One cannot totally rule out an earthquake triggered by oil and gas extraction in West Virginia, but the likelihood of this, based on historical evidence, is remote to say the least, lawmakers were told Tuesday.

Such was the conclusion given to lawmakers by Michael Hohn, director of the West Virginia Geological and Economic Survey.

“Hydraulic fracturing does not pose a high risk, based on 35,000 shale wells today,” Hohn told Judiciary Subcommittee A.

There have been two, possibly three, such tremors linked to hydraulic fracturing, one of them in Oklahoma measured at 2.8 on the Richter scale.

Hohn said it is “difficult” to draw a parallel between gas extraction and seismic activity.

Last year in England, a quake with a magnitude of 2.3 led the extraction company to take responsibility for fracturing right inside a fault, he said.

“So, the potential is there,” Hohn said.

“But the number of incidents to date is very small.

Attempting to discern the prospects of an earthquake prompted by a deep injection is difficult because most of the time the depth of underground faults isn’t known, the geologist said.

On average, West Virginia is known to experience one or two earthquakes every year.

“But they’re very small, hardly noticeable in most places,” Hohn said.

Effects of quakes are classified as hazard, the physical traits such as the ground trembling and noise, and by risk, the structural damage, injuries and deaths.

“You really cannot predict the future,” Hohn told the legislators.

“There is no reliable prediction of earthquakes anywhere in the world, other than on a statistical basis.”

The magnitude of an earthquake is the amount of energy discharged, and this hinges on the total area of the fault, Hohn explained.

Generally, the quakes recorded in West Virginia have ranged between 3 and 3.5 on the Richter scale.

“You’ll feel them,” Hohn said, noting a favorite dish handed down by a grandmother could topple from a hutch and smash on the floor, while automobiles can move.

A swarm of quakes occurred two years ago in Braxton County, but most of them occurred at a time when a seismometer was being upgraded, Hohn said.

Most were of the magnitude of less than 3, he noted.

“People did feel them,” Hohn told the panel.

“Persons described them as sounding like a car hitting your house if you were inside.”

From an industrial standpoint, however, Hohn suggested there seems to be little concern that extraction and injection in the removal of gas will result in earthquakes.

“A very small fraction of the hundreds of thousands of wells for injection and extraction have induced seismic levels noticeable to the public,” he said.

Those that have occurred are spawned by the changes in pressure created by the injection or puling out of fluids.

“In conventional oil and gas recovery, there have been rare cases of oil and gas being withdrawn causing earthquakes,” he said.

Various criteria are employed to ascertain if an injection could lead to seismic activity, he said.

Have large quakes occurred before? What is the proximity to the drilling site? How about the rate of activity near the operation? Were injection practices and the pressures employed sufficient to prompt earthquakes?

“Most of this list leaves West Virginia out in the sense that it’s really a list for California and Alaska, the Middle East, Japan,” Hohn said.

“We are not in an area of high Teutonic activity. Earthquakes are relatively rare. They tend to be spotty. Again, only a handful per year almost, unless you get one of those swarms.”

— E-mail: mannix@register-herald.com