Monday, August 8, 2016

Alaska earthquake "swarm" probably not earthquakes at all

ANCHORAGE (KTUU) Earlier this summer, the scientists at the Alaska Earthquake Center began monitoring a swarm of small earthquakes in an area about eight miles west of Mt. Spurr. According to State Seismologist Dr. Michael West, they probably aren’t earthquakes at all.
Hundreds of small seismic events have been registered in the area since June 11, with almost 100 of the recordings exceeding magnitude 2.
“That catches our attention,” says West, “because magnitude 2 is big enough that you’re being recorded, you can see that signal a few hundred kilometers away.”
The three possible sources of these seismic events, according to West, are standard earthquake activity, volcanic activity or glacial activity. “The patterns of all these little events didn’t fit the pattern of a classic earthquake swarm driven by stresses, tectonic pressures in the region,” says West. The Alaska Earthquake Center worked with the Alaska Volcano Observatory and largely ruled out volcanic activity. That left glaciers as the most likely explanation.
“I have to be clear, there is no smoking gun right now about exactly what these are,” West says. “The hypothesis of least astonishment I think is that they are probably coming from one of the glaciers in that area.”
Most “glacier” quakes are caused by large icebergs calving into water. West says some of these can be felt hundreds of miles away. Glaciers can also cause the ground to shake from crevassing, grinding against the underlying rock and pieces falling off ice falls. “If you’ve ever stood near a glacier, it’s a noisy place to be,” says West.
This particular swarm is near Pothole Glacier and swarms have appeared in this area as far back as 1985. According to West, swarms have occurred in 2010, 2012, and 2014 as well as this year. “This year's swarm appears to be the most vigorous to date,” says West. The swarms tend to happen between June and September. “These are the warm months. This is the time of year when glaciers are at their maximum. This is when they are moving fastest,” say West. “Glaciers sort of come alive in the summer then hibernate, tend to move a little more slowly, tend to be a little less noisy in the cold months.”
Though these small earthquakes don’t do any damage, seismologists watch them carefully. West says sometimes small earthquakes indicate the location of larger faults or they can warn of a possible volcanic eruption. “In this case, all signs suggest it is just another one of Alaska’s noisy glaciers,” says West.
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