Sound characterization and marine mammal impact assessment of a marine vibroseis source in a shallow, near-shore environment

Marine vibroseis offers an alternative to airguns for oil and gas exploration in the marine environment that is expected to be less impactful to marine life because the emitted noise is of lower amplitude and of limited bandwidth at very low frequencies. Underwater noise from a marine vibroseis source (SAExploration) was measured in a shallow, near-shore region of Cook Inlet, AK, during a pilot study by Hilcorp Alaska, LLC. Two signals were measured, a 48-s low-frequency sweep between 1.5 and 16 Hz and a 16.4-s high-frequency sweep between 8 and 96 Hz. Source level estimates were 183 and 192 dB re 1 μPa2m2 for the low- and high-frequency sweeps, respectively. Received sound levels were analyzed to estimate the distances from the source to U.S. regulatory thresholds for the onset of acoustic injury and behavioral disturbance. Calculations predicted that sound levels reached thresholds for behavioral disturbance at ranges between 10 m and 2.4 km, depending on the criteria used to assess this potential effect, and never reached thresholds for acoustic injury onset. Potential for marine mammal impacts due to noise from this source in coastal Cook Inlet, AK is expected to be reduced compared to the potential impacts from airgun noise.