Posted on 03/11/2008 3:19:18 PM PDT by blam
Earthquake activity is frozen by ice sheets
11 March 2008
NewScientist.com news service
Can you put a freeze on earthquakes? It seems so, according to a computer model showing that earthquakes happen less often in areas covered by ice caps. Trouble is, quakes come back with a vengeance when the ice melts.
Andrea Hampel at Ruhr University in Bochum, Germany, and colleagues wondered why Scandinavia experienced a surge in tectonic activity around 9000 years ago, whereas few earthquakes occur there today. They realised that the earthquake flurry coincided with the melting of the Fennoscandian ice sheet, which blanketed the area in the last ice age.
To discover why, they devised a model to test how geological faults respond when buried beneath several hundred metres of ice. They found that the vertical stress placed on the Earth's crust by a heavy ice sheet can suppress many types of fault from slipping and causing a quake.
Though the faults are pinned down for a time, stresses in the crust continue to build, so when the ice melts, earthquakes occur more strongly and more frequently (Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2008.02.017). This has already been been observed in Alaska, says Hampel. She warns that Greenland and Antarctica could experience more earthquakes as their ice sheets disappear.
From issue 2646 of New Scientist magazine, 11 March 2008, page 17
(Excerpt) Read more at environment.newscientist.com ...
We know that to be a fact at the end of the Ice Age.
Coincidence? I don't think so.....
Musta been that there global warming 9000 years ago that made the ice melt.
Yeah, that’s the ticket.
Say... maybe we finally have a workable solution for San Francisco...
How active is the Canadian shield. I would assume it to be pretty active since it’s still rising after the last ice sheet retreated.
However being seismically active doesn’t mean major earthquakes. It can mean nearly undetectable constant tremors.
This actually makes some sense. The underlying formations are squeezed a little tighter due to the massive weight of the ice cover, which should make it somewhat less likely to shift like they’d like to.
The ancestors of the Vikings had SUVs. Who knew? They were probably justified, because really, how else can you transport your pet wooly mammoth?
Maybe the melting of the ice was caused by the heat generated by magma movement associated with the earthquake activity? They can’t blame it on American SUV drivers though...
Or... When water is frozen on the surface, it can’t seep down and lubricate the fault?
No, that’s really not it, since ground water won’t seep down that far to where these faults actually break loose.
If that were the case, we wouldn’t be seeing major earthquakes occurring below the sea floor, and we do.
Compression and release of the crust is probably gradual enough that few big quakes would happen. It’s not like horizontal crustal movement that builds up and builds up and has to release in the same direction.
It's been known for a long time that uplift of the crust took place in glaciated areas when the enormous load of the ice was removed (it's called isostatic rebound). I suspect that was the cause of the quakes.
Water is slightly more dense than ice so man-made reservoirs must have the same effect. We should build more dams in California. By shifting water between two reservoirs it is likely possible to massage out near-surface earthquake tension completely.
Except that reservoirs are a fairly small footprint over a faultline, whereas an icesheet can cover thousands or millions of square miles.
I don’t know if it’s true or not, but the Oroville, California, earthquake of the early 1970s was suggested to have been caused by the building of the dam there.
My guess is that it’s more likely to have been a coincidence, but I’m not sure we could ever know.
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Thanks Blam. |
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LOL — thanks for a good chuckle. I needed one.
In the shadow of the Moon
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Posted on 08/31/2004 11:42:25 AM EDT by SunkenCiv
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