"If people felt it, it probably would just been a very slight bump under their feet," California State Geologist John Parrish said. "Magnitudes three and less are seldom felt unless one is actually right on top of them."
Two earthquakes struck 5.5 miles north of Truckee, and a large cluster of 33 earthquakes struck 12 miles north of Truckee. The largest earthquake was a magnitude 3.9 that occurred on Monday at around 2 a.m., according to U.S. Geological Survey. The most recent quake struck at 9:17 a.m. and was a magnitude 2.9.
The state's top geologist said this kind of swarm happens in Northern California two to three times every year.
"This looks like a rather common swarm," he said. "That doesn't mean that something larger will not happen, but we have no way to predict those, so we tend to watch them closely and keep monitoring them."
While this was a relatively common occurrence, the California Geological Survey is more concerned about the Hayward fault in the Bay Area.
"We have a forecast that there will be a 99.9 percent chance that California will have a Northridge-style earthquake in the next 30 years," Parrish said. "Northridge-style is a magnitude 6.7 or larger."
They estimate an 85 percent chance of that kind of earthquake happening in Northern California, which could cause up to $200 billion in damage.
"It would simply tear up every building that you've got here on the east shore," he said. "Because you've got old structures, very densely packed together, and you could get a major, major earthquake."
One way the state hopes to mitigate impacts of a major earthquake is an early earthquake warning system, which could be operational in two years.
"If we have an earthquake, we will send out a warning to people before they feel the shaking – that an earthquake has occurred and they have a few seconds to do something," Parrish said. "To take cover or to shut down equipment or to do something along those lines."
The system could help save thousands of lives in a state known for earthquakes.
"We have the largest population, 40 million people, on the shakiest ground in the United States," he said. "And so It's very important for us to maintain these types of programs so that we can provide the public with information on the seismicity in the state."
Even with that system, Parrish expects that it could take up to three days to get outside help in the event of a major earthquake. He recommends having at least three days of supplies ready just in case.
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