Saturday, October 5, 2013

Latest thoughts on New Madrid earthquake zone

During the US gov't scientist furlough, I reign supreme!  Muhaha!  Canadian scientists are all muzzled, and university scientists are all busy publishing in shady journals.  I could publish in a vanity 'publish or perish' journal, too, but I would never want to be in a journal that would have me.  :)

So I noticed that everybody wants to ask about the New Madrid fault zone.  I have finally crystallized my thoughts on this, which means I cast a hypothesis and wait for further data to confirm or destroy it.  This is what a 'purist' does (hey Mr. Climate Person?).

With the new experience in Arkansas, I am now convinced that the New Madrid events were a one shot deal.  All of the Precambrian megathrusts are under high stress, and it just takes a little water.  Especially in Arkansas, it has been shown that a steady injection of water can grow a baby New Madrid.  You could easily duplicate this with finite difference computer modelling, or a testing machine.

So, at one time in the past thousand years or so, the Mississippi changed course, and placed a lot of water on top of a vital drain.  This initiated the sequence, and each shift in the earth allowed more water to penetrate.  The earthquake zone grew until it reached its penultimate, which was the series of M7.7 earthquakes that penetrated the entire crust and reached the edges of the fracture zone.  Stability here means that the water flow has ceased, and equilibrium has been reached.

Does this mean that everybody in the region can build soft-story condos on swamps?  No, the general seismic hazard for the region is probably the same as any other place in the East, including Toronto.  New Madrid was a huge disturbance to the local stresses.  The figure shows my estimate of the stress-relieved zone.  We must expect M6 or 7 activity at the boundaries, provided there is a deep drain for water.  These will be excellent places for waste water injection!  :)

So, I relegate the hazard and risk to the same as anywhere else.  As I have mentioned before, engineering is wrong in supporting floppy buildings on soft soil.  We won't see much with an M6, such as Virginia, but an M7 is a different story.  In the meantime, everybody should be happy!

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