Sunday, September 6, 2009

Seismic survey in Lancaster County

I've been away for a bit: archaeomagnetic sampling and magnetic surveying at the Etruscan site of Poggio Colla in Italy; improving my field geophysics with folks at the Bayerisches Landesamt für Denkmalpflege in Munich; presenting a talk on magnetic properties of legacy sediments at the IAGA symposium in Sopron, Hungary; and along the way also enjoying the Venice Biennale and Budapest.

Anyway, what is shaking around here these days is seismic, but not an earthquake, It's a big truck. Lancaster County is getting "x-rayed" via vibroseis. Funding comes from Pennsylvania's carbon sequestration program.

Here is the full newspaper story, by PJ Reilly, from the Lancaster Intelligencer Journal, Jun 17, 2009:
A statewide project aimed at reducing Pennsylvania's carbon dioxide emissions could provide a first look at what's below the surface of Lancaster County.

"No one's ever drilled it deep," said Jay Parrish, director of the Bureau of Topographic and Geologic Survey for the state Department of Conservation and Natural Resources. "No one's ever done seismic work. All we know is what's at the surface.

"Everybody has seen the surface of Lancaster County for 250 years. Go down 3,000 feet and it's a complete mystery."

If his funding holds up, Parrish hopes to deploy a team to Lancaster County in August to literally pound the ground, north to south and from end to end, and take seismic readings to develop a picture of what lies deep beneath the surface.

"It's like a new world no one has ever looked at," he said. "We have no idea what's here."

DCNR is studying Pennsylvania's geology as part of the requirements of House Bill 2200, which was signed into law in October by Gov. Ed Rendell.

The bill orders DCNR to evaluate the state's potential for "geologic carbon sequestration."

According to the agency's Web site, that's a process in which carbon dioxide emissions are captured at coal-fired industrial plants before they are released into the atmosphere for injection and storage deep underground.

Pennsylvania ranks third among all 50 states for its total emissions of carbon dioxide, which is a greenhouse gas linked to global warming.

One percent of all the carbon dioxide emitted into the atmosphere in the world comes from Pennsylvania, Parrish said.

"As part of a broader portfolio of technologies, geologic sequestration appears to be capable of playing an important role in stabilizing carbon dioxide concentrations in the atmosphere," DCNR's Web site states.

Preliminary studies and general knowledge of Pennsylvania's geology suggest it is well suited for geologic carbon sequestration, which requires reservoirs a half-mile or more underground that are sealed by impermeable layers of rock, the Web site states.

Four primary reservoir areas DCNR expects to find are deep saline formations, depleted and producing oil and gas fields, coal beds that can't be mined and organic-rich shales.

Parrish, who was director of Lancaster County Geographic Information Systems department from 1997 to 2001, said his DCNR bureau has been assigned the task of studying the entire state to find such areas and others that might be suitable for storing carbon dioxide.

Scientists already know what lies beneath many areas of Pennsylvania, where coal mining and gas- and oil-well drilling have been going on for years.

But the extreme southeast corner of the state, including Lancaster County, is unexplored territory.

"Theoretically, there's no oil here, and that's why nobody has ever looked," Parrish said.

Discovering what lies beneath the county is important, according to Parrish, not only to see if the potential for carbon sequestration exists here, but also to simply have the subsurface data available.

"What does it mean to the average person?" he said. "It means there's a better understanding of the rocks under them, and that leads to every aspect of life, because you have radon flows, you have earthquakes, you have sinkholes.

"You just don't know what potential is there, and you also don't know, in the future, what may be useful information to have."

On Dec. 27, an earthquake measuring 3.4 on the Richter scale rattled Lancaster County. The epicenter was just west of Manheim Borough.

That's one of the areas Parrish wants to explore. He said scientists suspect there's a fault there, based on formations found in some local quarries.

"What we're looking at are little tiny thrusts at the top, so we have a good indication there's a fault there," he said. "But we don't know, maybe there's a huge faulted thrust underneath."

DCNR has budgeted about $3 million to collect seismic data from 41 of Pennsylvania's 67 counties, including Lancaster.

Parrish said the "project is in a constant state of flux" and "my priorities change from week to week," which could mean there won't be enough money to study Lancaster County.

For now, however, Parrish said the plan is for a seismic team to descend on the county in August.

He said it would take about three weeks to get readings along a north-south line through the heart of the county.

Since most of Pennsylvania's geologic formations run east to west, a north-south survey near the center of Lancaster County will give scientists a "pretty good idea" of what the whole county looks like beneath the surface, Parrish said.

To collect data, a large truck carrying a heavy weight would crawl along back roads at a rate of about 3 miles per day. Highways generate too much noise, which would interfere with the seismic readings, Parrish said.

Periodically along the route, the weight would be pounded on the ground and a series of small seismometers attached to a cable, which would be extended for three miles on both sides of the truck, would track the vibrations.

The data would be plugged into a computer "to give us a nice picture of the underground" up to three miles deep, Parrish said.

Ideally, Parrish would like to take readings on a perfectly straight line down the center of the county.

"Obviously, that's not possible with the roads we have around here," he said.

The line of readings likely will zig-zag along public roads.

Once he knows for certain there's enough money to study Lancaster County, Parrish plans to map out a work route and then contact officials in municipalities along that route to let them know what's happening.

"It's going to be a pretty big production that's going to attract a lot of attention," he said. "And we want people to know ahead of time what's going on."

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