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+--- Thread: Mechanism Behind “Strange” Earthquakes (/showthread.php?tid=301)
Mechanism Behind “Strange” Earthquakes - Skywise - 08-31-2015
http://universityofsoutherncalifornia.cmail2.com/t/ViewEmail/j/6ECCB8AEDEB2C844/643D5669AEA0F77733C48669A65BFAC1
Scientists Discover Mechanism Behind “Strange” Earthquakes
Ran across this elsewhere.
The thing is, how is this a new theory? I've always heard this was the explanation for these kinds of quakes.
And what's this about mountains wanting to flatten out? Never heard that before, and it doesn't even make sense. Not to mention, where's the geologic evidence of mountain ranges flattening out?
Has my brains felled out?
Brian
RE: Mechanism Behind “Strange” Earthquakes - Island Chris - 09-01-2015
Hi Brian,
actually, I found the article interesting: I should read the published paper. You could be correct and I could be wrong, but I had not heard that mantle convection was linked to intraplate (within plate) quakes. This could be a big deal to earthquake hazard mapping (except, as the author stated, it is not the last word). New Madrid is not accumulating strain, yet it is a huge bulls-eye on the USA hazard maps. There is a debate on whether the seismicity there is just aftershocks from 1811-1812, or is it likely to have more M7+ quakes in, say, the next 500 years.
Also, they are correct about mountains spreading out and collapsing, except of course it is not that simple. Indeed, there is a lot of extension including normal fault earthquakes in Tibet. There are gravitational stresses that make mountains want to do this. But, there are tectonic forces that keep some of them tall. Oddly, erosion also can make mountains taller: you remove mass in the valleys by erosion, and isostacy makes the rocks uplift, and the ridges that eroded less become taller mountains. Not sure of the latest research, but the Rocky Mountains may have become taller and more rugged in the last 2 or 3 million years due to climate change (towards colder=ice)
Chris
Chris
RE: Mechanism Behind “Strange” Earthquakes - Skywise - 09-01-2015
I dunno. Maybe I had heard it as a proposed idea some time ago and took it as writ. Or maybe I intuited it on my own not realizing that wasn't accepted theory. Or misremembered. All I know is that when I read that press release I was thinking "Yeah? What's so novel about that? I thought that's the way it worked anyway."
Regarding mountains, disregarding all other forces I can see how there would be a tendency for the weight to want to crush the mountain over time, a looooong time. But it seems to me other forces would overwhelm this process, particularly the forces pushing the mountain upward. Yes, gravity makes things that go up want to come down, but that 5 million pounds of thrust rocket engine just isn't going to let that happen. I wonder if there's any old mountain ranges that have spread out that I can spot in Google Earth.
As for the normal faulting, I thought that was caused by the compressional uplifting of the range, not any relaxing spreading.
Hmmmm.... maybe I need to go back to school?
Brian
RE: Mechanism Behind “Strange” Earthquakes - Skywise - 09-01-2015
(09-01-2015, 08:04 PM)Skywise Wrote: As for the normal faulting, I thought that was caused by the compressional uplifting of the range, not any relaxing spreading.
Hmmmm.... maybe I need to go back to school?
Yeah... back to school... I'm confusing normal with reverse.
Brian