"What we know is for the last 700 years, earthquakes on the southern San Andreas fault have been much more frequent than everyone thought," said the study's lead author Sinan Akciz.
"Data presented here contradict previously published reports," he added.
With 37 million people living in southern California, chiefly in the cities of Los Angeles, San Diego and Anaheim, a major earthquake could kill between 2,000 and 50,000 people and cause billions of dollars in damage, scientists said.
UCI seismologist Lisa Grant Ludwig, the study's chief investigator, said people in the area should already be taking precautions.
"There are storm clouds gathered on the horizon. Does that mean it's definitely going to rain? No, but when you have that many clouds, you think, I'm going to take my umbrella with me today. That's what this research does: It gives us a chance to prepare," she said.
For individuals, that means having ample water and other supplies on hand, safeguarding possessions in advance, and establishing family emergency plans.