JACKSON HOLE, Wyo. — The U.S. Geological Survey says a magnitude-4.8 earthquake that shook northern Yellowstone National Park on Sunday is the strongest there since 1980.
But the quake was still considered relatively light, and its location didn't raise concerns about the park's supervolcano, which experts say has the potential to erupt with a force about 2,000 times the size of Mount St. Helens, potentially having worldwide effects.
The University of Utah Seismograph Stations says the earthquake occurred at 6:34 a.m. about 4 miles north-northeast of the Norris Geyser Basin. The Montana border towns of West Yellowstone and Gardiner felt the quake.
Meanwhile two earthquakes in California on Friday put residents and experts there on edge. It has been 20 years since Southern California experienced a major earthquake, a powerful 6.7-magnitude temblor that rolled through Northridge, killing 57 people. This stretch of seismic calm, though welcome in obvious ways, has undermined efforts to force Los Angeles to deal with what officials describe as potentially lethal deficiencies in earthquake preparation.
Since the Friday evening quakes — a relatively small one with a magnitude of 3.6, followed by a long and rolling 5.1 quake — Los Angeles has been shaken by nearly 175 smaller aftershocks. It is the first time since 1997 that the area has suffered an earthquake with a magnitude greater than 5, and it comes two weeks after a 4.4 earthquake jolted residents awake.
None of these quakes caused injuries or widespread damage, other than broken water pipes and some homes that have been declared at least temporarily uninhabitable. But geologists see them as the predictable end of a cycle: a return to what might be an uncomfortable normal in which 5-magnitude earthquakes become routine events.
"The last 17 years has been the quietest time we have ever seen," said Lucile M. Jones, a seismologist at the U.S. Geological Survey. "Maybe we're starting to turn back to more normal levels."