The latest activity began with a strong magnitude-6.7 quake March 16 that caused more than 100,000 people to briefly evacuate low-lying areas. Hundreds of smaller quakes have followed in the weeks since, keeping people on edge as scientists said there was no way to tell if the unusual string of tremors was a harbinger of an impending disaster.
Mark Simons, a professor of geophysics at the California Institute of Technology, says historical records suggest that the region should anticipate an even bigger quake in the future.
"The key point here is that this magnitude-8.2 is not the large earthquake that we were expecting in this area," Simons said. "We're actually still expecting potentially an even larger earthquake.
"We expect about another 8.8, 8.9-magnitude earthquake here sometime in the future. It could be tomorrow, it could be in 50 years. We do not know when it's going to occur."
ABC News' Joshua Hoyos, ABC News Radio and The Associated Press contributed to this report.