Sunday, January 3, 2016

Oklahoma earthquakes by the numbers

Every day another 5,000 join my Earthquakes collection (not quite).  They are from all over the world and barely speak English.  But they are totally puzzled by Oklahoma, and once in a while I do a summary.



Here's where it now stands, on the verge of another big earthquake today or tomorrow.  You can find this all by reading endless amounts of my previous posts.  -- Ha!

It all starts with our North American plate under tremendous NE horizontal stress.  It is slowly being squeezed by plate margins, but most likely the stress comes from sinking into a cold zone (press your thumb on a beachball).  Nobody disputes this.

Now, unlike California, nothing ever happens here, so the stress is at the limit state, ie. just a little bit more and you have an earthquake.  The last exciting thing was the glacial advance.  All this stress is carried in the Precambrian basement, right down to the Moho (bottom of the crust).  We Canadians have imaged it, but the Americans are afraid of it.  They only know Paleozoic geology.  They have every right to fear it (just like the Bruce Black Hole), but it is a sleeping tiger.

Every once in a while, somebody tweaks the tail of the tiger.  This is done by sending surface water (from rain) down deep.  This has been done naturally over the millenia, mainly by the ice sheets and their leftovers.  One major leftover, was the current course of the Mississippi River.

That happened to lie right over a significant PreC structure, which I have dubbed a megathrust.  We can see them clearly on Canadian imaging, but the busgus puts all their money into Callie.  Over the thousands of years, water seeped into the deep crust and started a growth process of stress relief, ending in the monster earthquakes of 1811.  These were so huge that if they came again, they would destroy the entire Midwest.  Now, it's funny that they are all poo-poo about it rising again, and they used that to get money, but this is a dead parrot.

Now we get to OK and the raising of the next New Madrid earthquake sequence.  I first got into this when they tried it in Ohio and Arkansas, but quickly stopped when they hit M4's.  OK has got well beyond that.

It's cute that they've been injecting deep salt water for a long time.  But they never had the current volumes.  If you just inject into the Cambrian sandstones then nothing happens, but it only takes dribbles.  For real volume, you have to directly inject into the PreC open fractures.  Infinite volume!  Infinite rate.

It starts with one hole into the megathrust, perhaps through the open limestone above.  Let's say this was the Prague structure, line D.  It very quickly escalated into an M5.6 and they shut it down -- Oops!

Up to the next structure, line A.  How do they find these?  They know what's down there.  Otherwise you drill into tight rock, and not a speck of injection.

Happy injecting with deep water, saturated in silica.  It's not aggressive to the quartz holding the faults together.  It's all open so there is no pressure.  La, la la!  Money, money.  But fracking has started in volume and we can inject surface water.  First earthquake.  It opens the rock more.  Money, money.

Everybody and their dog jump into this money pond.  Fault A is slipping in an oblique manner.  It can't really slip too much without putting pressure on the end points, so Fault C starts compression.  Every thrust fault here allows A to slip more.  This is exactly the mechanism at New Madrid with a central thrust, and two shear wings.

It goes on, and time to start Line B.  It doesn't have a thrust fault yet, but is crumpling with longitudinal cracks (normal faults) at the ends.

Line B has a big paroxysm in December, and puts strain on Line A which is now in paroxysm.  Thrust fault C can put some good motion on OK City.

There you have it.


2 comments:

Barbara Bowman-Fuller said...

Harold you are Seriously creating a very frightful scenario for not only Oklahoma, but also a lot of surrounding states. The Press is actually sounding more "serious" regarding the quakes, no longer the "Oh nothing to worry about" statements, now we are seeing actual brick wall,fireplace crumbling results. It's going to get worse isn't it? Thanks for all of your hard work!

Harold Asmis said...

It's always been serious.