On Sunday morning, 30 March, a magnitude-4.8 quake struck Yellowstone National Park, centered about 6.4 kilometers northeast of the park’s iconic Norris Geyser Basin. That temblor, the largest to strike the park since 1980, is part of a series of at least 25 quakes that began in the area on Thursday, 27 March. Besides the main shock, the largest quake in this group measured magnitude 3.3.
Is such seismic activity normal?
Yes. There have been three clusters, or swarms, of earthquakes beneath Yellowstone in the past 6 months, says Robert Smith, a geophysicist at the University of Utah in Salt Lake City. Sunday’s quake is notable only because it’s somewhat larger than recent temblors. On average, the park experiences about 3000 quakes per year, he notes: “Yellowstone never stops shaking.”
What caused the quakes?
In general, the presence and movement of molten material at shallow and intermediate depths beneath Yellowstone is what triggers much of the seismic activity there. (The heat from that molten rock, of course, is the driving force for the park’s iconic geysers.) Sunday’s magnitude-4.8 quake was centered in a region where instruments have measured the landscape rising and falling for the past several months. That connection, too, is normal: A previous period of uplift in the same area between 1996 and 2003 was also accompanied by increased seismic activity. Nevertheless, Smith says, the causes of specific quakes and swarms are difficult to pin down. There have been spates of quakes without uplift, and there have been extended periods of uplift without abnormally high seismic activity.
Are these quakes related to those in southern California?
Probably not. Although it’s possible for a quake in one area to trigger others along faults in a distant region, the Yellowstone quakes are much more likely to be related to geological changes taking place locally within Earth’s crust.
Do the Yellowstone quakes pose a future threat?
Unlikely. There’s no sign that the current swarm of quakes is any different from those experienced there in recent months or years, and it doesn’t seem to be linked to any volcanic processes, he notes.
A field team from the U.S. Geological Survey arrived in Yellowstone on Sunday. They’re assessing the area near the quake’s epicenter to see if the event altered the terrain, and they’ll also check to see if the seismic activity has changed the size or eruption frequency of geysers in the area.