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Midwest Earthquake Hazard Downplayed
swellconvivialguy writes "Next year marks the bicentennial of the 1811-12 New Madrid earthquakes, with earthquake drills and disaster tourism events planned across the Midwest, including the Great Central US ShakeOut. But despite the fact that Earthquake Hazard Maps equate the New Madrid seismic zone with California, geologist Seth Stein says new science (especially GPS data) tells us that the hazard has been significantly overestimated, and that we should not spend billions on earthquake preparations in the Midwest."
Was going to give eldavojohn a tl;dr flame because he sounded a bit like one of those bad slashdot commenters dissing scientists' real work in favor of intuition, but I recognize his nick and that's not his style. On rereading, Eldavojohn prolly is asking like he did because he's curious and the issues seem counterintuitive, not because he thought he was being insightful (stupid mod system needs a '+1 good question')
Earthquakes and plate tectonics don't map ideally to simple, intuitive physics. Then again, nothing does.
IANAG, but the earth's surface as a giant rubbery sheet analogy works a bit *IF* one remembers that every atom in that giant sheet of rubber has net-force vectors pulling them. Lower layers that are well-adhered causing drag, other areas that move more easily, gravity, surge/subsidence due to deep-crust activity, hydraulic forces (literally, as in aquifers causing pressure/flow), shear forces and edges where contradictory motion causes drag. And compression, which is stored energy. Some geological structures are really boring (stable) and all of these forces are minor. I'm guessing that'd be the US midwest. Others could have an order or two of magnitude more action.
We get a glimpse of these dynamics (especially compressive forces, movement and accumulated shear forces) by tracking positions carefully. I ran into this monitoring huge dams: if monitoring points' relative positions across both a dam and the canyon walls adjacent remain fairly uniform, life's good. If anything (or the 2nd-order function: rate of movement) changes dramatically, it's cause for immediate attention/study/alarm: water leakage, subsidence, fracturing... any of them could lead to collapse. That's probably a gross oversimplification of what TFA was reviewing, but if all the deltas (movement) in an area are trivial and there's no history or evidence of faultlines, that's a safe area. If movement is substantial, nonuniform, sporadic... that's not. Now, why the hell am I handwaving my way thru this crap? Where's a geophysicist when we need one?!