Sennadar Forums

Need a little help, and I know you bunch are not only clever but read a lot. Trying to track down an article I read some years back that suggested possible causes of some midwest quakes. Gist was that the crust-mantle border wasn't flat but more like an undersea mountain range, only inverted with a few solid peaks descending down into the flowing areas. Don't think they phrased it quite that way, but they did suggest the quakes in that area (Dakotas?) had an especially deep spire that had been "plucked" or made to hum like a tuning fork by passing flows. Google and I have never been good friends, so fair odds I'm just not phrasing things right, but all I can think of are mixes of stuff like "midwest" "earthquake" "descending spire" or similar terms.

So, anyone familiar with what I'm talking about & where I might find some links to reference? Either to verify or debunk the idea?

Probably not the article your referencing but it seems close and some of the ideas are the same.
https://www.sciencemag.org/news/2016/09 ... arthquakes

The reason there are so many faults in the midwest-west is because the western side of the American tectonic plate has been pulled like taffy.

Most of the mountains in the west are called "Fault Block" mountains, which are caused by this action. The land pulls apart, parts of it subside and parts are pushed upwards, and bam, mountains.

This stretching is why many geologists believe that the American plate will eventually split and form two different plates, with a rift valley akin to the one in eastern Africa forming across the prairie states....in a few dozen million years.

You're likely right, Fel. All I can say is that what I (vaguely) remember referred to a section near the Great Plains the referenced experts thought should be stable, much like in the article Kacoo mentioned. [Thanks, friend!] Don't recall if they'd thought it was part of an ancient craton or not, but that would at least provide a reason for why they didn't just go with the usual tectonic plate logic.

However, I'm less concerned about the specific event (which might just be a false memory, for all I can recall) than what they proposed as its explanation: those descending spires of mostly solid rock. If such things aren't considered outright pseudoscience by the wider scientific community, looking to include it as part of something I'm working on. Apologies if I just made it more confusing, but I thought it might be easier to find the event than the concept.

It sounds like you're talking about the Lithosphere-asthenosphere boundary or the Moho (Mohorovičić discontinuity). The depth of the Moho varies from 10 km to 70 km and that is mapped using seismic tomography.

Glancing at the map on wikipedia, https://en.wikipedia.org/wiki/Mohorovi% ... continuity, it looks like the Moho isn't as deep under the Rockies as it is under the Andes and Himalayas. That might be related to the article you remember.

Yeah, one of those boundary-zone discontinuities, and fair odds you're pegged the right one, Isengrim. Knew I was forgetting a lot, but looks like there's even more I need to review for my project. Still, that might be roughly WHERE I'm looking for, but not WHAT; it's like me saying I'm looking for a kind of underwater landform (say a seamount or submarine ridge) and you're pointing me at the Benthic portion of the North Atlantic.

I know I started this mentioning stuff about the Midwest and Great Plains, and I apologize for being confusing; as my old friend Bester can probably attest, sometimes my words come out sounding more than a little alien and not the way I meant them to. I only mentioned the locations and circumstances because I thought seeking out the original article would be easier than tracking down this hypothetical geo-formation at the Moho. What I'm seeking is essentially the inverse of a magma plume: where the plume is a thread of liquid rock burning up into the rocky crust, this inverse would be narrow, semi-solid spine of rock drooping into the more-fluid mantle.

Hope that's a clearer phrasing. If not, don't worry about it, gang, this is just something I'm trying to put together on my own time, not a professional or academic obligation. So don't waste too much effort on me, was just trying to put some semi-solid science into my fiction.

If you want to get some education from an actual geology professor, here is a good one to look at, he has a lot of lectures online as part of a community education lecture series. Running from 2010 up to the present day(with a shift in format due to covid in 2019). Although as he is in Ellensburg, Washinton his focus is on the Pacific Northwest.

This one can start the process of melting your mind, even without the context of the prior lectures, you should still be able to follow it, although you might want to keep google maps handy:
https://www.youtube.com/watch?v=fibDx4CDNRc

The first about 38 seconds of this video illustrates some of what was talked about in the previously linked video. (also note, the second link was put on youtube about 2 years after the lecture, and starts about 30 million years after some of the earliest stuff he mentions)
https://www.youtube.com/watch?v=nS_lMsBdafI

Those were awesome.

I took geology in college as my science elective, and I found it absolutely fascinating. It very nearly tempted me to change majors AGAIN, but I stuck it out with Japanese.

I hear they have rocks in Japan. You could have done both.

Fel wrote: ↑Fri May 28, 2021 9:33 pm Those were awesome.

He really does a pretty good of presenting the stuff. He does wander around from time to time, but when he gets into presenting the supporting evidence, it's something else. Spent many, many hours watching a lot of those lectures, as I live in the Pacific Northwest and also did a semester of College level Geology myself he's very topical for me.

But that one was kind of fun. "This mountain in Washington's Cascade range, likely comes from where Mexico is today, and here is the supporting evidence" ... and oh, "based on chemical signature analysis, these rocks near Palm Springs, CA are also an (nearly) exact chemical match with our mountain in Washington" suggesting they formed in the same place at the same time, but parted ways millions of years before the San Andreas fault existed.

But yeah, that second animation.. The Plate tectonics theory has really started to have a number of really interesting curve balls lobbed all over the place since I was initially taught the stuff. The geologists clearly have evidence that the movements happened generally as indicated, but trying to explain the how and why on some of those plate movements has to be making a few of the geologists just going

That animated map now has me tempted to see if I can find someone who tries to tackle explaining what it was showing for that Santa Barbara portion of California 10's of millions of years ago, that just looks utterly bizarre.