Spectral investigations over time show distinct local differences in secondary microseism of the Baltic Sea at three different near coastal sites which correlate with half the peak wave period in each respective area. Infrasound measurements reveal additional noise sources, such as nearby wind parks, anthropogenic sources or microbaroms in the North Atlantic and probably the North Sea which are transferred through the atmosphere and absent in seismic data and vice versa. Therefore, sources of our seismic measurements during the October 2023 storm surge are related rather to ocean generated microseism, transferred through the solid Earth than to atmospheric pressure sources. As amplitudes related to secondary microseism of the Baltic Sea decrease with increasing distance of the station to the coast, this allows for an estimation of a sensitivity range along the Baltic Sea coastline. For seismic monitoring of coastal areas, seismic stations are needed to be within 25−30 km distance to the coastline to precisely detect locally generated microseism.