Earthquake initially centered in Farmington was ‘phantom’ but felt real to residents

The initial report centering Thursday afternoon’s earthquake in Farmington may have been a “phantom” but it sure felt real to residents of the south San Joaquin County town.

The actual earthquake struck at 3:49 p.m., registering magnitude 6.0, and was centered in the Little Antelope Valley about four miles south of Coleville in Mono County. The United States Geological Center originally reported a second earthquake of 4.8 magnitude in Farmington, about 150 miles away.

But that second quake was later removed, and the USGS explained it has to do with automated reporting.

“There is a trade off between the speed of our earthquake notifications and number of false alarms in the same way that any kind of ‘breaking news’ story may have substantial changes or corrections as more information is received.,” The USGS says on its website. “The faster we release earthquake locations and magnitudes, the more likely it is that the information may be erroneous.”

Jackie Caplan-Auerbach, a seismologist at Western Washington University, explained it this way in a series of Twitter posts:

“Location algorithms can sometimes yield an incorrect location, though. This is because they are somewhat tuned to what they expect to record. For example, a seismic network in California is focused on recording CA quakes, so the algorithm starts with that assumption.

“...Luckily, humans are smarter than computers, and we always have humans review the algorithm’s output. Sometimes...and this is actually pretty rare...we find a phantom quake and delete it from the record.”

Jim Murray of Escalon was at a gas station in Farmington to return a friend’s truck after doing some work on it. He said when the earthquake started, he thought his friend was playing a joke and trying to move the truck while he was inside it.

In the 20 years he’s lived in the area, Murray said this one is the biggest he’s felt.

“That was pretty big,” Murray said. “It literally felt like someone was grabbing the back of the truck and just shaking it.”

This story was originally published July 8, 2021 at 5:57 PM with the headline "Earthquake initially centered in Farmington was ‘phantom’ but felt real to residents."

Lydia Gerike

The Modesto Bee

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Lydia Gerike began covering breaking news for the Modesto Bee in February 2021. She graduated from Indiana University with degrees in journalism and international studies. Lydia has previously reported as a fellow or intern at the Indianapolis Star, Hartford Courant and Oregonian.