Scientists studying Yellowstone NP earthquake clusters
Posted: Nov 4, 2013 by MTN Meteorologist Matt Elwell
WEST YELLOWSTONE - Western Montana and Yellowstone National Park are certainly no strangers to earthquakes, but this summer several clusters of earthquakes were raising the eyebrows of scientists.
This past summer marked an event that in many respects was normal around Yellowstone National Park - earthquakes. But, there was one exception - the sheer number of earthquakes that shook the area.
Nearly 130 small magnitude earthquakes occurred between Sept. 10 and Sept. 16 with different epicenters around the park - these clusters of earthquakes are known as swarms.
"Earthquake swarm is swarm in indeed a cluster of earthquakes without one large outstanding event," Director of Earthquake Studies at Montana Tech, Mike Stickney said.
"Earthquake clusters kind of come in two flavors," he added. "One is a main shock-aftershock sequence where the main shock is a big earthquake followed by smaller earthquakes that typically die away with time."
"A swarm is just is a bunch of earthquakes without any outstanding earthquake. You get numerous earthquakes with similar magnitude in that sequence of events," Stickney said.
The rumbles that hit Yellowstone in September fall into the second category. "They were actually very dramatic swarms if you were looking at seismograph centered near the epicenter of those earthquakes,"Stickney explained.
"There would be two, three or four-minute earthquakes going off every minute. Most of those were tiny magnitude one or smaller earthquakes," he continued.
And what's more - visitors to the park may not have even known it was happening. "Depending on how excited they were about the animals they might not have even noticed the earthquake," Stickney said.
He says that there are fairly logical explanations, and one of them isn't necessarily that Yellowstone's volcano is roaring back to life.
"There is good evidence to suggest that as magma, the molten rock at depth, cools, and crystallizes, it releases volatile water and gasses and those make their way out through fractures in the earth to the surface we see those as geothermal features in the park," Stickney told us.
"That fluid migrating through the earth's crust, we can think of that as lubricating some of those fractures and can produce some of those earthquakes. Probably those swarms in Yellowstone are related to the overall volcanic activity at depth and not necessarily indicating that something is getting ready to erupt," Stickney said.
Stickney pointed out it could be quite the opposite - the volcanic activity might just be quieting down, and those swarms may be just the result of gasses being released.
Stickney says that scientists know of about 75 faults around Western Montana that show evidence of seismic activity and only a handful of those faults have been studied in detail.
Scientist hope to be able to study them in more detail to understand how and why those faults might move.
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