Only, it costs about $10 million a pop.

A thorough seismic survey to assess tracts of rock below where oil and gas drilling fluid is disposed of could help detect quake prone areas.

But that would be far more costly than the traditional method of drilling a bore hole, which takes a limited sample of a rock formation but gives no hint of faults lines or plates.

The more expensive method will be a hard sell as long as irrefutable proof of the link between fracking and earthquakes remains elusive.

"If we knew what was in the earth we could perfectly mitigate the risk of earthquakes," said Austin Holland, seismologist at the Oklahoma Geological Survey. "That is something that we don't have enough science to establish yet."

A 4.0 New Year's Eve quake in Ohio prompted officials to shut down five wells used to dispose of fluid used in the hydraulic fracturing process. That comes less than a year after Arkansas declared a moratorium due to a surge in earthquakes as companies developed the Fayetteville Shale reserve.

Experts say the quakes do not necessarily appear to be caused during the process of fracking, a controversial extraction technique that involves injecting chemical-laced water and sand into shale rock to release oil and gas.

Instead, it's the need to dispose of millions of gallons of contaminated fluid extracted from each drilling site, either to be recycled or trucked to a separate location to be pumped deep underground.

The pressure caused by water pushed far below the surface for a long period has been linked to an increase in seismic activity, as water enters fissures and lubricates fault lines which can cause earthquakes in places otherwise free of them.

"It basically greases the wheels of the earthquake process that is there naturally and causes the earthquakes to occur at lower stress levels than they might normally have needed to occur," said Larry Brown who chairs the Department of Earth and Atmospheric Sciences at Cornell University in Ithaca, New York.

Precautions can be taken to mitigate risks of earthquakes near disposal wells, such as lowering injection pressure and avoiding areas with a history of seismic activity, though none of these guarantee total safety.

QUESTIONED LINK

On paper, the link between fracking and quakes is compelling. As the oil and gas industry embarked on a massive expansion of hydraulic fracturing across Arkansas, Pennsylvania and elsewhere, the number of earthquakes in areas where wastewater was injected back underground surged tenfold.

Data from Columbia University's Lamont-Doherty Earth Observatory, which had seismographs set up in Youngstown on Saturday, concluded that the earthquake occurred at the same depth as the well, about 2 miles below the surface.

"There is a relationship between when they started to inject into the well and the earthquakes started near the bottom of the well so it is unlikely to be coincidental," said John Armbruster at Lamont-Doherty.

But some researchers say the link has not been proven.

In Oklahoma, which saw a tenfold increase in earthquakes since 2009 to over 1,000, officials at the Oklahoma Geological Survey (OKGS) say more proof of a link to fracking is needed.

"The strong correlation in time and space as well as a reasonable fit to a physical model suggest that there is a possibility these earthquakes were induced by hydraulic fracturing," according to a OKGS report released in August. "However, the uncertainties in the data make it impossible to say with a high degree of certainty."

(Additional reporting by Kim Palmer and Julie Steenhuysen; Editing by David Gregorio)

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