The Mississippi around New Madrid fault zone going dry?

[Al Agnew]

The San Andreas Fault and associated ones in California are far more likely to produce the next huge American earthquake than the New Madrid Fault, even if the guy I read was wrong and the New Madrid one isn't going completely dormant.

The book is "Disaster Deferred--How new science is changing our view of earthquake hazards in the Midwest"  by Seth Stein.  Basically, he and other seismologists have been GPS measuring movement of the earth in a wide area surrounding the faults.  A typical earthquake is along a fault where there is movement (in opposite directions) of the tectonic plates on either side of the fault.  This movement can be measured.  It shows up in the parts of the plate that are farther from the fault, but along the fault, the plate boundaries are stuck.  So the rock bends (yep, rock does bend) as the movement further away continues while the part of the plate next to the fault stays stationary.  When the stress that is building up reaches a breaking point, the fault gives way all at once, and so the edges of the plate along the fault "instantly" catch of with the movement elsewhere.  So what Stein says is that measurements all around the New Madrid complex of faults shows NO movement either close by or farther away.  No movement farther away means no stress building up around the faults, and no possibility of a major earthquake.  (And current GPS technology means they can measure earth movements as little a 1/25th of an inch.)

Yes, Wrench, faults can go completely inactive.  There are a ton of faults throughout the Ozarks that haven't been active in millions of years, and won't be active for millions more, at least.  There is a major fault a quarter mile from my house, the Ste. Genevieve Fault, the two sides of which moved as much as a mile in the distant past (on a vertical plane--the rock underlying my house is 4000 feet beneath the surface on the other side of the fault).  It is completely inactive as far as anybody knows, now.

[Quillback]

Sounds like an interesting book.

[Kelroy]

https://www.snopes.com/mississippi-river-going-dry/

The John Schumacher interviewed is the Data Chief in charge of the Ground Water and Water Quality sections at the Missouri Water Science Center (USGS), the folks who are responsible for the monthly discharge measurements and sediment/water quality sampling at Grafton, St Louis, Chester, Thebes, and New Madrid. If anyone cares to see for themselves, they can pull up the web pages for Thebes and Memphis and see how the discharge over the last couple months compares to the historical daily mean. There is not much data from the New Madrid gage, as it was only recently renewed for study and an accurate stage/Q rating is still in development.

As Al pointed out in an earlier post, channel morphology plays a key role in determining the stage/discharge relationship in any river. Flood events can radically affect the channel on both the rising limb (scour) and the falling limb (deposition) of the hydrograph. In the case of the Missouri and Mississippi Rivers, the bottom is almost entirely sand which, above velocities of a couple feet per second, is constantly shifting. This 'moving bed' results in the building, migration, and collapse of sand dunes along the river bed. It is the action of these dunes (most notably when they collapse) that causes the occasional 'boils' or 'swells' one sees on otherwise smooth water. It is this dramatic and constant changing of the bottom which necessitates the monthly measurements on our larger rivers, in order to keep their gage height/discharge rating formulas as accurate as possible. ~K

 

[awhuber]

https://www.shakeout.org/centralus/

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