Mere earthquakes. Thanks JimSEA.
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Posted on 12/19/2015 10:02:24 AM PST by JimSEA
Earthquakes in Idaho's panhandle are usually caused by the Earth's crust pulling apart. So why were earthquakes on 24 April pushing the crust together?
Last April, a swarm of earthquakes shook the ground near Sandpoint, Idaho. Unused to shaking, Sandpoint’s residents took notice. So did local media, widely reporting on the events. But it wasn’t the size or location of the earthquakes that surprised scientists.
Sandpoint lies along the Lewis and Clark Fault Zone, and previous earthquakes in the region were caused when the Earth’s crust pulled apart, which geologists call extension. But the earthquakes that struck on 24 April were caused by the Earth pushing together, Daisuke Kobayashi of the University of Idaho, Moscow, reported Monday in a poster at the 2015 American Geophysical Union Fall Meeting in San Francisco.
The Earth Pulls Apart
Crustal extension formed the region of the United States that stretches from New Mexico to California in the south and Utah to Nevada in the north and is known as the Basin and Range. In the southwestern portion of the area, abrupt changes in elevation—rows of steep mountains rising out of a flat landscape—characterize the terrain.
(Excerpt) Read more at eos.org ...
It's Global Warming!
Parts of larger plates move, spread and, in this case, change their orientation in relationship to other portions of their plates. They will collide and split apart according to stress and strain as defined in geology. Structural geology is the study of these movements.
There are 5 main concepts with which students struggle when thinking about stress and strain:
1. rocks deform,
2. stress causes strain and strain results in structures,
3. different physical conditions create different structures,
4. inferring stress from faults, and
5. the relationship between analogs and reality.
In this case the stress inferred from the strain and structure of the faulting indicate a “swirling” structure of rotation within the crust. Plates are not entirely independent of each other so a rotation within one plate impacts others. It may be expressed by different rates of subduction along a single plate edge. Thus, there might be a rotation of a plate or portion of a plate.
Ha!
Any info on depths? Thanks.
Sorry, no.
Thanks anyway. I might go back and dig through the data.
Let me know. From the article one would expect depths ranging from surface into the asthenosphere.
0.2 to 18km for San Point over the past 3 months, trending NNW/ESE.
Four to seven months ago, a series trending N/S with a 2.7 at 20km.
These have been pretty mild with the greatest at 4.3, 9km. Though they seem to indicate a fairly complex variety.
Some very shallow, some quite deep for a significant distance from west coast subduction.
Your map indicates a rotational setting semi-surrounding this array from E to NNE.
Seems an interesting paper could come out of it.
Thanks, I quite agree.
Mere earthquakes. Thanks JimSEA.
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