Oklahoma just had another 5.0 earthquake. People are most anxious to blame these increasing quakes on fracting and water injection. But I propose it is not at all. Even in geologically wild California, the injection of water into deep wells only causes small quakes below the 3.5 threshold. Oklahoma, Kansas and Nebraska have many buried deep faults and even slip-lock type faults like we see in California.
Note the depths here! In Northern California there are increasing numbers of shallow (relatively speaking!) quakes but the ones in the middle of the country are at ‘normal’ depths. The recent ones this week in Wyoming, on the other hand, are right at the surface. This is the sleeping dragon of monstrous size snoozing in Yellowstone.
Jumping to conclusions, a Scientist finds possible cause of 5.6 Oklahoma earthquake in November 2011 which is, interestingly for psychological reasons, caused by humans according to him:
For months we’ve been looking into a large earthquake that shook the state this past November.
Scientists shared new information with us about its possible cause.
While thousands of earthquakes were being tracked in Lincoln County last year, thousands of gallons of wastewater were being injected into wells nearby.
Once water is used to help get oil and gas out of a rock, that water is later disposed of and goes into an injection well a mile or more deep. In Lincoln County alone there are almost 200 injection wells, that’s where a 5.6 quake shook the state in November.
“There are three injection wells that are located within five kilometers (3.1 miles) of the main shock,” said Dr. Steve Horton for the Center for Earthquake Research and Information.
Here is this month’s map of recent earthquakes: Leonard Geophysical Observatory – Recent Earthquakes
They are scattered all over the state but mostly dead center near Oklahoma City and southwards. Here is a list of recent quakes:
I see the same thing over and over again: they are almost all at five km depth. A deep human injection well can go down to 9,000 feet but 5 km is over 16,000 feet. This injection process could cause earthquakes but not the series of 4.0+ quakes we have been seeing lately. Are Fracking Wastewater Wells Causing Ohio’s Earthquakes? – Popular Mechanics asks about this happening in Ohio. The change in water movements in the earth could trigger these quakes but something more may be going on here that is much more disturbing.
That is, we could be heading towards a near-simultaneous San Andreas/New Madrid Fault movement event. The entire continent is pressing hard against the Pacific Plate and the tied-up section that must slip eventually is causing stresses to accumulate far from the site of the locked-up movement.
I decided to look harder at the geology of Oklahoma and yes, that state most certainly does have more than one fault line as well as a fair amount of complex geological formations.
The southern half of the middle of the state has the most folds. But the quakes are near an interesting geological formation in the center of the state which we can see a hint of in the map below:
So, there is this thing called the Nemaha Shale Formation intersecting with the Anadarko basin and the Arbuckle Uplift and the Cherokee Platform. Here is a paper about the Nemaha Shale system:
So, these are NOT ‘normal faults’ but complex faults. A listric fault is curved like a bowl. This resembles the fractured mess that is the Rocky Mountains only this is buried under flatlands. The ‘left-lateral strike-slip movement’ business is what is going on in California’s San Andreas. There could be considerable stress building in these hidden fault systems and yes, geological activity at one end of the continent can certainly impact the center section.
We still little understand the New Madrid Fault business! And the mining and extraction businesses do affect geology but I believe that natural forces are even more at work here since the proliferation of quakes has increased far away from the West Coast which is very definitely itching to have some serious action.
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