The 26 September 2022 Nord Stream Events: Insights from Nearby Seismic Events

On 26 September 2022, two seismic events were detected by regional seismic networks, coincident with media-reported leaks from the Nord Stream gas pipelines in the western Baltic Sea. In this study, we analyze seismic and infrasound signals from these two events and compare the seismic signals with those from other nearby seismic events such as underwater explosions and presumed earthquakes. Arrival times of seismic signals from the events on 26 September 2022 are used to show that the epicenters for both the events are in the vicinity of the Nord Stream pipelines. Signals from the two events display features that are characteristic of sources occurring near the seafloor. Observed P/S ratios from the Nord Stream events are also different from those observed for nearby presumed earthquakes. The observed seismic and infrasound signals are longer duration than would be expected from a single explosive source and show similarities with those observed from underwater volcano eruptions and gas pipeline explosions. The difference between seismic magnitudes estimated for the first Nord Stream pipeline event (MLP 2.32) and an event associated with the rupture of the Balticconnector pipeline on 7 October 2023 (MLP 1.09) is consistent with the estimated potential energy ratio of the gas in the pipelines. This suggests that the initial seismic signals from the first Nord Stream event may be dominated by energy generated by the venting of gas.