A pronounced tremor caught the attention of residents from the Bay Area to the Great Basin on Thursday afternoon, local time. No injuries or serious damage were immediately reported.
The rumbling stemmed from a preliminary magnitude 6.0 earthquake, first noted as a 5.9 magnitude, near the California-Nevada border at 3:49 p.m., roughly 20 miles southeast of Markleeville, California, according to the U.S. Geological Survey. It had a depth of roughly 4.6 miles. Within the following two hours, more than 30 aftershocks followed, along with what one expert called a "phantom quake."
People who were quick to check the USGS website might have caught a glimpse of a preliminary report of a magnitude 4.8 earthquake near Stockton, California, that quickly followed the magnitude 6.0 quake, only for the former to disappear moments later.
"The Stockton 'earthquake' was probably the result of incorrect association of some of the waves from the Nevada quake with a secondary source," Jascha Polet, professor of geophysics at Cal Poly Pomona, said over Twitter.
In an earlier post, she alluded to the event as a possible "phantom quake," or non-existent quake.
A preliminary 6.0 earthquake was reported near the California/Nevada border on Thursday evening. (photo/USGS)
"Automatic systems that locate quakes sometimes get confused, especially if there are very nearby few stations," seismologist Dr. Lucy Jones explained over Twitter. "The web pages get updated when those mistakes are corrected. If you look now, you will see there is no earthquake near Stockton, only the [M6] south of Lake Tahoe."
While the magnitude 4.8 was something of an error, the magnitude 6 and its aftershocks were very real -- and they were felt by people from the Bay Area to the Great Basin.
Social media users from the Bay Area to Reno, Nevada, shared they had felt the shaking, including a few National Weather Service offices.
Automatic systems that locate quakes sometimes get confused, especially if there are very nearby few stations. The webpages get updated when those mistakes are corrected. If you look now, you will see there is no earthquake near Stockton, only the M5.9 south of Lake Tahoe. pic.twitter.com/LJRr0Suynn
— Dr. Lucy Jones (@DrLucyJones) July 9, 2021
Rockslides closed about 40 miles of U.S. 395, a major route through the northern Sierra Nevada, The Associated Press reported. A few cars were struck, but nobody was injured, according to the California Highway Patrol. While portions of the interstate were later reopened, crews remained at the scene in case of aftershocks.
"The earthquake rupture occurred along the eastern edge of the Sierra Nevada, which is known to have multiple active faults," AccuWeather Senior Meteorologist Jim Andrews explained. "The fault mechanism indicates "normal" faulting along a north-south axis. This is consistent with known spreading of the crust beneath the western margin of the Great Basin."
Graham Kent, director of the University of Nevada, Reno's seismological lab, told the AP that regionally, "this would be the largest one in almost two and a half decades."
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