Explosive yield estimates for shallow water explosions from moment magnitudes

The explosive yield- seismic magnitude relation of shallow submarine explosions are not well confined. Local agencies often use local seismic magnitude, such as the traditional richter scale, which are often not calibrated for submarine environments. The importance of an estimated explosive yield in TnT equivalent becomes obvious when security concerns arise. After the North Stream events a number of very differing magnitude were presented by several seismological surveys and therefore the related yield estimates varied a lot. This lead to derived estimates ranging from tens of kg to hundreds of kg TnT equivalent explosive used in the North Stream explosions, giving different plausible scenarios for potential perpetrators.

We present an relatively simple and fast approach to use the comparison of recorded and forward modelled envelope and cepstral information to derive the moment magnitude of several large and small submarine explosion in the Baltic sea. Moment magnitudes are more robust in comparison to local magnitudes. We asses the performance of this approach by relating the moment magnitudes to yield estimates from known explosive events.  We use events from the Baltic sea, including events from offshore Bornholm from September 2025 with around 400kg TnT yield, recorded at local and regional distances up to 500km.

Infrasound recordings of stations in Germany are in good correlation with the seismic recordings, showing the possibility of combined energy release estimates. The strong importance of the source depth and shallow submarine geology is highlighted by the modelling results, providing still a large uncertainty range for unknown sources. We do find in general a good agreement between the estimated yield and actual yield for the known sources.