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Mike_Gauthier

Minor Earthquake

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there was a minor earthquake near the summit today. here is what the USGS guys had to say about it... there notes were very brief...

The following is our notification message about the larger of several earthquakes, which took place at Mount Rainier today. There was one at 10:07 PST of Mag=2.5 also plus a number of much smaller events. We are keeping an eye on these. They are located at shallow depth directly under the summit. They have the characteristics of regular tectonic earthquakes, NOT volcanic earthquakes.

A MINOR EARTHQUAKE OCCURRED AT 10:42 AM PST February 19, 2002 THE MAGNITUDE 3.2 EVENT IS LOCATED 0.9 Miles N of Mt Rainier, WA THE HYPOCENTRAL DEPTH IS 0.0 MILES

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quote:

Originally posted by Mike Gauthier:
They have the characteristics of regular tectonic earthquakes, NOT volcanic earthquakes.

Can anyone give a resonable explanation of the difference between tectonic and volcanic earthquakes? Does it have to do with the depth of the origin? Just curious... and wasting time! grin.gif" border="0

[ 02-20-2002: Message edited by: max ]

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quote:

Originally posted by max:

Can anyone give a resonable explanation of the difference between tectonic and volcanic earthquakes? Does it have to do with the depth of the origin? Just curious... and wasting time!
grin.gif" border="0

[ 02-20-2002: Message edited by: max ]

In a nutshell:Tectonic earthquakes are quakes associated with boundaries between tectonic plates, commonly called faults. Movement along these faults due to variable plate movement produces tectonic earthquakes. Volcanic earthquakes are produced due to changes in the stress of solid rock caused by movement of magma into and out of the magma chamber beneath a volcano or as a result of magma moving into cracks in the surrounding rocks.Volcanic quakes do tend to be shallower.

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"volcanic" quakes tend to be shallower, and are more localized and generally of much lower magnitude because they aren't due to big stress releases from intra or intercrustal movements like last years quake in Puget Sound. Quakes associated with magma movement tend to come in swarms and have a harmonic signature. You can really see this in some of the seismograms from just prior to the St Helens eruption(s).

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I lead with my mouth in the last blurb so here's a correction - by "volcanic" the USGS folks probably mean quakes associated with magma movement. I was thinking in terms of any quake associated with a volcano whether it be due to magma movement or fault slippage.

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