Earthquake followup
August 30, 2011 8:37 PM   Subscribe

Seismic waves propagating across the US --- "Phil Plait showed the spectacular animation of seismic waves propagating across the US from the 5.8 Virginia earthquake last week, but left out part of the story. A commenter, davenquinn, picked up some details."

" If you look at the video you see an enormous number of sensors in the Midwest and Great Plains....."

More at Robert Grumbine's blog
posted by hank (19 comments total) 32 users marked this as a favorite
that is super cool.
posted by LobsterMitten at 8:43 PM on August 30, 2011

When I took an earthquakes & volcanoes class (aka, Shake & Bake) in Ann Arbor, they showed us their seismograph that was linked to a location in Ohio and told us a story about an odd pattern of vibrations they kept registering. Five days a week, early morning and mid-afternoon. It turns out the sensors in Ohio were up the road from a trucking depot.
posted by bentley at 8:44 PM on August 30, 2011

Derailing from Bentley's comment, back when I was doing undergrad research, I spent a lot of time listening to seismic and infrasonic signals.

Although they'd been using a variety of techniques to track down and pinpoint things like earthquakes, rockslides, and the sea(!!) for ages, one of my colleagues developed a much better algorithm to spot big booms occurring in close proximity to our sensors.

Thereafter, I spent a good portion of my summer looking for tiny blips in our signals that the algorithm could pinpoint to a nearby location, and then riding my bike out to various locales in Fairbanks, Alaska to figure out exactly what the heck was making big booms, and shaking the earth. (Also, they wanted to make sure that the algorithm worked. )

There were a few interesting ones... mining charges being set off, heavy road construction, a ceremonial military cannon, a housefire where a propane cylinder detonated....and a gazillion tiny blips in the middle of the woods. After puzzling over this one for well over a month, another colleague happened to spot my map full of pins, and asked me why I was looking at flight patterns. Eureka. Turns out that the "thunk" from an airplane lowering its landing gear is actually extremely loud on frequencies that are inaudible to humans, but were easily picked up by our microphones several miles away.

So, yeah. I'm in favor of covering the planet with every kind of sensor imaginable, if only because it allows us to spot unexpected stuff like this.
posted by schmod at 9:05 PM on August 30, 2011 [35 favorites]

I love the Bad Astronomy blog. It's on my everyday reading list, and has been for years. Thanks for posting this, because while I saw it when it was posted, BA is such a part of my life that I rarely think to make a MeFi post out of stuff I see there. Good show.
posted by IvoShandor at 9:16 PM on August 30, 2011

Which programs/agencies that fund the kind of exploratory sensing you're talking about, schmod? When I was in grad school it was basically impossible to fund anything that wasn't hypothesis-bound with a clear outcome. Personally, I wish there were more such work being done and more money available to do it.

The video reminded me strongly of this video of gamma radiation from fukushima washing over Europe.

Country-scale sensing ahoy!
posted by fake at 9:21 PM on August 30, 2011 [2 favorites]

You can see those types of videos for many more earthquakes here. Warning: you can spend a lot of time being fascinated by them.

I highly recommend the ones from large, far-away earthquakes. Check out, for example, the recent 8.9 in Japan. The phase labelled R2 on the seismic trace below the animation, the one that's two hours after the original earthquake, where the waves appear to be traveling in the opposite direction to their original direction of travel? They're doing exactly that, because they're the waves that went the other way, around most of the Earth (on the surface, not taking shortcuts through the middle), to arrive from the other side. Which is awesome. And, I think, gives you a sense of just how long this energy keeps bouncing around.

You can even see that on a much smaller earthquake like this one, a 7.0.

So yeah, EarthScope is the coolest.
posted by mandanza at 10:13 PM on August 30, 2011 [5 favorites]

Stab in the dark as to why Texas has the subsequent waves while the rest of the midwest becomes still: Oil / gas reserves? Being more liquidy (or, rather, being rife with pockets of liquid and gas) might explain why there's more bouncing afterwards compared to the more solid parts of the country. IANAG(eologist).
posted by shen1138 at 10:56 PM on August 30, 2011

Seismographs around Portland recorded the Virginia quake.
posted by Cranberry at 10:57 PM on August 30, 2011

posted by chemoboy at 12:59 AM on August 31, 2011

I like how the Mississippi delta quivered like a bowl of Jello long after the initial quake.
posted by Gungho at 4:17 AM on August 31, 2011

" If you look at the video you see an enormous number of sensors in the Midwest and Great Plains....."

That's because the real no-shit serious fault in the US is in the middle of the country. Meet the New Madrid Seismic Zone. BTW, remember the rule that in this part of the country, everything was named by the French and mispronounced by everyone else, that's MAD-rid, not ma-DRID.

The real cause, though, is that (roughly) the East Coast is going east, and the West Coast is going West. Rivers run downhill, and notice the Mississippi, running almost due north-south through the Midwest. Notice how *low*, compared to sea level, this valley is.

This is a nascent rift zone, where the continent is pulling itself apart. See also the Midcontinent Rift. Others: The Upper Valley of the Rhine, aka The Rhine Rift, a very advanced once, the Gulf of Suez, the Bay of Fundy, and the famous East African rift.
posted by eriko at 5:03 AM on August 31, 2011 [5 favorites]

I thought it was the New Madrid Fault too, but no:
These are areas not known for seismic activity, so what are they doing with so many sensors? They are part of a travelling array (the 'transportable array') of seismometers, part of the Earthscope initative from the National Science Foundation.

The idea is to have a substantial number of seismometers moving stepwise across the US every few years. Then, having a dense array of seismometers, particularly to have them in places that we don't normally, will show us things that we don't normally see.
posted by DU at 5:14 AM on August 31, 2011 [2 favorites]

Fucking socialism.
posted by Threeway Handshake at 6:21 AM on August 31, 2011

BTW, remember the rule that in this part of the country, everything was named by the French and mispronounced by everyone else, that's MAD-rid, not ma-DRID.

Why would the French name a place after the Spanish capital?
posted by Sys Rq at 8:09 AM on August 31, 2011

I would like to see more data in the band between Southern California and Louisiana, particularly Arizona and New Mexico. It looks like a lot of reflected noise occurring throughout the SW US. The thought of oil bearing substrates struck me as well, but who knows?
posted by Xoebe at 11:08 AM on August 31, 2011

Yes, DU's quote is correct. The TA (transportable array), that very dense block of stations, started on the west coast and has been slowly migrating east over the last few years. After it finishes up in the lower 48 it'll move to Alaska. Everyone in the seismology community is pretty excited to see what it'll tell us about the New Madrid Seismic Zone but that's not the sole purpose of it by a long shot.

Eriko, do you have any citations for that explanation for the NMSZ? My understanding is that the fault zone is there from the last rifting event that separated the Americas from Europe and Africa, related to a failed arm of that rifting event, the Reelfoot Rift. All of the U.S. east of the Colorado Plateau is very stable and no part of it is really moving relative to any other part. You can see that on this map from UNAVCO, which is a plot of GPS motion vectors relative to "stable North America." You can see that, yes, most of the West Coast is moving subtly away from stable North America, but that extension is accomadated by the Basin and Range in western states such as Nevada.

For more on failed rift arms, see, for example, the Wikipedia page on failed rifts, and the one on triple junctions. Rifts tend to (or maybe even always?) form with three arms, such as the Red Sea/Gulf of Aden/East Africa rift. Triple junctions like that are not stable, long-term; one of the three arms always dies out, leaving a zone that is heavily faulted but no longer active, unless stress reactivates a fault, as in New Madrid.
posted by mandanza at 11:25 AM on August 31, 2011 [2 favorites]

the East Coast is going east
[The Mississippi Valley]This is a nascent rift zone, where the continent is pulling itself apart.

No -- my understanding is in line with mandanza's, namely that the East Coast is not going east, and the Mississippi flows in a failed rift zone, which was active a long long time ago -- it's not a nascent/currently active rift. The Wikipedia link to "midcontinental rift" agrees with this.
posted by LobsterMitten at 11:44 AM on August 31, 2011

Seconding mandanza's skepticism of eriko's Wikipedia interpretation, recent research has shown that the NMSZ is not as dangerous as previously thought.
posted by hyperizer at 1:51 PM on August 31, 2011

Stab in the dark as to why Texas has the subsequent waves while the rest of the midwest becomes still . . .

It's because Gov. Perry wasn't there to keep things under control [rimshot].
posted by Man with Lantern at 12:30 PM on September 1, 2011

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