Californians have heard about “The Big One” for decades. The term refers to a potentially catastrophic earthquake that will strike one of the state’s major fault systems, particularly the San Andreas Fault and San Jacinto Fault. While scientists agree that another major earthquake will occur one day, they stress that they cannot predict the exact date, time or location.
Recent studies and seismic observations have renewed concerns about earthquake risks in California, especially as tension continues to build along several active fault lines. Here’s what experts know about the potential next “big” state.
When was the last “big” earthquake in California?
It depends on how you define “the big one.” For Southern California, experts point to the 1994 Northridge earthquake, which had a magnitude of 6.7, killing 57 people and causing an estimated $20 billion in damage. Although it was devastating, Northridge was smaller than the catastrophic seismic scenarios often associated with the “big quake.”
Others consider the last true “big earthquake” to be the 1906 San Francisco earthquake. The quake had a magnitude of 7.9 and ruptured a large portion of the San Andreas Fault. The earthquake and fires destroyed parts of San Francisco and killed thousands of people.
The other recorded “big storm” occurred in 1857, and had a magnitude of 7.9. It has torn the southern portion of the San Andreas Fault, between Barfield and Wrightwood, California.
Scientists are concerned about the southern part of the San Andreas Fault to this day.
When will the next big earthquake happen?
As for the next big event, the short answer is that no one knows when it will happen, but it is imminent.
According to the United States Geological Survey (USGS), earthquakes cannot currently be predicted with sufficient accuracy to determine the exact date, time, or location of when or where the next major earthquake will occur.
However, researchers have developed models that estimate the likelihood of large-scale earthquakes in California. Previous USGS forecasts found high potential for earthquakes of magnitude 6.7 or higher within the next few years or decades.
But as of 2026, a recent study found that parts of the San Andreas and San Jacinto fault systems in Southern California are currently experiencing some of the highest levels of stress. One major area of concern is Cajon Pass between the San Gabriel and San Bernardino Mountains.
Unfortunately, as mentioned earlier, scientists can assess potential earthquake risks, but they cannot predict the exact timing. So the next “big event” could happen tomorrow.
What is the highest magnitude of an earthquake?
There is no theoretical upper limit on the magnitude scale for measuring earthquakes. The largest earthquake ever recorded was the 1960 Valdivia earthquake in Chile, which had a magnitude of 9.5.
By comparison, the quake commonly called the “Great California Earthquake” would likely have a magnitude of 7.8 to 8.3, depending on which fault bursts and how much it breaks.
What will happen when California experiences the next big earthquake?
Scientists expect widespread shaking and infrastructure damage when a major earthquake occurs in San Andreas.
One of the most widely cited USGS scenarios, known as the ShakeOut Scenario, depicts a hypothetical magnitude 7.8 earthquake on the southern San Andreas Fault. Severe tremors are expected across Southern California, from Los Angeles to San Bernardino counties, and about 1,800 deaths and $200 billion in damage are estimated.
Experts are urging residents to prepare emergency kits and contingency plans before the next major earthquake strikes.
