Lower St. Lawrence Seaway Amphibious Seismic Network for earthquakes and marine soundscape monitoring

The Lower St. Lawrence Seaway (LSLS) is located within one of the most active seismic zones in eastern Canada. It is also home to a range of marine mammals in an environment of intensive fishing and cargo shipping. With the dual objectives to better understand the geohazards and marine soundscape, we operated along the LSLS an amphibious seismic network consisting of 8 broadband ocean bottom seismometers (OBS), 48 short-period nodal sensors, and 4 broadband land stations, with various operation periods between 2023 and 2025. This report documents the deployments, examines data quality, and presents preliminary results from the first month of OBS recording. The OBS recordings show higher noise levels across all frequencies compared to the land broadband stations, with particularly high noise between periods of 0.2-2 s and >10 s on the horizontal components. Long-period noise amplitude correlates closely with tidal cycles, suggesting tidally modulated riverbed currents are the primary cause. The seismicity catalog from combined OBS and land stations shows two times more earthquakes than the Canadian National Earthquake Database in the first month of deployment, as well as many suspected blasts. We also show clear detections of fin whale and blue whale calls at multiple OBS sites, illustrating the potential for whale call location.