Seismic Wave Mapping Rolls On
Pittsburgh Tribune-Review
18 September 2010
By Stacey Federoff
A convoy of trucks rumbled along Route 31 near Mt. Pleasant this week
following a trail of black cable.
The trucks are a part of a monthlong speculative survey using seismic
waves to map underground layers of rock, said Annette Evans, president
and owner of Michigan-based Evans Geophysical Co.
Evans said the company has already acquired seismic data from more than
2,000 miles throughout the Appalachian Basin, including areas of
Pennsylvania, New York, West Virginia and Kentucky, with 500 miles left
to acquire.
The data is used to compile maps that help oil and gas companies
determine where to drill for gas within the Marcellus shale formation,
she said.
Evans Geophysical is a broker who contracted Dawson Geophysical Co.,
based in Dallas, to collect the data in southwestern Pennsylvania,
which her company will use to form a two-dimensional underground map.
Three large trucks generated the seismic waves, pressing plates to the
ground in unison, said Matt Leist, regional manager for Dawson
Geophysical.
The waves, which reach about the width of the roadway and between 5,000
and 8,000 feet deep, are then sent to devices called geophones. The
geophones then receive the waves and send them as data to a recording
truck, where it is stored on a tape or DVD, Leist said.
"Every time (the trucks) shake, the sound waves they put out come back
to the geophones," he said. "It's very precise, but it's two
dimensional straight down and straight up."
The geophones are connected every 700 feet together with cable, which
can stretch as far as 12 miles at a time before it is moved by the
surveyors, Evans said.
On Wednesday, the cable stretched most of the distance between West
Newton and Mt. Pleasant along Route 31, taped down in some places to
cross intersections, and down Main Street in Mt. Pleasant.
Evans said the data is then used by geophysicists to create a map of
their findings.
"We end up ultimately owning the data, but we license it out to other
oil and gas companies," she said.
Drilling companies in search of gas within the mile-deep Marcellus
shale formation in the region can use the maps to help determine its
location, Leist said.
"It may show the structures where gas or oil may exist, but it may not
be there," he said. "(A map) cuts down the risk for drilling, but it
certainly doesn't eliminate it."
The surveyors will travel about 5 to 6 miles per day, depending on the
weather, and will be traveling in the area for at least four more days,
Leist said. They plan to map Route 31 to the Somerset County border.
Seismic surveying has been used for more than 50 years and has no
effects on the environment, he said.
A spokeswoman with the state Department of Environmental Protection
said no permits are required through the department for seismic mapping
because it is not regulated by the state.
PennDOT spokesman Jay Ofsanik said permits are granted for the trucks
to travel on the state highways, like Route 31, using the seismograph
method to survey like Dawson Geophysical.
In April, residents in Damascus Township, near the Pennsylvania-New
York border in the northeastern part of the state, were concerned after
similar surveying took place there.
The Wayne Independent reported that citizens did not want the company
on their private property, but most of the surveying was being done on
roads' right-of-ways.
Ofsanik said the right-of-way granted near the highway varies, but if
residents are concerned they can contact PennDOT.
"There's no general rule for what the right-of-way is," he said. "If
there's a question there, they can check with us."
Leist said the surveying has little to no effect on nearby property.
"There's absolutely no harm to the environment in any way," Leist said.
"We finish our survey, we pick up everything and we leave."
Stacey Federoff can be reached at sfederoff@tribweb.com or
724-836-6660.