Earthquakes in Nevada, California? USGS false alert explained.

The US Geological Survey said on X's website that it was “looking into why the alerts were issued.”

Researchers at the University of California are testing a 10-story building using an earthquake simulator

Researchers at UC San Diego simulated a 6.9 magnitude earthquake to see if this 10-story building would maintain its integrity.

A shaking alert was issued via the USGS Early Warning System on December 4, warning that a 5.9 magnitude earthquake near Carson City in western Nevada could cause severe tremors in the area.

But moments later, the survey announced that the alert, sent to people as far west as San Francisco, was a false alarm.

A message was quickly posted at the top of its website, stating that the ShakeAlert Earthquake Early Alarm system had incorrectly alerted of an earthquake near Carson City, Nevada, at 8:09 a.m. local time.

The word “earthquake” was removed from the agency's map and the correction was posted across USGS social media channels. “The event did not occur and has been removed from USGS websites and data feeds. USGS is working to understand the cause of the false alert,” the letter said.

“There was no M5.9 earthquake near Carson City, Nevada this morning,” the USGS told USA TODAY in an email. “We are currently looking into why the warning was issued. We will provide more information as we learn more.”

The agency said that among the questions the USGS and its partners are trying to answer is why the warning was issued “to a wide area of ​​California, including the Bay Area, the Eastern Sierra, and parts of south-central California.”

Although false alerts from the system are rare, earthquakes are not rare in Nevada. It is the third most seismically active state in the country, after California and Alaska.

Keren Bogolob, a seismologist at the Reno Seismological Laboratory at the University of Nevada, confirmed the false alarm.

“This was a false earthquake warning sent by the USGS ShakeAlert system,” Bogolob told the Reno Gazette-Journal, a member of the USA TODAY Network. “We are awaiting more information from the USGS.”

Was that just an earthquake? Here's how to know what's really turning you on

What is the ShakeAlert EEW System?

The USGS Early Warning System is used throughout California, Oregon and Washington to send out alerts when strong shaking is expected immediately. The USGS monitors and reports earthquakes and assesses impacts and risks, and is part of a larger National Earthquake Hazard Reduction Program, a four-agency partnership created by Congress.

“The ShakeAlert system accurately detected the majority of earthquakes that have occurred within the area of ​​operations since the completion of the public offering,” the survey concluded in an August 2024 review.

The review evaluated the warning system's performance during 95 earthquakes of magnitude 4.5 or higher alerted by the system between October 2019 and August 2023. Although the system concluded that seven of those quakes were false, they were in fact real quakes, the USGS review found.

The USGS report said that only one of the 95 events was not an actual earthquake. The review found problems with reporting earthquakes that were along the edges of the seismic grid, which runs along the California-Nevada state line.

The city of Dayton, where the earthquake alert indicated, is about 20 miles east of the state line. USA TODAY has reached out to the USGS for further comment.

Vibration is not uncommon in Nevada

While Thursday's report was a false alarm, Nevada has seen large earthquakes and is full of fault lines.

Since January 1990, seismologists have reported 80 earthquakes of magnitude 4.5 or greater in Nevada, according to a USGS database. Thousands of less powerful earthquakes have been reported in the region.

The largest earthquake since 1990 measured 6.5 on May 15, 2020, with its epicenter in Monte Cristo. A magnitude 6.1 earthquake occurred on September 12, 1994. A magnitude 5.7 earthquake was reported on December 9, 2024, and a magnitude 4.8 earthquake was reported on November 29, 2025.

However, of those 80 events reported since 1990, 10 were actually nuclear explosions captured by seismic monitoring, according to USGS data. All of these cases were reported between June 1990 and February 1992, and all were more than 200 miles south of Carson City.

Real earthquakes occurred elsewhere on December 4th

Nearly three dozen earthquakes were reported worldwide by 2:30 on December 4, including a 5.8 magnitude earthquake near Tomchuk, China, and a 5.5 magnitude earthquake in the Pacific and Antarctic regions. Three 5.3 magnitude earthquakes were reported, one each in the Kermadec Islands area, Fiji and El Morro, Mexico.

See map below for seismic activity detected on December 4.

Reactions to false alarm

At Roadrunner Cafe in Dayton, a regular customer said he heard there was an earthquake over the radio, but that came as a surprise to Shannon Mackey, manager of the family-run breakfast spot. It was breakfast as usual at the café, and McKee said she didn't feel any vibration.

Officials in Leon County, where the false alert said the event was based, sent a notice to its residents. “We are awaiting additional information and will share it when it is available,” the district stated. “There is currently no risk to the public.”

The earthquake warning and retreat quickly attracted widespread attention and theories on social media.

“Needless to say, this has led to widespread speculation on social media about how this could have happened,” Alan Gerard, a retired federal meteorologist, wrote in a Substack blog post on December 4. “We definitely need to understand more about what happened today before jumping to conclusions,” Gerrard wrote.

But he added that such events reinforce “the importance of federal science to the safety and livelihoods of our country's citizens.”

This story has been updated to add new information.

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