Rock and Roll: The New Madrid Fault System Part I: A Geology Primer – By Stephanie Osborn

Rock and Roll: The New Madrid Fault System Part I: A Geology Primer – By Stephanie Osborn

Rock and Roll: The New Madrid Fault System Part I: A Geology Primer

Excerpted from Rock and Roll: The New Madrid Fault System, ©2017

By Stephanie Osborn

Images in this article are public domain.


This whole collection of writings started off with an email exchange, months ago. Our illustrious hostess was part of the discussion, and expressed interest in my converting the info to one or more blog articles. Then, when the LibertyCon programmers heard about it, they asked me to give a presentation on same, which I did.

The presentation was a full house, and at the end, there was a request for me to convert it to blogs and/or an ebook. I asked how many would like to see an ebook of the material; virtually every hand in the lecture hall went up.

A little over a month later, with additional research under my belt and factored into the manuscript, the book has gone live. And as promised, I am providing Sarah a series of blog articles on the subject. This series of blog articles is only a small fraction of the material contained in the ebook; it may be considered in the nature of a series of informative abstracts of the information contained therein. For additional information, may I recommend that you check out Rock and Roll: The New Madrid Fault System.


Part I: A Geology Primer

The New Madrid Fault Zone is the core of a large area in the central USA consisting of a couple of main faults and numerous secondary faults, as well as other significant geological structures and features. It produced an historic series of severe quakes in the winter of 1811-12 timeframe, and it continues active to this day.

The New Madrid Fault Zone is located in the central United States, roughly along the medial segment of the Mississippi River, from about Memphis, TN running north to at least the confluence with the Ohio River. There are strong indications that the fault zone extends considerably farther in each direction, though exactly how far remains in doubt.

Now let’s define some basic terms, so everyone can understand what’s being said when I dive into the meat of the discussion.



A fault is a crack in the rock around which the rocks actually MOVE. Stress fractures can occur in rocks that are experiencing non-moving stresses, such as temperature extremes, but these are NOT faults. Only if one or both of the stone blocks on either side of the fault experience movement is the fracture considered a fault.

The surface direction or trend of the fault is known as the strike. The vertical orientation of the fault is known as the dip. The importance of a fault’s dip lies in the fact that the actual source of the quake may not be directly under the part of the fault that shows at the surface.

A quake is generated if the fault has been unmoving for a prolonged period of time, with the cessation usually due to friction between the crustal blocks, and stress has built up sufficient to either exceed the “coefficient of friction” (a physics term characterizing the amount and type of friction between surfaces) between the fault blocks, or to actually shatter the rocks that are hung up on each other. At this point, the temporarily-stationary blocks “slip” past each other, releasing potentially tremendous amounts of energy in an earthquake.

The point where the slip begins is the hypocenter or focus, and it will usually be below the surface of the ground. The point ON the surface, directly above the hypocenter, is known as the epicenter. So the pertinent data to identify any given quake are: the magnitude, the latitude/longitude of the epicenter, and the depth of the hypocenter.

Not all faults, of any sort, will generate quakes, let alone major quakes. Some faults, or segments of faults, tend to experience slow, small, continuous movement called creep. This creep can cause slow deformation of structures on the surface, but will not cause widespread damage.

There are three principal kinds of faults, though there can be combinations. These basic types depend on the direction of movement of the fault blocks on either side of the actual fault.


  • The normal fault.

In a normal fault, the main block aka the “hanging wall”—the block above the fault—moves down relative to the secondary block or “footwall” which is below the fault. Such faults are created under tension forces, and movement is produced as a result of continued tension. If the tension is removed, the fault ceases to be active.


  • The reverse, or thrust, fault.

In a reverse fault, the main block or “hanging wall” moves upward and over relative to the secondary block or “footwall”, which may remain still or move downward and/or under. Such faults are created under compressive forces, and movement is produced as a result of continued compression. If the compression is removed, the fault ceases to be active.


  • The strike-slip fault.

In a strike-slip fault, the blocks move past each other in a horizontal motion. Such faults are under slight compression, mostly in a transverse fashion, meaning the forces are across and at an angle relative to the fault.


  • The oblique fault.

An oblique fault combines horizontal and vertical motion in various fashions; it is basically a strike-slip fault with either normal or reverse faulting added in, depending upon whether the overall forces combine to produce tension or compression.


Grabens and horsts

Put in everyday language, grabens and horsts are fault-block hills or mountains (the horsts) and valleys (the grabens). They are formed when several parallel-trending or nearly-parallel normal faults alternate dips (downward angle of the fault), which will in turn result in alternating uplifted and/or down-dropped blocks of stone. Usually the sequence of fault blocks is under tension (extension) in a direction perpendicular to the strike trend, causing them to spread apart, and enabling alternate blocks to slip downward.


Types of molten rock

Molten rock is generically termed “melt.” If the melt is below the surface, it is magma; when it has extruded onto the surface, it is lava. Any rock formed from cooled, solidified melt, regardless of location, is igneous rock.



A pluton is a magma intrusion into existing rock. It may intrude into existing rock in any of a number of ways: between different rock strata (layers), where the change in rock layer produces a localized weakness; into cracks in the rock, whether a joint or a fault; into areas of collapse, such as a caldera or sinkhole; or by melting/eroding away the rock and incorporating it into the melt.

Types of plutons include:

  • Volcanic magma chambers
  • Batholiths—These are, for all intents and purposes, “failed” volcanic chambers where a vent never reached the surface. Some were originally buried quite deep. They are essentially giant “bubbles” of magma that cooled and solidified over eons.
  • Laccoliths—These are large “bubbles” of magma that, unlike the more vertical batholiths, are usually inserted horizontally, between existing rock strata; they tend to be lenticular, or lens-shaped. Over time, they, too, cooled and hardened.
  • Sills—These are narrow horizontal intrusions, usually following a horizontal fault, joint, or other crack. Being relatively thin, they cooled and hardened fairly quickly on geologic scales.
  • Dikes—These are narrow (but often long) vertical intrusions, typically following a vertical crack or fault. Other than spatial orientation, they are similar to sills.

    similar to sills


To obtain a copy of Rock and Roll: The New Madrid Fault System by Stephanie Osborn, go to:

120 thoughts on “Rock and Roll: The New Madrid Fault System Part I: A Geology Primer – By Stephanie Osborn

  1. Morning science, awesome. I have been looking forward to this series. Book is on my wishlist now.

    1. $3.99 Kindle edition on Amazon.

      Now the only thing I need is a reader with neutral buoyancy in air so I can stop dropping it in the sink or other aqueous places of dubious nature.

      1. Issue isn’t the cost. The issue is my backlog of “need to be read” is far too long currently. 🙂

        1. Ziplock bag. Seriously, go with the brand name, because they’re pretty darned reliable on keeping the kindle dry in the bath, where the house brands may not be. But they’re thin enough to be able to page turn, and yet water (and soap) proof enough for accidental dunkings.

          Or you could spend a lot of money on an otterbox, but ziplock works for me. 🙂

          1. And the freezer bag type of ziplock uses heavier plastic so should be better protection.

          2. I’ve been thinking about getting an otter box for my tablet, but not for water-proofing reasons. I have seen my 3-year-old daughter drop the thing on concrete, and another time I have picked it up and noticed a gap between the back cover and the front. I have a funny feeling that zip lock bags aren’t going to be sufficient to prevent damage from such mishaps.

            I had no idea that the thing can protect my tablet from accidental dunkings into water, though…

  2. I like it. A Geology refresher with details about the New Madrid System. I studied Geology as an undergrad, many years ago, but don’t know much about this fault system. I look forward to the rest of the posts and am also getting the ebook.

    1. I got to take some geology courses in college years ago, in part because they got me out of a classroom. Born and raised in California, we mostly got used to the occasional shaker (lived 11 miles from the epicenter of the ’89 Loma Prieta ‘quake, which was quite sporty, I assure you).

      Now we’re gone from California, up in central Minnesota, as I cross the Mississippi four times each day going to/from work. And thinking about the New Madrid now and then, and wondering just how anything built up here with no concern for earthquakes whatsoever might be affected the next time it cuts loose.

      Got the book, just the thing for lunchtime reading…

      1. Once, for a series of meetings out from St Louis, we were given instructions for what to do in the event of an earthquake, and what to do in the event of a tornado. So, there’s a real possibility of a two-fer: an earthquake during a tornado.

  3. A quick clarification request:
    Are they now using reverse fault and thrust fault interchangeably, or is a thrust fault still a subclassification of reverse fault (that is, a reverse fault with a low angle of dip).

    1. If you’re a geologist, by and large a thrust fault is a sub classification of reverse fault. If you’re a geophysicist working with seismic data (though you may use them interchangeably depending on your audience they tend to understand ‘thrust fault’ better than ‘reverse fault’). Engineers in the oil business may differentiate or may just use them interchangeably. To most other people it ranges between ‘interchangeable’ to ‘You mean there’s words for that?’

      This is my own experience for the current state of terminology in industry.

      Side note: We had a really cool survey in a very faulted region. You could see the sub-surface horsts and grabens (not always actually hills, the terms refer to the actual blocks). One graben was especially clear. Amazing plunging syncline. And that was just the most dominant feature of the region.

      1. All of this.

        In places like the Rockies, the horsts and grabens become obvious (although much of the Rockies system is a series of parallel faults with the same kind of fault, aka tilt-block mountains), but in other places, horsts and grabens can be hidden. In our case, the horsts and grabens are buried under literal miles of silt.

        I did have some illustrations in the blog article for the different faults, and horsts and grabens, but unfortunately apparently WordPress delenda est.

        1. I wish I had permission to show the seismic sections we processed. My co-worker and I were geeking out over how clear the faults were. Refraction statics were… interesting… since several of the faults went clear through to the surface.

  4. Walter Jon Williams had a fun/interesting “what if” novel set in the world as the New Madrid fault let go, and then the major story was dealing with the aftermath. IIRC, it was called “The Rift.” I wonder if I still have that on my bookshelf? I’m gonna have to go look when I get home tonight.

      1. And upon seeing your recommendation I checked into it and bought and read in one sitting. I’m glad it was three day weekend to me time to recover. I’ll read it a few more time but now I can read it a bit at a time and not stay up all night. Maybe.

  5. To our excellent guest blogger: Thank you very much, I enjoyed this. I look forward to the future installments.

    Sadly this does does remind me of all the precious time and opportunities I wasted when my ‘job’ was to learn and someone else was underwriting my education.

    I did get to pick some of it up again when it was The Daughter’s job to learn such things, which was nice side benefit of home education.

    1. I’m glad you enjoyed it, and I’m glad you’re continuing to learn, too.

      FWIW I do find that I understand this sort of stuff a lot better now than I did when I was in school. I think it has to do with experience in my various fields, and seeing how stuff works together.

  6. Question! I know this isn’t about the New Madrid fault, but is a cooled laccolith when exposed by erosion what forms a monadnock?

    1. Not really.
      I mean, it conceivably could, but any erosion resistant formation can.
      IIRC, volcanic plugs are the most common source for a variety of reasons (including the slope naturally leading away from them, bring more resistant to erosion than extrusive igneous rock, the relatively unweathered state of the rock, and the naturally vertical emplacement). But I’ve seen some features with a quartzite cap that could qualify.

      1. Thank you.

        I am rather familiar with Pilot Mountain, the inspiration for Mount Pilot of The Andy Griffith Show fame. The mountain stands by itself in the upper Piedmont, south of the Sauratown Mountains (of which it is considered to be part) and east of the Blue Ridge. What makes it truly noticeable is the quartzite monadnock formation on top, the ‘pilot house’ from which it got its name.

          1. The big Pilot House formation used to have a staircase, but now it is off limits to climbing. We are told that this is because of nesting ravens, which may be.

            I am sure that liability issues <never entered anyone’s head. not.

    2. Nibbled from various Wikipedia articles.

      ‘Structurally, Mount Monadnock (in New Hampshire) is part of an overturned syncline, a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than 2 km (1.2 mi)[1] or 5 km (3.1 mi) above a thrust fault from its original position.’

      Mount Monadnock gets a LOT of hikers each year; and the number of unprepared ones, and ones that get lost, seems to get larger and larger each year.

  7. Dr. “Santa Claus” Sam Romberger would be proud of how much of this I remember from GE101 lo these 29 years later.

    1. I was having a mild flashback to 1) the sea of freshmen surrounding grad student me in PhysGeol 102 (there was no 101), and 2) some of the geology guest lectures at Flat State that I attended. They’d let anyone wander in off the sidewalk if you behaved, even *gasp* historians.

      1. That makes me think of the last big hike on last year’s vacation, Chimney Rock at Capitol Reef. We reached the trailhead just behind several vans full of college students from a flat state. They were at the trail for a geology/physical geography scavenger hunt, trying to locate various instances of various types of physical features.

  8. The presentation was a full house, and at the end, there was a request for me to convert it to blogs and/or an ebook. I asked how many would like to see an ebook of the material; virtually every hand in the lecture hall went up.

    If you persist in pandering to public demand like this you will never become a legitimate author, and no “real” publisher will want you.

  9. A few factoids for all y’all,
    We delivered a total of seven New Madrid blog articles to her Highness which she confirmed to have received, but in her rush to start her French vaca did not tell us when they were scheduled to appear, so today’s post is a complete surprise.
    Steph is a night owl so eventually she will notice and then jump in and answer your questions.
    RES, I know the legitimate author crack is a joke, but even with more than 30 books in print Steph still gets that comment or something very similar on a far too regular basis. It was a long hard struggle for me to convince her to take the latest series indie because of remarks like that.

    1. As proud possessor of several of those 30 books (in print, not phosphor dots) I trust Steph will understand that the point of the jest was mockery of those defenders of privilege, the American Publishing Houses and their sycophants in the Mainstream.

      Legitimacy is not conferred by editors and publishers but by readers, those nasty folk who insist on reading what they want rather than what they’re told to … and who are the ultimate source of payment for that pleasure.

      1. Well, RES, I’m still working on building up the fan base to something that’ll bring in royalties sufficient to pay bills. (No, all authors are not jet-setting wealthy people like Jessica Fletcher or Richard Castle. Some of us struggle to make ends meet.) And I’ve caught some serious flak on the subject, including some very nasty little remarks from some, shall we say, names — even for having books with small press, never mind indie. Uncle Lar is aware of some of it, but not all by any means. i have never been possessed of an especial amount of ego or self-esteem, though my somewhat reserved nature (I’m actually kinda shy) seems to make people think I am very egotistical. So such things tend to hit hard and deep. I don’t usually show it, because my dad’s side of the family is very Victorian English, so stiff upper lip and all. But it’s there.

        1. …I suppose, were I actually making a comfortable living off the writing (for those who don’t know, I’m handicapped and early-retired as a partial consequence), it might not hit so deep. As it is, there are days when i wonder why i keep on keeping on.

        2. Well, if you see or hear any such comments made even semi-seriously, rather than in mockery of said comments, just show ’em your middle fingers and tell them that attempting to tear others down to make themselves look better is what bullies do, and that bullies are the kind of thing that needs to be scraped off the bottom of the shoes.

          1. Hon, I have anxiety disorder. I am intensely uncomfortable with confrontation. I have never used the middle finger gesture in my life. That scenario ain’t happenin’.

            1. Regardless, anybody twit enough to utter such a thing is saying far more about themselves than about you. Publishers are not, and never have been, in the business of selling “good” books; they’re in the business of selling books that sell “good.” So what if you haven’t received the same imprimatur of official approval as Harold Robbins, Jacqueline Suzanne, Erich von Däniken or Hillary Clinton?

              Yeah, money can be nice, but it is important to remember its cost.

              1. “Yeah, money can be nice, but it is important to remember its cost.”

                Yes. But I never said I wanted to be rich. I just want to help heart-patient hubby pay the bills and offload some of the stress from him.

                Rich is nice, though as you point out, it has its drawbacks. But I’ve never been rich, and don’t really have much of an interest in going there. I would be quite happy with an income sufficient to pay my share of our bills and allow hubs a breather now and then. Do I have that now? No. Might it be that this year the whole book-writing/promo thing might actually break even for the first time? Maybe. I’m working on it, at least.

                Help me out by telling all your friends about my books, and writing brief reviews of them on Amazon.

        3. i have never been possessed of an especial amount of ego or self-esteem

          Fortunately for you, that’s an area where I haven’t had much of a problem. From where I’m sitting, having bought your books, you are in fact a real author. Anyone who says otherwise is contradicting me and is therefore obviously wrong.

          1. Oh, that was never an issue, really. It hurts, but I know it isn’t true. The question becomes how many other people may believe it, and how does that impact my sales? And since my sales are not over-large as yet, it does become painful.

            I’m serious: the best way y’all can help is to help me grow my fan base. Tell your friends — even if they don’t read SF, they might like some of my stuff, because of the high level of mystery, etc. I tend to put in my books. Pop over to Amazon and leave a review if you liked my books. It doesn’t have to be fancy. Hit the right number of stars, then say something like, “I really liked this book. I’m looking forward to the next one.” These are the kinds of things that would help increase my sales, help me pay the bills, and ensure that I can keep on writing no matter what may happen in future.

        4. Stephanie, I’ve been told I’m a “has been” even while still publishing more than the people calling me that. Also, if I have the temerity to show my art in public I get told I’m trying art “because your writing won’t sell.”
          A living — well, I make what I would make as a secretary or an assistant professor.
          Giving up — we ALL consider it. All of us who aren’t GRRMartin. Who has given it up but is still getting paid.

          1. Politeness prevents me from expressing my opinion of Georgie Martin. I watch the HBO shows, T&A and gratuitous violence don’t you know, but I’ve never felt compelled to wade my way through the books. Those who have tell me that as with most book to screen translations media eventually veers far afield from the original text as we’ve all seen in other examples of book to movie or TV.
            As for a living income from writing, such is relative. I’ve been helping Steph out with a bit of business and financial management advice, and we’ve been feeling blessed that with five new books up or in prerelease in 2017 we just managed to break even for the year a couple of weeks ago. The equivalent of a secretary or assistant professor salary is a dream well beyond reach at the moment.
            Things like these articles do seem to give sales a boost, and thanks to you Sarah for the venue, and your fans for their support. Still, if we cannot figure out the magic formula to expand the fan base sufficient to generate a decent income from writing Stephanie will have no choice other than to seek some position that will hire an over educated middle aged handicapped female. At which point for the most part the books would of necessity have to stop.

            1. I haven’t seen or read any of Martin’s stuff, because the subgenre isn’t my cuppa. So I have no opinion one way or the other.

              As for the rest of it? Yes. So much this.

              I love writing. I love the worlds, the characters, I create. I don’t want to have to stop. But bills have gotta be paid, and the hubs can’t do it indefinitely, not any more. His own health won’t let him. (I know, when you see him at conventions, he looks fine; I’ve been told he looks better than I do…and he does, I know. And he feels fine. But he’s a serious heart patient, and it takes an effort; he just doesn’t show it.) So I gotta do what I can. But (and this is for those of you who know the spoon theory) I just don’t have enough spoons any more, myself, to do a day job AND still manage to write, if it comes to that.

              There was a time I could work a whole day at the office, then come home and write until 1-2am, go to bed, get up and do it all over again. But that time has long since passed, I’m afraid. My usual reaction to arriving home after a 3-day convention is to crash and sleep for several hours, then get up and eat dinner, go to bed at “normal people” hours or even early, and sleep until my usual getting-up time (“normal people” lunch) and try to resume my regular schedule. My reaction to attending DragonCon is to come home in a good deal of pain and crash for nearly 24 hours, then promptly develop a severe case of con crud and stay in bed the rest of the week. (This despite regularly taking my flu shot, which normally wards off con crud. Happens every time. And it’s why I don’t do Dragon every year; I can’t afford to, either financially or health-wise.)

              So I am very thankful to Sarah for her eagerness to let me guest-blog here on my science-y stuff. And I am most thankful to her readers, and to my own readers — y’all — for supporting me as much as you do. I’m sorry I’m asking you to do more, but the strongest fan bases are grown organically, from what I’ve been able to tell. And that means y’all spreading the word. Tell me what I can do to help you, to encourage you, to motivate you, and I’ll be happy to do it.

              And again…THANK YOU.

            2. if you won’t, I will…

              He needs to take some time to do a little more research into some matters before voicing an opinion on it.

              If he can’t do that, maybe he should actually write books for that series instead of dragging his feet for six years.

              1. Time, I can see. I’ve “only” been published 8 years.
                Volume? I have 35 books I’ve authored, co-authored, or to which I’ve contributed, with more on the way. How much more volume is generally considered necessary? I’m averaging 4+ books a year now.

      1. How yah doing Frenchie girl?
        Wasn’t worried about you until I saw that Steven Green was also vacationing in France. Do not let that bad man lead you down a path to temptation. And if you do those Riviera beaches remember the prime rule, pictures or it didn’t happen.
        And yeah, it’s a particular sore point with Steph, she’s been “schooled” by certain know it all types at cons about how small press is just indie under a different name. All while she is in fact a Baen author with a collaboration with Doc Travis, has series with two well known small publishing houses, and at long last the new series under her own label.

                    1. I will remind The Spouse that I have the annual celebration of another pass around the sun coming up.

        1. “Do not let that bad man lead you down a path to temptation.”

          I can think of worse people to follow into temptation than Mr. Green.

    2. I haven’t had the pleasure of meeting Ms. Osborn yet, but she seems to have a quirky sense of humor that appeals to my own.

      1. I do indeed have a very, ah, inconvenient sense of humor, prone to coming out at all the wrong times (judging by the number of times I bloodied my lip to keep from cracking wise during NASA meetings, or else laughing at some inadvertent and often unrecognized pun someone else made), and look forward to the opportunity to meet.

  10. My first job out of college was with Geotech Corp, monitoring seismic data. Pre-deluge, of course.

    1. I greatly enjoy geology, particularly seismology and volcanology. I’ve prowled around as many volcanoes in the PacNW as I could get to, and had I not gone into astronomy, might well have gone into one of those fields.

  11. Further developments and comments, as I’ve tagged up with Stephanie.
    She is out of pocket at the moment, a rush editing job on a short story for an author who’s name I won’t mention, but eventually she will respond to questions.
    I thought the post looked a bit lean and she confirmed that WordPress seems to have eaten several graphics that were in the original article. May be my fault as they passed through my hands in transmission. But I got Stephanie to promise to post a link to the full articles with illustrations at some future time. There should be an image associated with each bold dotted header in the article. She did confirm that the full text was present though.

      1. an’ WordPress have our issues at the best of times. I got one blog where we take turn about posting, and it’s reached the point where I have to write my article, then let someone else post it, because it simply balks whenever I try to do it. No matter what I do. Now, there’s other WordPress sites that don’t give me problems. But 9 times out of 10, I just wanna nuke it ’til it glows, then shoot it in the dark.

    1. …I just realized that WordPress actually modified some of the formatting I’d done, also. So, for instance, “Grabens and horsts” should also be bolded and bulleted, in addition to having an illustration, and it has none of that.

      WordPress delenda est!

  12. So speaking of, is the San Andreas a strike-slip fault complicated by it not being straight?

    1. Yes, the main fault is a strike-slip fault. The region is very broken, so there are numerous secondary and tertiary faults, some of which are normal, some reverse, and some strike-slip. But the actual plate boundary is a strike-slip.

      1. …at least in the California area. In the PacNW, the plate boundaries are overthrust faults with subduction zones. Think of the Pacific plate as not only translating, but rotating a little about a vertical axis, and you can maybe see why.

    2. Don’t apply your binary preferences to it! The San Andreas fault can be whatever orientation it wants to be! 🙂

      1. I just got the statewide memo: The San Andreas Fault has chosen to identify as a Sea Cucumber.

        Take note.

  13. Allan Danzig’s story “The Great Nebraska Sea” comes to mind. It was in Galaxy and has been anthologized.

    And I’ve long thought that somebody should name a newly discovered earthquake “Not My” or “Someone Else’s.”

  14. Hey guys, just so you know, I’m here, I’m around, but I’m playing catch-up on my own writing after yesterday’s fast edit job for a fellow author. I have the comments set up for email notifications, and I’ll answer as soon as I can if you post a question, but I’m not going to keep the blog up continuously in a tab today. (I did, yesterday.)

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