Acoustic Measurements During a Seismic Airgun Survey: The Case of the Cascadia Subduction Zone

Results are presented from a recently concluded field effort to understand the effect of acoustic particle motion levels from a geophysical seismic survey on rockfish, lingcod, and Dungeness crab located within the Redfish Rocks Marine Reserve near Port Orford, Oregon. The study was conducted in summer 2021 during a 40-day geophysical seismic survey along the Cascadia Subduction Zone offshore of Oregon and Washington. The study collected measurements of acoustic pressure and particle motion, accompanied by in situ tagging of the aforementioned species. Presented in this chapter are a characterization of the acoustic fields that can potentially drive observed behavioral responses of the tagged species. The noise floor during the study period was strongly dominated by wind noise, with occasional contributions from small boat traffic. During the seismic surveys, received peak pressure levels were found to exceed 160 dB re 1 μPa (corresponding to peak measured particle velocity levels of 95 dB re 1 nm/s) when the seismic sound source was at a distance of 30 km from the vector sensor array. In contrast, band-averaged ambient pressure levels were in the 100–120 dB re 1 μPa range (corresponding to particle velocity levels that were in the 60 dB re 1 nm/s range).