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A primer on seismic testing

Posted April 9, 2015, on www.islandfreepress.org.  Used by permission.

The Bureau of Ocean Energy Management will sponsor a public meeting on seismic offshore seismic testing at Ramada Plaza Nags Head Oceanfront, 1701 S. Virginia Dare Trail, Kill Devil Hills. One meeting starts at 3 p.m. and the other at 5:30 p.m. Each lasts about 90 minutes.

04.09.2015-APrimerOnSeismicTesting

By KIP TABB Coastal Review Online

One of the flash points in the debate over developing possible offshore oil and gas centers on seismic surveying, an effective but controversial method used in the search for energy deposits.

Three public meetings have been scheduled this month about using “air guns” off the N.C. coast. The first was in Wilmington, the second was April 9 in Morehead City, and the last one is on Monday, April 27, in Kill Devil Hills.

Here’s a primer to help you understand what all the noise is about.

What is seismic surveying?

It’s an exploration method that uses pulses of sound that are projected into the earth’s crust. As the sound rebounds, the pulses are analyzed and from that data images of the layers of sediment, rock and hydrocarbons up to 10,000 feet below the surface can be created.

The technology is used to search for hydrocarbons on land and in marine environments. It is also used by doctors when giving ultrasound examinations to pregnant women.

Is this a new technique?

Not really. Land-based seismic surveying has been used since the 1920s, although the early methods used to create the pulses of sound would be considered downright primitive by today’s standards—the survey team would set off dynamite at the bottom of a shaft they had drilled.

Marine seismic surveying was developed in the 1960s. Technology had advanced to the point that a method of sending a bubble of sound to the bottom of the ocean had been developed and the returning sound waves could be interpreted by the improving computer technology.

How does marine seismic surveying work?

An array of “air guns” are towed behind a ship, and at timed intervals, a pulse of sound is directed to the seabed. The term air gun may not be quite correct, though, according to Stanley Labak, an expert in marine acoustics with the Bureau of Ocean Energy Management, or BOEM. That’s the federal agency that regulates offshore energy exploration and production

“Air gun is the terminology in the industry since its inception . . . in the early ‘60s. But it’s not really a gun. It’s a chamber that has pressurized air in it and at a set time they release that air and it forms a bubble and it creates sound,” he said.

Read the rest of the story here.

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