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Quake swarms warm up Butte monitors Yellowstone seismic activity jumps sharply in June By BARBARA LaBOE The Montana Standard BUTTE - Mike Stickney is always monitoring Montana earthquakes, but he's been busier than usual lately. An earthquake swarm near West Yellowstone has meant Stickney, director of earthquake studies for the Montana Bureau of Mines and Geology, has been recording several small earthquakes a day, though none have been of any great magnitude. About 600 earthquakes have been recorded since the swarm started June 13. A swarm, Stickney said, is a series of small earthquakes unrelated to one large quake. "It's just a very chaotic group of earthquakes that tumble in on top of each other," Stickney said from his office on the Montana Tech campus. "So there's a lot going on in a short period of time." Scientists don't know the cause of earthquake swarms, but Stickney said they're typically nothing to worry about. "They're generally not significant in terms of human safety, but you never know with earthquakes," he said. The latest swarm seems to have hit its peak around June 16 and 17 when Stickney recorded 21 earthquakes in the Yellowstone area. The numbers have dwindled to about two or three a day now, and all are of small magnitude. The largest in this swarm was 3.8 on the Richter scale, possibly large enough to be felt though officials haven't received any calls. Swarms happen in the Yellowstone/Hebgen Lake area about once a year. The largest occurred in 1985 when there were thousands of earthquakes for six weeks. The largest earthquake in that swarm was 4.9 on the Richter scale with several over 3.0, Stickney said. The earthquake studies center was established on the Tech campus in 1980 and has been recording and tracking earthquake data since 1982. There are 31 sensor stations around the state that report any earth vibrations back to Stickney's office via radio waves. His computers are also tied into the National Earthquake Center in Colorado which allows Stickney to gather information from sensors all over the region. Scientists still are unable to predict earthquakes, but the data Stickney is collecting allows scientists to begin to make estimates on the frequency of larger earthquakes. Tracking all earthquakes in a region over many years also allows scientists to predict what areas are most likely to experience a large earthquake, he said. While the current swarm doesn't appear to be anything substantial, Stickney said it is a reminder that southwestern Montana is seismically active area and could experience a large earthquake at any time. "The northwest corner of Yellowstone and Hebgen Lake is probably the most seismically active area in the lower 48 outside of California and Nevada," he said. "So we see small earthquakes every day." From 1920 to 1960 the state averaged an earthquake of 6 on the Richter scale or larger every 10 years, but has now gone 25 years without even an earthquake of 5 on the Richter scale. "And we don't know if things were unusually active back then and this is more normal or if we're in a clam period and the active phase is normal," Stickney said. "So there's certainly the potential here for a large earthquake and I think it's going to catch a lot of people by surprise. "We've had whole generations grow up without a major event here and we have a lot people moving into this region with no idea it's seismically active," he said. "There's quite a few people here unaware of the full potential."
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