Scientists still not certain about cause of 5.7-magnitude quake in Oklahoma
BY WAYNE GREENE World Senior Writer
Friday, December 07, 2012
12/07/12 at 7:33 AM
Whether a 5.7-magnitude earthquake that shook Oklahoma in 2011 - the biggest in contemporary state history - was man-made is still an open question, state geology experts say, and regulators say so is the issue of whether they should do anything about it.
The Nov. 5, 2011, earthquake near Prague - which was felt widely across the state - was "likely triggered" by fluid injection in the area, according to a paper presented Wednesday by University of Oklahoma seismologist Katie Keranen at the fall meeting of the American Geophysical Union in San Francisco.
But Oklahoma Geological Survey officials say there's a significant and important distance between likely and certainly.
In fact, there may never be enough evidence to make a definitive finding about what caused the Prague earthquake, said Austin Holland, research seismologist for the Oklahoma Geological Survey, in a telephone interview from the San Francisco conference Thursday.
"If you assume that the Prague earthquake is triggered, you don't have enough data to show it's a natural earthquake. If you assume that the earthquake is natural, you don't have enough data that shows it is clearly induced," Holland said. "Our position is that until you can prove that it's not a natural earthquake, you should assume it's a natural earthquake."
Keranen's research uses aftershocks to document the fault patterns responsible for the earthquake and uses the timing and proximity of the earthquakes with injection wells and subsurface structures, according to an abstract of her presentation on the geophysical union's website.
But Holland pointed out that's less than clear cause-and-effect evidence.
Holland took 92 earthquakes that have been potentially linked to Oklahoma fracking activities between 2010 and mid-2012 and determined that the number was almost equal what would be have happened as a result of mere chance.
His point: While human activity has been proven to sometimes cause earthquakes, without clear evidence of linkage, you can't say that a particular event was man-made.
"A healthy skepticism only makes good science better," he said. "You really have to look at this on a case-by-case level."
A spokesman for the Oklahoma Corporation Commission said the agency hasn't come to any conclusions about the dangers of man-made earthquakes - or "induced seismicity" in geology jargon.
"We have a completely open mind on this topic," commission spokesman Matt Skinner said.
The commission has turned to the state geological survey to investigate the issue, but until it comes up with conclusions, the issue is unresolved, he said.
"The research continues, and the commissioners have an open mind," he said. "It's an open question."
Skinner pointed out that the Prague earthquake clearly wasn't due to fracking because there was no fracking going on in the area.
A deep injection well in the area has been the target of some speculation, but that well isn't involved in fracking and isn't disposing of fracking waste, he said.
Holland said falsely identifying a natural earthquake as something man-made would have reverberations beyond the scientific community. An induced earthquake would not be included in U.S. Geological Survey's hazard calculations, which are used to create and update building codes and establish construction requirements.
While he hopes to someday have enough information to determine the cause of the 2011 earthquake, Holland said it may never be available.
"The problem is the kind of data we need is really needed ahead of time, and I really don't think it exists out there," he said.
Could the Prague earthquake have been man-made? Holland says his best answer at this point is: maybe.
"It's clearly possible, but if I had to given it a probability at this point it's like 50 percent. I'm right there on the fence," he said. "There just isn't the information that says it has to be."
Original Print Headline: Certainty of quake's cause still elusive
Wayne Greene 918-581-8308
wayne.greene@tulsaworld.com
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Austin Holland: The seismologist says the 5.7-magnitude quake in 2011 might be man-made, but there's not enough data to know for sure
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