What’s the Deal with Quakes in East Tennessee? By Stephanie Osborn

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What’s the Deal with Quakes in East Tennessee?

By Stephanie Osborn

http://www.stephanie-osborn.com/

 

There’s been a lot of agitation and media reports (some legit, some less so) on the series of earthquakes in East Tennessee, and how this means the New Madrid fault system is about to go off again, and all kinds of stuff like that. Sarah and our mutual friend Jim W. and I have been discussing it, and I’ve been answering questions on social media and whatnot, so a quick tag-up with Sarah resulted in me sitting down to write this, to hopefully spread a little more understanding and lay some fears to rest.

So here’s the deal. According to the USGS, on 12 December, a magnitude 4.4 quake occurred near Decatur, TN. Epicenter location was 35.614°N 84.740°W, and it was about 9km (about 5.6mi) deep. OHMIGOSH! We had an UNPRECEDENTED quake in East Tennessee and it’s still rumbling!

So here’s a list of the quakes in the immediate area since the 4.4 quake (including the 4.4).

 

Magnitude Location Date
4.4 11km NNE of Decatur, TN 2018-12-12
3.0 11km NNE of Decatur, TN 2018-12-12
2.5 11km NNE of Decatur, TN 2018-12-14

 

But nobody even noticed that third quake! What’s up with that?

Well, it turns out that wasn’t all the quakes in the system, either. Here’s the rest of the quakes in the region for the last 30 days, as of 17 December, the time of this writing.

 

Magnitude Location Date
2.7 10km SW of Calhoun, GA 2018-11-23
2.7 12km NW of Sweetwater, TN 2018-12-08
2.6 4km W of Blaine, TN 2018-12-13
3.0 4km ESE of Mascot, TN 2018-12-16

 

Now, these quakes are not all clustered immediately around Decatur. But they are all along the edge of the mountain range, within ~100 miles or less of Decatur. But there’s something else important about them. They’re all magnitude 3.0 or less.

Why is that important? A 3.0 is just on the threshold of something that humans can even FEEL. Anything smaller than a 3, humans generally don’t even notice, and it must be detected by seismograph systems. Even many 3s go unnoticed, depending on location, underlying rock strata, building structure, etc. (Often they are completely unnoticed by those standing on the ground. Sometimes even larger quakes are unnoticed by those standing directly on the ground. I can speak from personal experience on this.)

So there were quakes going on in the area for some time (and likely longer than the USGS’ website is showing, since I’d have to request access to their database to go back earlier than 30 days ago, and that’s not going to be a quick process), and nobody even noticed, BECAUSE THEY WEREN’T BIG ENOUGH TO FEEL. (This is actually pretty typical of the fault zones associated with the Reelfoot Rift, as well.)

Are there any Reelfoot Rift quakes in that same timeframe? Well, sure.

 

Magnitude Location Date
3.1 9km NW of Tiptonville, TN 2018-11-22
2.9 9km NW of Tiptonville, TN 2018-11-22
2.5 8km NE of Pinckneyville, IL 2018-12-09

 

Note that the first two are squarely in the New Madrid Fault Zone, and the last is in the associated Wabash Valley Fault Zone.

OMIGOSH! They’re right! The East Tennessee quakes ARE setting off the New Madrid!

Well, no.

There were also quakes on the San Andreas, but nobody’s claiming the East Tennessee quakes affected IT. But it’s on the same tectonic plate! But there are no more structures connecting the New Madrid to the E.TN. faults than there are to the San Andreas.

Why?

Because the faults in the Appalachian orogenic zone are not only a long way away from the New Madrid system, they weren’t even created in the same era.

Many of the Appalachian faults are much, much older, and that’s one reason they’re largely inactive — the impetus to the original mountain-building/folding/faulting (this process is called “orogeny”) was the FORMATION of the Rodinia supercontinent (Appalachians 1.0, as some geologists waggishly make it, and they were likely huge) and the Grenville Orogeny, some 1,250,000,000-980,000,000 years before the present (YBP), due to the slamming together of tectonic plates. [Appalachians 1.0 are largely gone, eroded away by now.] The other sides of this orogeny — the other plates involved in the collision — include the Kibaran Orogeny in Africa (formed the Kibara Mountains in the Congo) and the Dalslandian or Sveconorwegian Orogeny in the northwestern (Nordic) part of Europe (now visible principally only as the Caledonian nappe system, which is a group of overthrust sheets).

The Reelfoot Rift, on the other hand, underlying the New Madrid and Wabash Valley fault systems, formed during the BREAKUP of Rodinia, some 750,000,000YBP. (For lots of information on this, I recommend my ebook, Rock and Roll, available for Kindle:

https://www.amazon.com/dp/B074SJ8ZPT

and Nook:

https://www.barnesandnoble.com/w/rock-and-roll-stephanie-osborn/1126973723?ean=2940158848162.)

The more recent orogeny (aka Appalachians 2.0), sometimes called the Appalachian or Alleghanian Orogeny, began during the formation of Pangaea, some 480,000,000YBP, again, due to the slamming together of tectonic plates. The resulting range likely reached heights comparable to the Himalayas! (By comparison, the Laramide Orogeny, which formed the Rockies, ran from roughly 80,000,000YBP to possibly as late as 35,000,000YBP, so they are MUCH younger and higher, due to having less time to erode.) Like the Grenville Orogeny, the other side of this collision formed the so-called Anti-Atlas Mountains of northwest Africa.

This makes the faults in East Tennessee thrust, or more properly, overthrust faults. A thrust fault is where the upper fault block (“hanging wall”) overrides the lower (“foot wall”). But the Free Dictionary defines “overthrust fault” as a geological term: “A low-angle thrust fault in which displacement is on the order of kilometers,” that is, a nearly-horizontal thrust fault.

Example thrust fault, Cactus Hills, Saskatchewan, Canada:

Note the roughly 45º angle of the fault.

Example overthrust fault, Glarus overthrust fault, Swiss Alps (red line denotes fault):

Note the virtually horizontal angle of the fault.

So. Between the faulting and the also-prevalent FOLDING of the Appalachian Mountains, if you stretched it all out, some scientists have estimated that Tennessee would be easily 1/3 to 1/2 again as long as it is.

Most importantly: Thrust faults, regardless of angle, are COMPRESSION faults.

But the Reelfoot Rift, the actual geological structure that causes both the New Madrid and Wabash Valley quake zones, is a TENSION/EXTENSION rift/aulacogen system. Upwelling in the mantle from a hotspot directly under the center of the Rodinia supercontinent (which insulated the mantle, CAUSING the hotspot), combined with the “conveyor belt” effect of the resulting convection, as the hot magma spread out, moved away, and sank back into the mantle, literally tore apart the overlying crust. (The Southern Oklahoma Aulacogen may have been associated with this same breakup, though other geologists speculate it may have formed during the breakup of Pannotia, another supercontinent, younger than Rodinia.)

So. This means that the two systems — the Appalachian fault systems and the New Madrid/Wabash Valley fault systems — have COMPLETELY different ‘modes,’ if you will, as well as different forms and times of origin. More, they are separated by some 300mi, with no real geological structures connecting them.

That said, it’s my personal theory that the tectonic plates do act (to a limited degree) as flat springs, which means that significant distortion at one side of the plate can produce stress at the opposite side; Jim and I have talked about this, and watched that stress ping back and forth from plate boundary to plate boundary in the form of very large quakes, for quite a few years now. So it’s just conceivable that stresses transferred from the shifting in East Tennessee (which is largely just rebounding from the last ice age, according to the geological studies I’ve read) could make themselves known in additional stresses on the multiple faults of the Reelfoot Rift.

But frankly, these East Tennessee quakes are NOT large, but pretty small quakes. Most of the quakes that are occurring are getting no attention whatsoever, because they are below the threshold of being felt. And even the largest, the 4.4, is generally considered a minor quake most places. I don’t really expect a whole lot of stress transfer from these. Translated, I don’t expect any increased New Madrid activity on their account.

So what’s causing them? Leftovers.

The rocks are most likely still slowly rebounding from ancient stresses, including the various continental collisions that created the mountains, as well as the dissolution of the giant ice sheets from the last ice age. (And those ice sheets are VERY heavy — yes, they even make the continents sag.) More, since all those ancient stresses are no longer being applied, that rebound is apt to be slowly tapering off with time.

Yes, the Decatur TN 4.4 quake was felt over a large area — for the same reason the big temblors on the New Madrid were felt from the Front Range of the Rockies, up and down the East Coast, up into Canada, and down into the Caribbean — the rocks in this region are cold and unbroken, and will transmit the quake energies long distances.

But that doesn’t necessarily mean that a true Big One is coming in East Tennessee, as there would be on the New Madrid or the San Andreas, because the stresses on those two systems still exist, but the stresses on the Appalachian faults are gone. And as I said, they aren’t likely to transfer any significant stress to the New Madrid.

So do what you need to do to stabilize your homes (psst — brick/masonry chimneys are especially vulnerable) and their furnishings against falling over in case there’s a few more minor shakes, then consider it the interesting geological event it is, and move on.

~~~

Check out Stephanie’s latest Division One novel, book 9 of the series, Head Games, now available for preorder in print and ebook, coming in January 2019:

Amazon: https://www.amazon.com/dp/B07L5ZMQFY?ref_=pe_3052080_276849420

BN: https://www.barnesandnoble.com/w/head-games-stephanie-osborn/1129706755?ean=2940161305140

Two galaxies will go to war—if Fox can’t save Chairbeing Entiyti from assassins.

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But when the belligerent Persis Federation arrives from the Andromeda Galaxy, the Ennead orders Alpha One on the tricky first-contact mission, hoping to avert intergalactic war. Unfortunately, the Persan premier chooses Omega as his newest concubine, leaving Echo trapped between love and morality, and duty and orders.

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9) Head Games

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79 responses to “What’s the Deal with Quakes in East Tennessee? By Stephanie Osborn

  1. I live in east Tennessee (a bit south of Knoxville) and we didn’t even know there had been an earthquake in the area until we heard about it the next day on the news and over the internet. A “big one” in east Tennessee? Yeah, I won’t be holding my breath waiting…

  2. BobtheRegisterredFool

    So the Great Old Ones buried beneath that part of America probably /aren’t/ stirring? We don’t have an urgent need to build giant boxing mecha? 🙂

    I appreciate the additional grounding in plate tectonics. Thank you.

    • We don’t have an urgent need to build giant boxing mecha? 🙂

      I think “That would be so cool!” fulfills the only reason anyone would urgently need to build a giant boxing mecha.

      • Yeah, but we do’t know for sure. Best to be safe and go ahead with the giant boxing mecha project. It’s for the children.

      • Reminds me – one of the Urusei Yatsura movies has a brief appearance by a giant robot that exists only to throw a fastball pitch.

  3. Just read Simone else saying these were not connected to New Madrid, but they were saying they thought a semi-major quake was likely on the Madrid, soon. But we’re rather vague about the meaning of “soon”.
    The biggest I felt in Texas, was iirc 4.4 or 4.3. I felt it well, as I was sitting in a small (10×20) metal stud, two story structure. The second story was a steel floor, with metal shelves holding half liter bottles of liquid. It moved, a lot. The only other person certain they felt it was a security guard, who was just standing against a wall. Everyone else was “What quake, where?” or “I thought it was just a truck going by”.

    I get people who look at me funny when I point out the land around the Great Lakes just did a rather fast movement, because of stresses from the Ice Age. I forget how much, but the top of the CN Tower is now several feet higher above sea level than when it was finished. Well the base is too, but there is a GPS sensor at the top.

    • The Oklahoma quake last year spooked people on the second and third floors of the hospital in Lubbock (150 miles south of me). Light-fixtures swayed and other moments of interest got their attention. I was half-asleep on the ground floor of a slab-foundation house closer to the epicenter and thought, “Huh, that’s odd. Earthquake? Earthquake. Cool.”

      • I felt several when I lived in Alvarado.

      • Roughly where was the OK quake? And what was the magnitude? Could have been along the Southern Oklahoma Aulacogen, or could have been related.

      • That response is largely how you determine just how long someone has been in California. If they’ve been there for a while, they’ve been through a quake or two, and ignore it so long as nothing’s falling down. Otherwise, they tend to panic when the ground doesn’t do what they expected it to do.

    • Yes, we probably are roughly overdue on the New Madrid, but nobody has a really decent periodicity for those — on ANY fault, really. So, yeah, vague.

      I’ve felt a 5.4 magnitude New Madrid quake. It was interesting. I heard it first, coming from the north, a distant rumbling growing closer. By the time it reached us, the whole house was shaking, and I could hear dishes rattling in the kitchen behind me. It was Saturday morning, and I was watching cartoons at the ripe old age of around 8, I think. I was sitting in the big armchair and had to grab the arms and hang on, lest I be thrown out of the chair into the floor by the movement.

      Mom & Dad were outside working, and they said they could see the house moving, though they didn’t so much feel it themselves. The house was a brick house and they could see mortar dust spalling away and drifting to the ground. When it subsided, they yelled at me to come to the back door, and made me come outside and spend the rest of the day outside.

      We used to regularly feel New Madrid quakes in the house where I grew up. Most of the time, “feel” wasn’t quite the right word. We’d be, say, sitting at the dinner table talking, and suddenly everyone would shut up and we’d stare at each other with a “what just happened?” expression, then somebody (it was usually me, because semi-observant scientist) would notice that the drinks in the glasses had standing waves, or the hanging lamp was swinging all by itself. And we’d know that there’d been an earthquake.

      Had I not gone into astronomy/astrophysics, I’d probably have gone into geology/seismology/vulcanology. I have an undergrad minor plus (meaning I had more than was required for the minor, but I figured rather than picking up ANOTHER science major I better get on to grad school) and a graduate subspecialty, in geology, as it is.

  4. This post is making phrases like “isostatic rebound” spring back into the forebrain.

  5. The basic problem with the panic-mongers is the delusion that ‘calm’ is normal. There are earthquakes all the time. There is volcanic activity all over the globe, more or less constantly. Storms are NORMAL. So are floods and droughts. The old dirtball just keeps on keeping on, with little to no awareness that we even freaking exist.

    People want things to be stable, which all too often means static. And it just ain’t gonna happen. I don’t really want to think about how much money, supposedly aimed at ‘environmental concerns’ gets wasted every year trying to keep beaches and barrier islands from eroding….which is basically what those formations DO. The enviroweeies wanted the forests in California to never freaking change, so they whined and lobbied and sued to make sure nobody ever cut down anything, or cleared anything, or controled-burned anything…..and now they have firestorms basically scortching the earth back to sterile, and making all the endangered species into meat charcoal.

    Back in the ‘80’s I read an interview in The Washington Times with a PhD in Meteorology fron Georgetown, who (among other things) said that at that time we were emerging from a period of historically unusually stable weather that stretched back to the beginning of Victoria’s reign. That we had gotten accustomed to warm in summer, cold in winter, and so on and that from written records going back to cuneiform that wasn’t how weather worked. So we needed to get used to thinking of snow in July and warm days in February, because fro what he and his colleagues could tell, that was what we were going to be seeing.

    Somethung to think about.

    • Oregon too. Just Oregon isn’t as likely to have communities in the way. Small coastal towns if you get another Tillamook like burn in the Coast range. Been a couple of big ones in the Cascades historically too, just don’t remember the names. Sisters, Bend, La Pine, & places like Sunriver & Black Butte, you’d hear about, because the more well healed have vacation or retirement in these areas. Then there are: Roseburg, Drain/Yoncolla/Elton, Canyonville, etc., but you notice I’m leaving out the big 3 (Portland, Eugene, Corvallis). Heck anyone remember the forest fires outside of Canyonville a few years ago. There were 2 the same summer at the same time. Know Days Creek got hit pretty hard, do you hear anything about that now? Still hearing about the CA fires from the same period …

      Let alone the fires in the wilderness areas we’ve had the last few years …

      • Darn it. Check the stupid box … darn it.

      • The almost-funny bit is catching the mainstream news hyperventilating over a 5.0ish earthquake On The San Andreas Fault!!!111eleventy!!!.

        And then in paragraph 3, they mention it’s by Hollister. Unsaid, or in paragraph 14 is that it’s the section of the San Andreas that’s not locked, and is prone to small-medium earthquakes all the time. (When I lived there, a 5.0 on a locked section of the SAF was noteworthy. It could be a foreshock. Maybe. Possibly. Sometimes.)

        Sigh.

        And, the worst fires in SW Oregon this year were in sections of wilderness that had burned before. I’ll skip the rant about blocking salvage logging and those trees adding fuel to the newer fires; just don’t let a greenie near me when I’m using a chainsaw. (Soon; had a big branch come down in a recent storm. Will have to dismantle it before I can mow that area come spring.)

        The rains this winter will make life far too interesting in the burn scar areas. Not much to hold the soil, and we’ve had some really rainy events already. Whee.

      • I went camping in the Deschutes near Bend with some friends some odd years after that fire, and the very soil was ashy. I came back from that camping trip with all my clothes (and exposed skin) charcoal gray.

    • Remember these are people who think they can centrally plan and control everything, such as economies, climate, and now apparently earthquakes too. Of course the real reason for the hype, aside from pure clickbait to drive traffic, is the desire of leftists to end fossil fuel use. Watch how quickly you see the usual suspects blame extraction of fossil fuels for the quakes and cite them as a reason that fossil fuels must be banned immediately. The fact that their claims have no basis is irrelevant, they are simply trying to manufacture a narrative to achieve their long desired goal of totalitarian control over society.

      • They seem to me to be getting increasingly desperate. Maybe they know that the coming big solar minimum is going to kick the chair out from under their global warming narrative. Or maybe they’re running smack dab into the fact that too many of their Dire Warnings have proved wrong over time, amd too many people remember. Maybe they thought that eight years of Obamaramadingdong were going to be enough to kill off fossil fuels and get everybody into battery powered go carts. Most of them live in congested areas, so they have little grasp of how much of the country is out of range of one battery charge of even the best battery buggy. And they have no grasp of history, so the idea that electric cars date back to 1884, and are not new technology with a lot of potential for rapid development is beyond them.

        And of course they just nominated The Smartest Woman In America and enough people reacted to it by saying, in essense, “She’s a leather lunged, lying bitch who should probably be in prison. No way do we let her in the White House” that Her Shrillness went down in flames. They hold everyone but Their Wonderful Selves in contempt, and it is beinning to dawn on them that the feeling just might be mutual.

        • Those electric cars must be fed electricity, which is supposedly going to be generated by free clean renewable sources like solar power (except no filling the desert with mirrors!) and wind power (but windmills kill birds!) and tidal power (It spoils the view and kills fish!) and hydroelectric power (dams are bad for rivers!) and the like. (Like, what, specifically?). It is somewhat ironic that all the proposals for energy sources beloved by environmentalists are, when you get down to specific projects, opposed most vigorously by environmentalists.

          I would love to be able to not depend on finite sources of fuel indefinitely, but if the numbers for supply and demand and timing don’t work, using the force of law isn’t going to make them work.

      • All of the coal mines in TN are well north of Decatur, in Claiborne, Campbell, and Knox Counties — in other words, up along the TN/KY state line. You’re looking at a distance of AT LEAST 80+ miles to the NEAREST mine.

        There is some drilling for natural gas and petroleum, but the majority of this is also along the KY/TN state line, to the N and NW of Knoxville/Knox County. (Overton, Fentress, Pickett, Morgan, Clay, Jackson, Scott Counties.) The main exceptions to this are Cheatham County (NW of Nashville), and Loudon County. Loudon County is SW of Knox County, and the near side of the county line is something like 12-15mi away from Decatur, whereas the Loudon well is on the far side of the county.

        There are evidently many drillsites in TN, and this includes areas relatively close around Decatur, but I gather from some extensive google-fu that the counties I’ve listed above are the only ones that are really doing much.

        So…yeah, no.

    • More, we don’t really WANT the planet to be static. Static, in this instance, would be very bad. The very fact that the planet is constantly reshaping itself in all the ways you mention is what maintains it as a place where life can exist, and will CONTINUE to exist. That might seem bizarre, but it is the truth of the matter.

  6. Christopher M Chupik

    Orogeny? Is that anything like orgone energy? 😉

  7. Donald Stephens

    There are always the ‘overwrought’. They’re just graben for attention by invoking New Madrid.

  8. IIRC Tennessee wasn’t squashed down by glaciers during the last ice age. Rather, it was pushed UP due to the ice pushing down on the crust north of where the Ohio River is now; much like a giant sea-saw; or dough being flattened pushing up everywhere you’re not pushing down because the material flows away from where you’re pressing it. Any quakes from isostatic rebound should be as the ground settles downward.

    • I can confirm that the farthest position south that the glaciers got in North America was in Posey County, Indiana. Nothing got beyond the Ohio River.

      • Ah, possibly. Possibly as far south as Kansas or southern Nebraska. The data were a little conflicting the last time I looked into the subject (ten years ago.)

        • By way of reference, Posey County, Indiana lies about a degree south of where I-70 runs in Kansas.

          • That’s where the data are messy. Is there evidence of glaciation as far south as Wichita, possibly Arkansas City? Or is it just north and along I-70? Or only in Nebraska, if there? *sigh* It would be nice if the Magic Geologic Eight-Ball were clearer.

            • There have been a number of glacial advances. The first four documented were named after Wisconsin, Illinois, Kansas, and Nebraska. Later study revealed that some of the glacial deposits assigned to one “stage” were from more than one advance.

              The continental glaciers diverted entire rivers and the Missouri and Ohio rivers of today flow relatively near the point of maximum advance. Any river which flowed north was blocked by the glaciers. Lakes formed in ice-dammed valleys until they spilled over into the next valley east or west, connecting new segments of formerly separate rivers. Then the glaciers began to melt and retreat, and the huge amount of meltwater mixed with debris eroded the new river valleys deep enough to prevent the rivers from resuming their old courses.

    • The trick to understanding glacial rebound is to remember that it is all attached — one big chunk of crust. Note I simply said it was rebounding. It doesn’t matter which direction it is rebounding; the point is that it IS rebounding. And the northern end of the Appalachian orogeny certainly WOULD have been pressed down. The surrounding regions, even if not under the ice sheet proper, would have felt the stresses involved.

      So in this event, the transfer of stresses is a leeetle bit different; because you have a big slab of rock, with another big slab of ice sitting on top of it, the entire contiguous slab of rock is going to experience the stress of carrying all that weight to some degree.

      Transferring energy from fault to fault, I believe, CAN be accomplished in a similar fashion, as I mentioned in my original post. But to directly transfer considerable energy from one specific fault to another specific fault tends to require a structural connection more direct than simply, “They’re all in the same hunk of rock.”

  9. In california, when you see a hill around LA or SF, it is telling you something shoved it up. I grew up in Berkeley. The road cuts in the hills east of town show recent sediment laid down flat, now looking like waves. So the hills are alive, it is just the time scale is not ours.

    At a recurrence rate of 500 years for a magnitude 9, in a million years there are 2,000. Looking at a map of california, it reveals how the shifting interaction of the plates has produced the bay, LA’s steep hills, the Mohave plateau, the caldera explosion of the Bishop Tuff a million years ago, and the uplift of the south Sierra. The earthquakes make sense as the stresses build up, and then the rock breaks.

    We should be glad for the earthquakes. They are a sign that plate tectonics is still working.

  10. Sigh… you guys know nothing. Clearly the evidence shows that it isn’t “Earth Quakes”. Yea right! IT’S THE GROUND SON IF IT MOVED ALL ON IT’S OWN, THE GOVERNMENT WOULDN’T LET YOU PUT BUILDINGS ON IT! DUH!!!

    Clearly there is a Titan buried, sleeping under TN, and all this is just flatulence. If you keep on making “Earth Quake” jokes, don’t blame me when the Titan wakes up grumpy because he thinks you are making fun of him!

  11. I think one of my ceramic profs said that the Uwharrie (sort of) Mountains east of Charlotte, NC are remnants of Pangea or is it Rodinia?

    (And am I suppose to be seeing pictures? I can see tables, but not pictures of faults.)

  12. When I lived in Albuquerque, I saw a chart of the earthquakes in the area. During the time I lived there, 20-30 occurred every year. Most of the time the only way I even noticed was the water in the toilet moving around.
    Albuquerque is in a rift valley the sides of which are still moving apart. A little father south the quake frequency is higher.

  13. I have been a bad girl. I completely forgot today was Wednesday, when Sara said she would post this. I’m sorry, guys; the hubs is sick, and my mind was on other stuff. I’m here, and will go through and answer questions as I can.

  14. Drat. The illustrations of the thrust faults and overthrust faults didn’t “take” in the article.

  15. Perhaps it is the last part of the URL (after the question mark). Maybe without it WordPress will work magic?

    • Thank you.

      You can see the various strata just above the snow, how it lies at a relatively shallow angle. Look at the delineation between the dark strata of the rugged peaks and the slightly lighter, browner strata below them. That delineation is the overthrust fault. The material on top literally rode up and over the material on the bottom.

  16. Deep time. When I was growing up, the first 4 billion years of earth was lumped into a “here be dragons” Precambrian era. You could just skip over it, as prelude to the interesting story of life when creatures started building shells and bones.
    It is amazing how much we have learned since 1950. We have learned so many ways the universe can kill us. Yellowstone, we thought this a pretty mountain valley with water features. No clue of how dangerous the caldera was. Off Washington and Oregon, no idea that the ocean comes to visit every so often with a 9 earthquake.

    I have wondered related to Tennessee earthquakes, if the New Madrid system extends north and south. The alluvium dropped by the Mississippi would hide any records. Imagine a magnitude 8 earthquake near New Orleans on a 2,000 year cycle. What other things don’t we know?

    • Let me strongly recommend this book, then:

      I spent considerable time tracking down how far the whole rift system extended. The gist of it is that the Laurentian plate (what became the North American craton) did not extend that far at that time. The “continental shelf,” if you will, was slightly arched, but the northern extremity of the “Gulf of Pre-Mexico” was around mid-eastern Arkansas, which is the limit of the Reelfoot Rift, as pretty much verified by seismographic studies. That gulf, the Reelfoot Rift, and the Southern Oklahoma Aulacogen together comprised the triple-junction rift in the Rodinia supercontinent that eventually opened when the Kalahari plate, and later the Rio de la Plata plate, tore away from the Laurentian plate.

      Pretty much the entire state of Louisiana, and a significant portion of Arkansas and Mississippi, are “add-ons” (Mississippi Embayment) due to the sediment deposit of the River proper — extended delta, if you will.

      • Nitpicking a bit-

        The Kalahari and Rio de la Plata were somewhere in the mix, but the (current) Argentine Precordillera was probably the Rodinian piece which separated last in this region. The Precordillera rocks have a history which is a good match for southern Laurentia of 500+ million years ago. It is thought that this continental fragment separated along the Alabama-Oklahoma transform 515 million years ago. The Reelfoot Rift is truncated at the south, the Oklahoma Aulacogen at the east, and they may have connected at one time but the evidence rifted away.

        Following that event there were multiple island arc collisions leading up to the assembly of Pangea. This created the Appalachians and Ouachitas. The breakup of Pangea created both the Atlantic Ocean basin and the Gulf of Mexico. The basement there (Louisiana, Mississippi, southern Alabama) is composed of extended crust from the island arcs, covered with sediment. The Mississippi River would not have formed until the Gulf Of Mexico appeared, and before the Pleistocene Ice Age it was a smaller river, as much of the interior drainage flowed north and east.

        • Thank you. I was having a hard time finding the exact plate fragments that separated away from that specific region. In the end, I looked at the general maps of the breakup and extrapolated.

          The point being, that was the edge of the Laurentian plate, and thus the Reelfoot Rift doesn’t extend any farther on the current North American plate as such. There may be a continuation elsewhere, but it would be on a different plate.

  17. I would like to thank our Gracious Hostess, Sarah, for not only inviting me back to talk about this earthquake question so soon after the solar discussion, but for adding in all those lovely purchase links! She had told me to add my latest book, which is book 9 of the series and in preorder, so I added a list of the books in the series to this point, and she added the links to those! I’m having a lot of fun writing the Division One series, and I hope my readers are enjoying it, too!