Possible cause

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Posted by Ballpark Frank ( on 09:29:23 06/16/17

In Reply to: Earthquake Near West Yellowstone posted by Jilly


I am not near the park at present. I'm down in Colorado, but will be back in Montana late tomorrow, so I have no experiential information on damage reports or feeling tremors. According to the Associated Press, it was felt in West Yellowstone, but there were no reports of damage.

The refined data from the USGS shows the magnitude adjusted downward to 4.4, at a depth of 9.3 km. The relatively shallow nature of this temblor, along with the location (13 km NNE of West Yellowstone) suggests that it is likely related to a long term geological phenomenon that has been reported by Dr. Bob Smith and others from the Yellowstone Volcano Observatory. They noticed subsurface movement of hydrothermal fluids toward the NNW from the vicinity of the Mallard Lake resurgent dome, which commenced a decade or more ago. I am not current on that movement, so I don't know if their instrumentation continues to detect that flow. When Bob Smith lectured in Bozeman on the subject about 8-10 years ago, he described a slow gradual movement that was going from a higher to a deeper place beneath the Earth's crust, roughly heading from near the Old Faithful area to beneath Purple Mountain, which is just north of Madison Junction. The epicenter of this latest moderate quake would be somewhere north and west of Purple Mountain, maybe west of Mt. Holmes somewhere. (I haven't researched the exact location on a map.) I'm thinking this quake may have resulted from subsurface lubrication of "basement rocks" by hydrothermal fluids flowing into the area under pressure. This would be somewhat similar, in terms of causation, to what various locales are experiencing in other parts of the U.S. attributed to fracking. Back in the 1960s, there were earthquake swarms in the northwest Denver suburbs, that were eventually attributed to two high pressure wells at the Rocky Flats plutonium warhead plant, north of Golden. Those wells were used to force atomic waste deep underground. Once the wells stopped operating, the quakes gradually dissipated, eventually stopping altogether.

I'm providing a link to a useful USGS web page that shows graphically the results of reports submitted online by folks who felt the subject quake. You can see it was felt as far north as Bozeman, and probably at Chico Hot Springs and over in Ennis.


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