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Cook Inletkeeper
Oil &
Gas/Seismic testing
BACKGROUND
Oil and gas corporations often rely on seismic surveys to
identify the location and extent of oil and gas reservoirs
beneath the seafloor. Historically, these seismic tests relied
on underwater explosive detonations, where ship-board sensors
would record the refraction of acoustic waves off the seafloor
to gauge reservoir location, size and depth. Today, most
seismic exploration work relies on large vessels that tow an
array of powerful air guns; these acoustic arrays fire
high-powered air blasts at short (e.g., 15 second) intervals to
help create a picture of underwater geological formations.
Seismic testing has been described as the loudest underwater
noise short of warfare. The intensity of sound waves produced
by the firing of seismic air guns can reach up to 250 decibels
(dB) near the source and can be as high as 117 dB over 20 miles
away. The sound intensity produced by a jackhammer is around 120
dB, which can damage human ears in as little as 15 seconds.
Various studies have shown adverse impacts to fish, marine
mammals and crabs from oil and gas seismic operations.
A
typical seismic survey lasts 2–3 weeks and covers a range of
about 300–600 miles. The intensity of sound waves produced by
the firing of seismic air guns can reach up to 250 decibels (dB)
near the source and can be as high as 117 dB over 20 miles away.
The sound intensity produced by a jackhammer is around 120 dB,
which can damage human ears in as little as 15 seconds.
What impacts can seismic surveys have on marine mammals?
Unlike humans and other terrestrial animals, marine mammals rely
on sound instead of sight as their primary sense. Dolphins,
whales and seals utilize their sense of hearing to locate prey,
avoid predators, choose migration routes, and to communicate
across long distances. The noise associated with seismic surveys
can affect the ability of these animals to detect natural
underwater sounds, thereby disrupting these critical activities.
Numerous scientific studies have solidified what Eskimo
subsistence hunters have known for years: that whales avoid
expansive areas where seismic surveys are being conducted. One
recent study showed that fall–migrating bowhead whales in the
Beaufort Sea were displaced from an area within 12 miles of the
seismic source and began to show avoidance behavior up to 21
miles away. Researchers have also observed signs of physical
stress such as startle responses in humpback whales while
seismic surveys were being conducted many miles away.
INLETKEEPER’S SOLUTIONS
For more information on the
state’s leasing program in Cook Inlet, contact
Bob Shavelson or
Lois Epstein.
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