Hundreds of low-level and medium-sized earthquakes have struck central Idaho since last month, puzzling geologists who wonder whether the ruptures portend a much larger temblor to come or are merely the rumblings of a seismic fault previously thought to be dormant. The recent earthquake swarm, beginning on March 24 and climaxed by a 4.9 magnitude tremor on Saturday, has produced no reports of injuries or severe damage but has rattled nerves in a region where Idaho’s most powerful known quake, measured at 6.9, killed two children in 1983. Saturday’s earthquake was the strongest recorded in the state since 2005 and was followed on Monday by a magnitude 4.4 event that struck 10 miles north of the small ranching community of Challis, Idaho, according to the U.S. Geological Survey.
The Challis tremor knocked pictures and animal mounts from walls, rattled dishes off tables and was felt by residents in neighboring Montana more than 100 miles from the quake’s epicenter, officials said. The latest seismic surge, including 100 small to moderate quakes on Monday alone, has galvanized government scientists, who planned to install special seismometers in the area as early as Tuesday to more closely track the activity. The likelihood of a severe earthquake coming on the heels of the recent swarm is low, but much is perplexing about the series of tremors, said Bill Phillips, a geologist with the Idaho Geological Survey at the University of Idaho. Such earthquake swarms typically are associated with the movement of molten rock below ground, which geologists credited for the recent quake cluster at Yellowstone National Park, or they are linked to an active fault, he said on Tuesday. More