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View Full Version : Earthquake waves are polarized? Used for a Volcano Eruption Detector



Ara Pacis
2013-Apr-09, 06:55 PM
here (http://news.yahoo.com/volcano-burps-reflected-earthquakes-150424984.html)


Johnson went back to the 2008 records from Kilauea's seismometers, instruments that record earthquakes, and examined how the seismic waves traveled through different underground rock layers. Earthquake waves can split similar to the way light passes through polarized sunglasses and they'll travel faster along layers than across layers, Johnson explained. Cracks in the rock layers can also change this "polarization" as the voids open and close in response to changing forces, such as Kilauea's growing and ebbing magma chambers. [Amazing Images from Kilauea's Lava Lake]

Before the 2008 Kilauea eruption, an increasing amount of gas forced its way through fissures and cracks in the volcano's summit lava flows, and the changing stress affected how earthquake waves traveled through the rock layers, Johnson discovered. Johnson looked at the changes in the earthquake waves, a technique called earthquake "shear wave splitting," and was able to link them to the rising gas levels, something that has never before been done at Kilauea.

Something new or old hat?

dgavin
2013-Apr-09, 07:25 PM
New science, but from reading article it still sound like gas monitoring is still the best way to predict an eruption. This would be useful in area's where it's difficult to get gas monitoring equipment into.

It also appear to take atleast 4 seismographs to detect the shear wave splitting.

So while it is new, and could add to detections in some cases, volcanoes that don't have gas monitoring.

grapes
2013-Apr-09, 10:01 PM
Something new or old hat?
If you just mean the use of polarized earthquake waves (the title of the thread), that is pretty old.

The wiki article says the use was over thirty years ago, I thought it was before that, but that's before my time. :)

http://en.m.wikipedia.org/wiki/Shear_wave_splitting