A 4.2 magnitude earthquake was detected near Isleton Wednesday, according to the U.S. Geological Survey, triggering a ShakeAlert for many in the Sacramento region.
The earthquake hit around 9:29 a.m., about 35 miles southeast of Sacramento near the Sacramento-San Joaquin River Delta. While more reports of shaking were registered in the Bay Area, people in the Central Valley from Roseville to Modesto also felt the quake.
Currently, there are no reports of damages or injuries.
Lori Nezhura, the deputy director of planning, preparedness, and prevention at the California Governor’s Office of Emergency Services, said impacts from earthquakes are typically felt when they hit magnitudes of 5.4 or above.
However, she added that the shaking from an earthquake might feel more intense at lower levels if it occurs “under an urban center or in an area where there’s a lot of soft soil or a landfill.”
“The shaking would be much more intense,” she said. “So even a 4.1 or two might jolt you.”
She said this may be why Bay Area residents felt the earthquake, while residents further east near Sacramento may not have.
“For instance, to the east, which is where I live, I did receive the alert, but I didn't feel any shaking,” Nezhura said. “But then again, I live in the foothills where we're on solid bedrock.”
Nezhura said California sees thousands of low-level earthquakes annually. However, the magnitude of those quakes typically lies at 3.0 or below. Earthquakes in the range of 4.1 to 4.5 are less common.
“We do receive less than a handful — maybe two to five a year — and we’ve already had two,” Nezhura said, referring to the 4.8-magnitude earthquake in Humboldt County earlier this week.
She said the Humboldt-area earthquake was an aftershock from last year’s 6.4-magnitude earthquake near Ferndale. This 4.1-magnitude earthquake, however, is not linked to another and occurred on a “known fault line.”
“It's not unusual,” she said. “In fact, when we see these lower level earthquakes in the 4.0 range, it's actually good that these faults are releasing pressure at this lower level versus storing it up and having a large rupture.”
The quake comes one day after the 34th anniversary of the Loma Prieta earthquake, the 6.9 magnitude event that killed 63 people and caused more than $6 billion in damage in the Bay Area.
Sacramento residents will get another earthquake alert tomorrow as part of the Great California Shakeout, a yearly test of the state's earthquake preparedness.
Correction: A previous version of this story incorrectly stated the magnitude of the Loma Prieta earthquake. It was 6.9.
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