The moderate earthquake that struck Southern California in spring did more damage than people may think – and a bigger quake on that fault could be more devastating than a “big one” on the region’s infamous San Andreas Fault, a newly released report shows.
Karen Clark & Co. issued a new report on the La Habra earthquake. The report examines at the impact of the March 28 quake, the geography of Greater Los Angeles, and possible future earthquake scenarios for the area.
“It wasn’t on a lot of companies’ radar because it was so small,” Clark said of the magnitude 5.1 temblor.
But it caused significant, low-level damage throughout the region, proving “even this very small earthquake in California did cause damage,” Clark said.
“This earthquake caused, in total losses, more on the order of $100 million,” she said.
The report shows damage to homes included: toppled chimneys and unreinforced masonry fences; plate glass damage; contents damage; cracks in walls.
A month after the quake the California Earthquake Authority reported it had paid numerous claims for damage to homes that sustained “relatively minor damage,” and the quake shook up people’s interest in earthquake insurance sending droves of visitors to CEA’s website the day after the shake.
Policy sales jumped following the La Habra earthquake by nearly as much as the spike in policy sales following the March 11, 2011, magnitude-9.0 Tohoku earthquake in Japan, CEA reported
According to CEA officials, home insurance companies that offer CEA policies responded to hundreds of calls from California residents asking if they have coverage for earthquake damage.
Looking at the possibility of bigger quakes, scientists and engineers at Karen Clark & Co. conducted analyses on the impacts of magnitude 6.1 and 7.1 earthquakes on the Puente Hills Fault, the nearly 25-mile blind thrust fault that produced the La Habra quake.
They found that an M6.1 event would result in estimated total losses of more than $20 billion, while an M7.1 earthquake would cause over $300 billion in total losses – an M7.1 would rupture the entire length of the fault, impacting an area of over 621 square miles, including downtown Los Angeles, according to the report.
“When people think of the big one in California they think of the San Andreas Fault,” Clark said. “But this Puente Hills Fault system is very significant.”
Fortunately the return period of an M6.8 to M7.1 quake on the fault is longer than 1,000 years. While that’s far and few in between, such a quake is likely to cause more damage and losses than a big quake on San Andreas, according to the report.
One reason is location. The fault is along a highly populated area of Southern California, whereas the San Andreas Fault runs through many rural areas. Puente Hills Fault runs from the suburbs of northern Orange County through the San Gabriel Valley under downtown Los Angeles and terminates in Hollywood, according to the report.
Puente Hills Fault’s surface is relatively horizontal and slopes underneath a large region of the Los Angeles basin. Other faults in the area are almost vertical in orientation, and will likely affect a smaller surface area, according to the report.
“A large earthquake on the Puente Hills Fault could cause intense shaking felt over a much larger area resulting in an even more devastating earthquake than a rupture on the San Andreas Fault,” the report states.
The lesson of the La Habra quake for insurers and scientists is that they need to look more at the lesser-known, and often lurking, potential risks laying beneath their feet.
“The Northridge quake was a surprise, the Landers quake was surprise, and then you look at the Tohoku earthquake in Japan with a 9.0 in a fault system that scientists thought couldn’t produce a 9,” Clark said. “We tend the focus on the research that’s already available rather than looking at what could happen.”