Earthquakes remain one of the top concerns for millions of Californians. While the San Andreas Fault dominates the public imagination, a leading expert says the state’s seismic risk is far more widespread and complex.
Seismologist Lucy Jones says that the seismic risk in the state is not limited to the San Andreas Fault. In Southern California alone, there are hundreds of faults.
Learning from Past Earthquakes
The good news is that our understanding of these hidden dangers has grown considerably in recent decades. While no major “new” faults have been discovered, advanced technology now allows scientists to map subsurface structures buried kilometers deep.
“The Whittier Narrows earthquake and then the Northridge earthquake both happened on faults that didn’t come all the way to the surface and therefore were not recognized until the earthquake happened,” Jones said. “Because of those earthquakes, we then went and did other studies, and we basically ran CAT scans of the Los Angeles basin to map out the picture of those faults, so I think we have a pretty good handle on where they are.”
Weaker Faults Could Be More Dangerous
Jones warns that the next major threat may not come from the most famous fault. In fact, she suggests that so-called “weaker” faults could potentially generate larger earthquakes in the coming decade.
“The weaker faults have bigger earthquakes because the size of the earthquake is the length of the fault it moves, and if it’s strong and lots of heterogeneities, the little earthquake begins and can’t keep on rupturing down the fault and gets stopped, so you get lots of these little earthquakes instead,” Jones said.
Understanding fault “activity” requires a geological perspective, Jones added. Movement on an active fault might be as slow as millimeters per year.
“An active fault, right, geologic time, the slip accumulates on the fault literally in millimeters per year. The fastest of the San Andreas is 35 mm a year, which is about an inch and a half,” Jones said. “It’s like the way your fingernails grow, but imagine if you didn’t cut your fingernails for 200 years.”
GPS Stations
Since the Northridge quake, a permanent network of GPS stations has been deployed, precisely measuring the gradual strain accumulation across tectonic plates. This data underscores the reality: everyone in the region lives within about five miles of an active fault.
“All of us live within probably 5 miles of an active fault and which one is going to go in your lifetime is a random subset of that,” Jones said.
Community Aid & Ties
When it comes to surviving and recovering from the inevitable major quake, Jones emphatically shifts the focus from stocking supplies to strengthening social ties.
“When people ask me about earthquake preparedness, I refuse to talk about kits. I say forget the kit, talk to your neighbor,” Jones said. “Look at what’s happened in Altadena in the last year and that’s a community that’s come together and they are recovering well because they turned to each other, so it gives me a lot of hope that we will do well with the next earthquake we can if we can learn from Altadena about how to work together.”
Source: CBS News
