Hollister - Hollister residents received a jolt Wednesday afternoon when a mostly harmless 4.0 earthquake struck the county, followed by two smaller quakes.
"Of course, in San Benito County you get so many earthquakes," said Steve Walter, a seismologist with the United States Geological Survey. "But this one was a little unusual."
The quake struck at 1:20pm, with its epicenter located near the intersection of Freitas and Mitchell roads, roughly three miles west of Hollister and five miles east of San Juan Bautista. It was ranked as a 4.0 or "light" earthquake on the Richter scale, with a 1.0 being a microquake and a 10 being a quake of awesome force. The quake originated 1.9 miles below the surface of the earth.
This was followed by a microquake ranking 2.8 at 1:38pm. A third, even smaller microquake may have occurred afterward but was not confirmed by the USGS by press time.
Neither the Hollister Police Department or San Benito County Sheriff's Department received any calls reporting damage.
The quake was unusual for two reasons, Walter said. San Benito County quakes most often originate from the San Andreas Fault area, or the Calaveras Fault. This one took place from a point between the two and cannot be confirmed to have originated from either.
It was the first 4.0 or greater quake to have occurred in the area between the faults since at least 2000, according to the USGS.
Also, most local earthquakes are characterized by horizontal motion, as the earth's plates move past one another. This quake, however, moved in a vertical fashion.
"There were elements of horizontal motion, but most of it was vertical, and that's rare (in the area)," Walter said.
The quake could have been felt as far north as Pleasanton and as far south as Monterey, Walter said. One quake report on the USGS Web site came from San Diego, but Walter said it was highly unlikely.
"Sometimes people hear there was an earthquake and think, 'Oh, that was what I felt,'" he said. "When usually it's just something like a truck going by."
Danielle Smith covers education for the Free Lance. Reach her at 637-5566, ext. 336 or dsmith@freelancenews.com.
Danielle Smith
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