Raymond “Ray” Gaines is a Los Angeles Fire Department Air Rescue pilot in the midst of a divorce from Emma and planning a trip to San Francisco with his daughter Blake. Meanwhile, Caltech seismologist Dr. Lawrence Hayes and his colleague Dr. Kim Park are at Hoover Dam doing research for a new earthquake predicting model when a nearby and previously unknown fault ruptures. This triggers a 7.1 magnitude earthquake that collapses the dam and kills Park after he rescues a little girl and throws her to Hayes as he falls to the collapsing ground. When Ray is called into work because of this, Blake goes with her mother’s new boyfriend Daniel Riddick to San Francisco, instead of Ray.
Hayes discovers that the San Andreas Fault is shifting and will soon cause a major earthquake, thereby destroying cities along the fault line. Emma is having lunch at a hotel in Downtown LA with Daniel’s sister Susan when the fault shifts triggering a 9.1 magnitude earthquake, with Susan among the casualties during the event. Rather than reporting for emergency rescue duty, Ray saves Emma from the collapsing building, and they escape the city aboard his helicopter, barely managing to swerve around the US Bank Tower as it comes crumbling down.
In San Francisco, Daniel brings Blake to his office where she meets Ben, an engineer from England seeking employment and his brother, Ollie. Daniel and Blake leave the premises, but they become trapped in their car in the parking garage after a string of earthquakes. Daniel flees but Blake is found by Ben and Ollie, who help her escape. They then find a working phone in Chinatown and Blake calls Ray and Emma, who fly to San Francisco to save her.
In route, Ray’s helicopter fails, forcing him to make an emergency landing at a shopping mall in Bakersfield. Amid the chaos of looting, he steals a truck and he and Emma escape. They come across an older couple broken down on the side of the road where the San Andreas Fault has opened up, blocking the road and the couple, who happen to own an airplane, agree to give it up in exchange for Ray’s vehicle.
In San Francisco, Blake, Ben and Ollie are trying to find a place to signal Ray, as the point they agreed to meet at, Coit Tower, is engulfed in flames. On approach, Ray and Emma are forced to parachute in the city when a 9.6 magnitude quake hits the city, becoming the largest earthquake in history. Much of the city is left in ruins and Blake, Ben and Ollie narrowly survive. Ray and Emma, realizing they cannot make their way through the destroyed city, are able to commandeer a boat only to see that the water in the bay is beginning to recede, indicating that a megatsunami is approaching.