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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."
When we look at faults around the world, we see them storing up that energy. So when we first put markers in the ground and measured the position of the Midwestern fault lines we were surprised that we didn’t see any motion at New Madrid. We concluded that there’s no sign that a big earthquake is on the way.
I'm not a geologist so I'm very confused, if something is 'storing up energy' how does moving around equate to that? I mean, if the moving of the ground in violent ways is the releasing of that 'stored energy' then how is small movements indications that it's storing up energy? I would assume that the worse earthquake areas are those when there's a lot of movement going on deep underground but nothing on the surface releasing that energy until a very devastating movement.
So from the Wikipedia article:
The lack of apparent land movement along the New Madrid fault system has long puzzled scientists. In 2009 two studies based on eight years of GPS measurements indicated that the faults were moving at no more than 0.2 millimetres (0.0079 in) a year. This contrasts to the rate of slippage on the San Andreas Fault which averages up to 37 millimetres (1.5 in) a year across California.
Can somebody who knows a lot about this stuff explain to me why we are so sure that a lack of movement in GPS measurements indicate no potential earthquake? My intuition would guess that no movement is not a good indicator either way unless we've figured out how to drive GPS receivers down into the faults themselves and retrieve that information. I think they're just ground stations that are taking these GPS measurements, right?
What about the northern earthquakes? Do GPS stations up there report tiny movements in the crusts leading up to those earthquakes? I'm just curious if it's possible that you're dealing with different kinds of faults when comparing the San Andreas fault line versus the Ramapo fault line versus the New Madrid fault line.
What we’re learning is that faults switch on and off. They will be active for a thousand years or so, and then inactive for several thousand years. And then other faults may become active. From a scientific standpoint, that’s the really exciting thing we’ve learned from New Madrid. It has been the key to the door that opened up a whole new understanding about how faults inside continents work.
This sounds, at best, questionable or highly fitted to very recent events that we've had the privilege to watch. It's difficult to look over long swaths of time historically when our precision instruments for measuring are a very recent thing compared to the age of the crust. I'm not arguing for the spending of billions in the mid-west but I'm not sold on a single expert's opinion, is this consensus in the geological community?
My work here is dung.
Tectonic plate movement is exceedly slow, and rarely remembers anniversaries.
Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
But how could it forget? It was our diamond in raw form anniversary!
He who knows best knows how little he knows. - Thomas Jefferson
...for the release of cataclysm
Money would be better spent making a few places secure for winter time emergencies. Unlike California, if we're without power or housing, we die.
#fuckbeta #iamslashdot #dicemustdie
Step 1: Run outside and watch for falling corn kernels and cotton balls
He who knows best knows how little he knows. - Thomas Jefferson
you've invented an acronym that bothers me more than IANAL
My mind always reads that as "I anal", or in "I'm anal", Which makes sense if you're a lawyer meaning anal in the psychological sense, but it has certain sexual overtones as well that I don't want to think about on a website mostly populated by men.
Now you've invented an acronym for saying you're not a seismologist, IANAS, and my brain processes it as "I anus" or "I'm an anus."
Never mind why you have low self esteem: basically I just want to read about earthquakes and legal issues without thinking about so much goddamn anal and anuses.
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
The New Madrid fault is totally different from the faults in California. The earth in and around the New Madrid fault lines are covered with millions of years of river silt, clay, and other soft strata. It is several miles underground making observation of its activity difficult at best. The most observable activity is the sand boils. They usually indicate pressure pushing up to the surface. The faults in California are within harder, drier strata, making them much easier to see, even with the naked eye. The plates which make up the faults in CA also move with greater frequency causing the strata around them to be splintered with spiderweb cracking, making them easier to move when pressure builds up. The New Madrid fault doesn't move much because it is not along a significant induction/subduction area between plates like those in CA (though the plates on the coast are not actually diving under one another but rather rubbing against each other). This is why the last major quake at New Madrid was so large. There's very little movement to reduce the strain.
The theory of plate tectonics easily explains the earthquakes at the boundaries of tectonic plates due to the differential grinding motions of these plates. New Madrid is one of the 10%-15% of earthquakes that does not happen a current plate boundary, so its cause is less clear. There are motions of sub-blocks inside a plate. But these are typically an order of magnitude less that at established plate boundaries. So it may take millennia to build the same kinds of strains (20+ feet) it only takes centuries in a place like California. Geophysicists are divided by the amount of strain at New Madrid. Dr. Stein's group only sees a small amount in GPS data. Others see a lot more. The data has noise. Its quality depends on the experimental setup. The more stations you record, the more complexity you see.
The US government and university scientists are spending a lot of money and effort to understand the New Madrid area. It more a lack of understanding of intra-plate earthquakes than the amount of money spent. In this era of "no risk is too small" political correctness (e.g. TSA) perhaps no government authority is willing to demote The New Madrid risk as Dr. Stein claims.
(I was a classmate of Dr. Steins at MIT decades ago,)
I hate to break it to you Seth, but in every disaster movie I've ever seen, the guy who dies first (usually in an ironic way) is the scientist who says there's no danger and we don't need to prepare.
Support Right To Repair Legislation.
Seismologist (in training -- Ph.D. student), here.
The scientific and engineering consensus is that there is an earthquake hazard in the central US. New Madrid had three massive events at around ~M8.0 200 years ago, a dozens of M6.0 events, and there is paleontological evidence showing that these earthquakes have occurred every few hundred years dating back quite some time. The USGS gives the New Madrid seismic zone a 25-40% chance to have a M6.0 or larger earthquake in the next 50 years. I might note that seismic waves in this area travel significantly farther due to the older, less smashed-up ground underneath this region of the country. Additionally, the New Madrid seismic zone is filled with up to 1km of thick sediment. How, exactly, seismic waves propagate through thick sediment is still undergoing much study, but we do know that they focus earthquake energy, and studies in Taipei have shown that sharp velocity gradients in the sediment can double the peak ground acceleration of an earthquake at the surface.
Seth Stein and a few others in the GPS area look at surface measurements as the only sign for strain to build up causing an earthquake. This works with very pretty models of earthquakes, like near San Andreas and Eric Calais' famous "Haiti prediction" (he looked at the strain rates, calculated how much strain had built up since the last earthquake, and stated that if an earthquake were to happen soon, it'd be ~M6.8 or so), but it breaks down significantly for inter-continental seismic zones. The New Madrid seismic zone is one of those zones, and it is poorly understood. However, it doesn't take brain-busting thinking to entertain the idea that strain rate at the surface doesn't mean that nothing is happening at the subsurface, and, in fact, the New Madrid seismic zone has very frequent small magnitude earthquakes every day.
The scientific consensus is that the New Madrid seismic zone presents a serious seismic hazard based on tons of historical evidence and current seismological research. Seth Stein is the devil's advocate to that view and frequently and very public tells the world that there will never, ever be another big earthquake in New Madrid, ever. He is in the minority.
I might note that seismic hazard assessment for Wenchuan, China, was rated very highly in the 1950s due to historic evidence of horrible earthquakes in that area. Since the 1950s, the Chinese seismic hazard map has been revised several times and, due to very very slow strain rates measured by GPS, Wenchuan's risk of a catastrophic earthquake was downgraded to basically negligible. In 2008, however, we all saw that massive M7.9 that struck and killed so many people in this area where strain rates were "too small for a large earthquake."
I also might note that physicists at USGS have used the very same data that Seth Stein collected and used, and when they subtracted out the average movement of the North American continent, they found strain rates in the central US that were very high, more than enough to create a catastrophic earthquake. There is more than one way to interpret Stein's data.