Seismic Airgun Blasting
Anika Kim
December 17, 2018
Submitted as coursework for PH240, Stanford University, Fall 2018
Background
As the United States looks to enlarge
offshore exploration of oil and natural gas
in federal waters, the Trump
administration recently approved the use
of seismic gun blasting to find oil and
natural gas deposits buried deep in the
ocean floor in the coast of Alaska. [1] It is
believed that the largest untapped onshore
supply of oil lies underneath the Arctic
National Wildlife Refuge along the coast
of Beaufort Sea and while years of
protection and opposition to drilling have
kept the area largely off- limits to oil Fig. 1: Seismic Airgun Blasting
(Source: Wikimedia Commons)
companies, it is all about to change. [1] As
seismic gun blasting is only the beginning
of the governmental efforts towards offshore drilling, it raises several environment
concerns, not least concerning marine life and climate change.
Seismic Source
Seismic instruments refer to technology that releases energy into the earthin this case,
into the oceanin the form of controlled seismic waves. [2] Marine seismic sources thus
release seismic waves into the ocean to explore a given marine environment via
reflection and refraction surveys. Once these seismic waves and reflected and
refracted, they are recorded by seismic sensors, such as geophones or hydrophone.
[2,3] These data are then gathered and analyzed for information about locations of
potential petroleum reservoirs and mineral deposits. The most commonly used marine
seismic source is the seismic air gun, which is fired from the bottom of a ship usually,
as shown in Fig. 1. Seismic air guns are often made up of two chambers and a shuttle,
which looks very similar to a piston. Highly pressurized air moves from the bottom
chamber to the top chamber through the shuttle and eventually, forces the top chamber
upwards, resulting in the firing of highly pressurized air into the ocean. [4]
Environmental Implications
The use of seismic air guns has significant environmental implications. Seismic air
guns are fired every ten seconds for 24 hours every day and it could last from
anywhere to days to several weeks in a row. [5] According to a report by the Bureau
of Ocean and Energy Management, seismic airgun testing could injure up to 138,000
whales and dolphins. [5] Five species with the highest amount of impact are
bottlenose dolphins (up to 11,748 individuals/year), short-beaked common dolphin
(up to 6,147 individuals/year), Atlantic spotted dolphin (up to 5,848 individuals/year),
short-finned pilot whale (up to 4,631 individuals/year), and striped dolphin (up to
3,993 individuals/year). [5] This is due to the fact that seismic blasts loud sound,
which travels very long distances. Before reaching the sound reflection surfaces, the
seismic waves will first reach marine animals, which will result in severe injuries and
even death in some cases. For marine animals like whales and dolphins who primarily
use sound for communication, feeding, and mating, seismic airgun blasts have the
potential to disrupt all three processes. Furthermore, these sounds could easily scare
away fish from their normal habitat and result in temporary and permanent hearing
loss in several animals, severely disrupting marine ecosystem. They can also directly
kill fish eggs and larvae. As the United States looks to use seismic airgun blasting to
look for oil and natural gas reservoirs near Alaska coasts, they must also think about
how to prevent these severe damages to the marine ecosystem from happening, which
is only the beginning of the larger health consequences that will be sure to come once
oil drilling begins.
© Anika Kim. The author warrants that the work is the author's own and that Stanford
University provided no input other than typesetting and referencing guidelines. The
author grants permission to copy, distribute and display this work in unaltered form,
with attribution to the author, for noncommercial purposes only. All other rights,
including commercial rights, are reserved to the author.
References
[1] H. Fountain and S. Eder, "In the Blink of an Eye, a Hunt for Oil Threatens Pristine
Alaska," New York Times, 3 Dec 18.
[2] R. E. Sheriff, Encyclopedic Dictionary of Exploration Geophysics, 3rd
Ed. (Society of Exploration, 1991).
[3] E. Onajite, Seismic Data Analysis Techniques in Hydrocarbon
Exploration (Elsevier, 2013).
[4] M.-H. Zhao et al., "Large Volume Air-Gun Sources and Its Seismic Waveform
Characters," Chinese J. Geophys. 51, 400 (2008).
[5] "Atlantic OCS Proposed Geological and Geophysical Activities," U.S. Bureau of
Ocean Energy Management, BOEM 2014-001, Vol. I and Vol. II, February 2014.
