The 4.5 earthquake that occurred near Westley shortly after 9 p.m. on Monday was bigger than any in Stanislaus County going back a century in U.S. Geological Survey records, said USGS research geologist Austin Elliott.
While earthquakes like this don’t necessarily signal anything big is imminent, they are a reminder that the ground can shake at any moment, Elliott noted.
“No individual small earthquake inherently indicates anything larger is coming, and most earthquakes of this magnitude pass without further events and without further larger events,” Elliott said.
Aftershock sequences can last weeks and months, but for an earthquake of 4.5 magnitude, the aftershocks will likely be small and people will stop being able to feel them after a few days, he said.
Stanislaus County is seismically active, but 14 earthquakes in 24 hours is not typical.
“A lot of the people who felt these ones are living in the Central Valley, Turlock, Modesto, Patterson … (and are) probably not so used to having an earthquake occur so close to them,” Elliott said.
The earthquakes Monday were caused by a mix of compressional convergent faulting, where there’s two sides of a tectonic plate coming together, and strike slip faulting, where there two sides sliding past each other, Elliott said.
Elliott said there are known faults in the region, but the earthquakes were too small to pin on a specific fault.
The faults in the region are known to produce earthquakes, but they don’t lead to earthquakes as often as the San Andreas and the Calaveras faults, Elliott said.
He said the earthquakes could have been caused by fault structures that are not mapped.
“Earthquakes of this magnitude — twos and threes and fours — that may be happening, there are all kinds of little fractures and faults that are possible to produce small earthquakes,” Elliott said.
To the west of Stanislaus County are strike-slip faults including San Andreas and Calaveras, and to the east of the county are convergent faults on the margin of the Central Valley.
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Elaine Hadley is a dedicated journalist covering the ever-evolving landscape of U.S. news. With a keen interest in politics and a commitment to uncovering the truth, she provides insightful commentary and in-depth analysis on domestic issues. When not reporting, Elaine enjoys exploring the diverse cultures and landscapes of the United States.
