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Earthquakes are part of life in California. If you live in the Golden State for any significant period of time, you are likely to experience several of them.

As part of the Ring of Fire, the most seismically active zone in the world, the ground in California is constantly shifting. People live with the possibility of “The Big One” striking at any time, which is why billions of dollars have been spent over the decades to improve infrastructure and make buildings more earthquake-resistant.

Here are three surprising facts about California earthquakes.

1. California was hit with a possible 9.0-magnitude quake

There were obviously no seismographs or recordings of any sort in 1700. However, on the evening of Jan. 26, 1700, Northern California and the entire Pacific Northwest were hit with one of the strongest earthquakes in history – believed to be around magnitude 9.0.

How do we know this? Japan has been tracking tsunamis at least as far back as 684 CE and the quake that hit Northern California, known as the Cascadia earthquake, triggered a tsunami that flooded villages in Japan and also caused extensive damage along the Pacific coast of North America.

“We can work backward from the time the tsunami arrived in Japan to determine when the earthquake happened,” the U.S. Geological Survey explains.

The precise epicenter of the Cascadia quake is unknown. The USGS believes it occurred offshore somewhere between Cape Mendocino and Canada.

San Francisco Fire And Earthquake
Ruins of the city after earthquake and fire of 1906, San Francisco, California. (Photo by Hulton Archive/Getty Images)

2. The ground is constantly shaking

The USGS records roughly 10,000 earthquakes in Southern California each year or around 27 per day.

Most of them are so small that they go unnoticed. Only several hundred quakes register a magnitude of 3.0 or greater, and only 15 to 20 of them reach 4.0 magnitude.

California typically sees two to three earthquakes strong enough to cause moderate damage each year, according to the state’s Department of Conservation.

3. The San Andreas fault is not a single fault

No discussion of earthquakes in California is complete without addressing the San Andreas fault. But even that term is a bit of a misnomer.

According to the USGS, the San Andreas fault is not a single fault, but rather an 800-mile-long “fault zone” comprised of many segments.

The average rate of movement along the San Andreas fault zone over the past 3 million years is around 2 inches per year, which is about the same rate that your fingernails grow, experts say.

“Assuming this rate continues, scientists project that Los Angeles and San Francisco will be adjacent to one another in approximately 15 million years,” USGS says.

Editor’s note: This story was updated to clarify some details about faults and earthquakes.