A “swarm” of more than 600 earthquakes in just 24 hours struck the Mammoth Lake region of California, east of the Sierra Nevada mountains, between Thursday and Friday morning.
According to the Los Angeles Times, at least 109 earthquakes were magnitude 2.0 or greater, while at least six were magnitude 3.0 or greater. However, most of the earthquakes were much smaller in power.
“This is one of the largest earthquake swarms we’ve seen in the past decade or so,” U.S. Geological Survey seismologist David Shelley told the Times. “We’ll be tracking it closely.”
According to Shelley, earthquake swarms in the area known at the Long Valley Caldera are not uncommon. The last such swarm occurred in July, when about 200 earthquakes of magnitude 2.7 or smaller struck the region.
In 1997, thousands of earthquakes, some as powerful as magnitude 4.9, rattled the region for months. In the 1980’s, an earthquake swarm featured magnitude 6.0 tremblors.
Scientists initially thought the earthquake activity could be due to volcanic activity in the region; the Long Valley Caldera is part of a “network” of 17 volcanoes throughout the state of California. The report notes that the last time the Long Valley Caldera erupted was 57,000 years ago.
“We are not having any eruptions in California… in the near future,” Shelley told the Times.
Instead, scientists believe the quakes may have been triggered by increased stress on deep-underground tectonic plates, caused by water pressure from hot springs shifting through the ground surface.
Shelley told the Times the earthquakes could continue.
“At this point, we don’t know if it would continue to die down, or if there’d be another stage to this swarm,” Shelley said. “There is certainly an interesting scientific opportunity to better understand the processes that are driving this activity.”