by In the last few days, there has been one earthquake after another in Southern California. A 3.6 in Ojai on May 31st. Two of similar size under the East Los Angeles area of El Sereno. Three more quakes near Newport Beach and Costa Mesa.
Although these tremors were much weaker than historical tremors such as the 6.7 Northridge Earthquake in 1994, which caused an estimated $20bn in damage and killed over 57 people, do they indicate that the Big One, as it is called, in a state sitting on multiple, very active faults?
The famous San Andreas is 800 miles long, stretching from near the Mexican border, east past Los Angeles, then up the coast north of Sacramento.
Major earthquakes along the fault occur every 180 years or so, and the San Andreas hasn’t had a powerful one since 1906. The US Geological Survey estimates it has a 60 percent chance of producing a magnitude 6.7 or greater in the Los Angeles area. in the next 30 years.
Of even greater concern is the Cascadia Subduction Zone, which stretches from Northern California to British Columbia, Canada. It’s overdue for an even bigger shakeup compared to historical averages.
So, are the recent earthquakes a harbinger of something bigger, or just business as usual in a state that experiences about 35 tremors a day?
The El Sereno earthquakes, for example, occurred directly under the Puente Hills thrust fault, which runs under central Los Angeles and Orange County. The 10-mile deep fault angles like a ramp and is closest to the surface near the LA campus of the University of Southern California. If an earthquake along this fault strikes the loose ground of the Los Angeles Basin, it could increase the intensity of an earthquake by up to ten times compared to areas located on bedrock.
Meanwhile the Newport Beach-Costa Mesa temblors occurred, near the Compton thrust fault, which could raise up to 5 feet on the LA River in a strong tremor, wreaking great on city sewage systems. According to geologists there have been six earthquakes above magnitude 7 along the fault in the last 12,000 years.
The scientists argue that rather than focusing entirely on the largest quakes in terms of size, the main question is how much damage they could do to closely spaced areas. The San Andreas, despite its famous reputation, runs for large parts through a desert with a population of spares.
“In some ways, the ‘big one’ in terms of damages and deaths would be ones that would run through town rather than one that is far away,” said Dr. Pat Abbott, professor of geology emeritus at San Diego State University, with KSWB. year. “There’s the magnitude of the earthquake, and then there’s also where you’re located relative to where the fault is moving.”
He cited large earthquakes such as the San Andreas earthquakes of 1857 and 1906, as well as the Northridge earthquake of 1994, which were all below the magnitude 8.0 considered in “Big One” cases but still caused “terrible” damage.
“Unfortunately, earthquake prediction remains an extremely challenging endeavor,” according to the California Governor’s Office of Emergency Services website. “Although scientists can monitor fault lines and detect patterns of seismic activity, they cannot reliably predict earthquakes.”
Instead, scientists deal more in the realm of long-term probabilities, which can inform what high-risk areas can do to prepare for the day when the hard-to-predict prospect of a major quake arrives. .
For example, the USGS estimates that there is a 72 percent chance that an earthquake of magnitude 6.7 or greater will hit the San Francisco Bay Area in the next 30 years.
Achieving a higher level of accurate prediction is the “holy grail” of earthquake science, University of Washington seismologist Harold Tobin wrote last year.
“Science has not yet found a way to make actionable earthquake predictions,” he wrote. “A useful prediction would specify time, place and amount – all of which would have to be fairly specific, with enough advance notice to be worthwhile.”
In the meantime, until that magical predictor code is unlocked, governments can push preparedness measures like digital warning systems, practice drills, and construction retrofits, while individual citizens are advised to have emergency kits and get down on their knees , to cover their heads. and neck, and hold on to something stable when shaking starts.
