A brief, but robust earthquake swarm shot the monthly seismic totals for the Yellowstone region over the 250 events per month mark for the first time since October, 1996.
The earthquake swarm began June 10 with a 54-event/day seismic burst centered about 5 miles west of Norris Junction. It included a moderate M4.5 jolt at 7:35 p.m. and several in the M2-M3 range. Activity slowly decreased to 9 events/day on June 13 and then surged again on June 14, producing 34 events during the day, the largest of which measured M4.5 quake at 8:50 p.m. The strongest jolt struck about 24 hours later and measured M4.7. The swarm reduced significantly after June 17 but totaled 210 events at month's end.
Other regions of activity included an area near Hebgen Lake, along the west margin of the Yellowstone caldera, and at the Pitchstone Plateau where a M4.2 temblor struck on June 28. It apparently passed without attention.
Special Note: The Utah Geological Survey has an excellent suite of geologic publications, including the "Homebuyers guide to earthquake hazards in Utah". For more info, call: 801-537-3320.
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