SAN JOSE, Calif. (KRON) — A 5.1-magnitude earthquake and aftershocks were generated by the Calaveras Fault strike-slip fault line, according to the U.S. Geological Survey.
The earthquake jolted San Jose just before noon Tuesday and its magnitude was the biggest the San Francisco Bay Area has experienced in eight years. The epicenter was on the east side of San Jose at a depth of 6.1 kilometers. The USGS recorded two aftershocks with 2.9 and 3.5 magnitudes.
The Calaveras Fault has been seismically calm this past decade. It’s last notable earthquake happened around this same time of year, October of 2007, when the 5.4-magnitude Alum Rock quake ruptured.
The fault line also generated the magnitude-6.2 Morgan Hill earthquake in 1984, and the magnitude-5.9 Coyote Lake quake in 1979.
The Working Group for California Earthquake Probability assigned an 11% probability that the Calaveras Fault would produce a magnitude 6.7 or larger earthquake in the next 30 years.
One hour after Tuesday’s tremblor, San Jose’s emergency officials said there were no reports of major damages or injuries.
The San Jose Fire Department wrote, “We’re happy to report no emergency calls related to this morning’s quake.” The San Jose Police Department added, “No reports of damage or injuries thus far. We will update you if that changes. Back to regularly scheduled programming for us, combating crime and keeping our community safe.”
Bay Area residents felt widely-different experiences of motion depending on how close they were to the epicenter.
Seismologist Lucy Jones explained, “The Earth produces energy. (A quake) begins at the epicenter. The waves travel from the fault. If you are nearby, you feel all of that energy and it’s a very sharp motion. As the waves travel, the high frequencies die off more quickly than the low frequencies. Long period energy travels farther. So when you are far away in San Francisco, only that long period motion is left.”
Cal OES reported that 100,000 residents received advance notifications before shaking started through the state’s earthquake early warning system. Advance notice varied from two seconds for those very near the epicenter in San Jose, to 18 seconds for people in San Francisco.