The Loudest Sound on the Planet: Airgun Blasts and Impacts of Seismic Imaging Technology

(Note: following the denial of PG&E’s permit application by the Coastal Commission on Nov 14, 2012, high intensity acoustic seismic testing is off the table for 2012 for the San Luis Obispo County coast.  However, so-called low-intensity testing with sound intensity levels reaching above 200 decibels is still permitted, and high intensity projects with decibel levels reaching 240-260 are still proposed elsewhere along the California coast and northwards, as well as along the entire Atlantic coast of the U.S.)

The airguns used for PG&E’s proposed acoustic seismic testing project will emit blasts that will be among the loudest sounds that can be created on the planet.  Literally.  No exaggeration.  The sound intensity level of the airgun blasts will be 230 to 252 decibels at the source.  For comparison, a seafloor volcanic eruption has a sound intensity of 255 decibels, at a distance of 3 feet, and a lightening strike on the ocean surface would be 260 decibels.

However, unlike most natural events which occur suddenly and then end quickly, during PG&E’s high-intensity seismic imaging project the airguns will continue to blast every 15 seconds, 24-hours a day, for days on end, week after week, until the project is complete.  The blasting will be unrelenting.  For living ocean residents, there will be no relief.  For those unfortunate enough to be in close proximity to the ship, results will likely be fatal, either immediately, or more slowly as a result of injury, displacement or disorientation.  Impacts may be immediate and dramatic to large marine mammals such as whales and dolphins and sea lions and sea otters, with carcasses washing ashore that can be counted and tabulated.  Or impacts may be more subtle and delayed, more difficult to measure, appearing over the course of years as decreased catches in commercial fisheries and declines in local marine populations. 

Take a look at the references below, and other pages on this website, for further information about the impacts of manmade sound on the underwater environment and its inhabitants, the nature and effects of seismic testing, and PG&E’s own estimates of potential impacts on marine mammals from the hi-intensity seismic imaging project.

A frustratingly recurring conclusion in many of the reports on impacts of acoustic seismic testing on marine life (such as the Environmental Impact Statement for marine seismic research funded by the National Science Foundation and USGS)  is some version of the following: “There is insufficient data to be certain of effects of marine seismic testing on (fill-in-the-blank organism), but effects are not considered likely to be significant at a population level.” In other words, there hasn’t been enough research to really know whether or not harm is done, or how bad the harm will be, but we don’t believe the harm will be bad enough to completely drive the species to extinction.  Therefore, “impacts are considered less than significant at a population level.” 

As an example, PG&E’s EIR for the proposed offshore high energy acoustic seismic imaging project acknowledges that impacts to the California sea lion population may be locally significant, resulting in injury or mortality to between 500 to 800 individual sea lions.  But because the sea lion population is healthy along the California coast as a whole, the EIR ultimately dismisses the impacts on the California sea lion as less than significant, because the project would not endanger the survival of the population as a whole. 

However, here on the central coast, we would have 500-800 injured or dead sea lions.  According to PG&E’s own EIR estimates.

This is one example among many.   Research data is lacking regarding potential impacts of seismic testing to marine fisheries, invertebrates, rockfish, migrating salmonids, sea otters, etc. 

The risks are great.  The benefits are questionable.  There are alternatives.


Impacts to Marine Mammals from PG&E’s Proposed Hi-Intensity Seismic Imaging Project: Harassment/Injury/Mortality – Chart

Marine Mammal Ocean Acoustics Primer (link to pdf)

Decibels and sound underwater

Ocean Sounds – natural and manmade

Discovery of Sound in the Sea

Marine Mammal Commission 2007 Report to Congress “Marine Mammals and Noise” (pdf)

National Oceanic and Atmospheric Administration (NOAA) Marine Mammal Acoustic Guidelines

“Boom, Baby, Boom: The Environmental Impacts of Seismic Surveys” by the Natural Resources Defense Council (pdf)

Final Programmatic Environmental Impact Statement/ Overseas Environmental Impact Statement for Marine Seismic Research Funded by the National Science Foundation or Conducted by the U.S. Geological Survey (pdf)

Ocean Noise and Marine Mammals” by the National Research Council

Report of the Workshop on Acoustic Resonance as a Source of Tissue Trauma in Cetaceans. April 24 and 25, 2002, Silver Spring, MD (pdf)

 “Comments on the Central Coastal Seismic Imaging Project Draft Environmental Impact Report” from SLOSEA at the Cal Poly Center for Coastal Marine Sciences  (pdf)

 “A Review of the Impacts of Seismic Airgun Surveys on Marine Life” by Dr. Lindy Weilgart (Letter to California State Land Commission, August 14, 2012)

“Underestimating the damage: interpreting cetacean carcass recoveries in the context of the Deepwater Horizon/BP incident.”  Williams, R., S. Gero, L. Bejder, J. Calambokidis, S.D. Kraus, D. Lusseau, A.J. Read, and J Robbins. 2011. Conservation Letters.

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