It is an unremarkable fault similar to hundreds of others throughout California. It lies in the Los Angeles basin, extending some 25 miles from the Puente Hills region in the southeast to south of Griffith Park. Scientists refer to it as a “thrust fault,” but unlike other fissures of that type, it has no apparent visual features. No cracks. No irregular topography. And it was not regarded by geologists as particularly dangerous.
Few residents of La Habra even knew it was there.
But that did not stop the Puente Hills thrust fault from rupturing in March 2014, shaking homes and rattling nerves one Friday night. The earthquake’s 5.1-magnitude was not overly noteworthy, but because the epicenter was a relatively shallow 3.6 miles in depth, its effects were strongly felt by residents. We estimate that approximately 23,000 of our policyholders alone felt it!
And the damage was significant, too. The temblor and an aftershock inflicted millions in property damages on the region.
As we approach the third anniversary of the La Habra event, let’s reflect on this unremarkable, forgotten fault that lies beneath the feet of some 3.7 million Californians.
There are thousands of known faults crisscrossing our state—and scientists continue to discover new ones. UCERF3 puts the probability of a 6.7M or greater earthquake striking California in the next 30 years at 99.7 percent. The probability of the big one, a 7.0M or greater, is a bit more optimistic: it's only 75 percent or higher.
The risk is real.