Talking quakes, tsunamis: A look at what La Jollans should think about
Map from Scripps Institution of Oceanography's Broadband Seismic Data site shows the Rose Canyon fault. Courtesy: SIO/UCSD
By Dave Schwab
Staff Writer
Local experts say an earthquake and tsunami of the same magnitude as the one that ravaged Japan recently couldn’t happen here.
But they were quick to add that doesn’t mean there isn’t cause to be concerned — or prepared — for a quake, particularly with San Onofre nuclear facility nearby, or a tsunami that might be generated.
“We know there’s going to be another earthquake,” said Debi Kilb, Ph.D., a seismologist with Scripps Institution of Oceanography. “What we don’t know is whether it’s going to be today, tomorrow or a hundred years from now.”
Statistics show every year approximately 500 earthquakes occur in California large enough to be felt. San Diego County, compared to other Southern California areas, has sparse seismicity. However, since 1984, earthquake activity in San Diego County reportedly has doubled over that of the preceding 50 years.
And while the fault nearest La Jolla is the Rose Canyon Fault, it’s the least worrisome to Kilb who sees greater risks from the San Jacinto Fault that runs through Anza, east of Temecula, and the San Andreas, which runs from Point Arena to the Salton Sea.
As scientists like Kilb and Pat Abbott, emeritus professor of geology at San Diego State University, look at the quakes from their vantage points as to the whys and hows, city and county officials have to deal with what happens “when.”
In La Jolla, which has a fault running right through it, residents should be particularly attentive to potential evacuation routes, they said.
An evacuation plan is in place for all areas of the city in the event of an earthquake, tsunami or other natural disaster, said Donna Faller, program manager for the city’s Office of Homeland Security.
“It has all the major ingress and egress routes for all the quadrants of the city,” she said, adding, “You can’t predetermine exact routes. But you can preidentify possible locations where you want people to stage.”
Assistant Police Chief Boyd Long, who used to head the Northern Division which would be in charge of evacuating La Jolla during an emergency, discussed why people need to be educated about where to go during a crisis.
“Access points (south on La Jolla Boulevard to PB, north onto La Jolla Parkway and Genessee Avenue to I-5 and east over Soledad Mountain Road to PB) are limited,” he said. “For a failsafe, I would encourage people to make sure they know each of those exit points out of La Jolla: Don’t rely on any one of them.”
In La Jolla, it appears there has been no particular effort to coordinate a community-level evacuation plan beyond the city’s.
Geologist Abbott, who is the go-to source for San Diego media when a quake gets our attention, said places like Japan have the most severe quakes because they’re on the tectonic plate boundaries where the ocean floor is being pulled beneath the continents. That, he said, results in a “buildup of a huge amount of energy buckling the seafloor, causing huge earthquakes with energy being shoved into the water that generates the tsunami.”
Kilb added more detail about the difference: “Our primary faults (San Andreas, San Jacinto and Elsinore) run parallel to one another northwest to southeast and are of the strike-slip variety,” she said.
They act like “sliding closet doors moving back and forth,” typically generating less severe quakes when they happen, she added.
Another reason for the smaller magnitude quakes here is that they are “relatively shallow, she said, noting that while our faults are similar in length to those in Japan ours our at about 30 kilometers, compared to Japan where the faults like 300 kilometers deep.
That also helps explain why a tsunami like the one in Japan is less likely in Southern California, she added. “A tsunami requires three elements: a big quake, a shallow quake and a large body of water. We only have two of the three — we’re missing the large body of water in relation to most of our faults, which are farther east.”
Even so, she said, a large quake along the San Andreas could trigger an offshore landslide that could displace the ocean water and thus a tsunami.
Abbott outlined the Rose Canyon Fault, which “runs 5 miles offshore of San Onofre nuclear facility, then comes onshore just south of La Jolla Parkway ,then bends and goes down Rose Canyon past the east side of Mission Bay.”
He noted “San Onofre was designed to withstand a 6.5 magnitude quake with a safety factor raising it to 7.0. But it might be prudent to reexamine that engineering to see if there’s any weak spots or vulnerability in the system. It’s not a new facility. Are there any upgrades that are needed?”
Ongoing field and laboratory studies suggest the largest credible earthquake predicted for the coastal and metropolitan areas is a M7.2 on the Rose Canyon Fault and a M7.6 from either the Elsinore Fault or the San Jacinto Fault in the North and East County areas, according to the county’s Office of Emergency Services website.
— Staff writer Kathy Day contributed to this report.
To see data on recent area quakes go to
eqinfo.ucsd.edu/tools/southern_california_recent_earthquakes.php. Note the legend on the bottom left allows you to toggle on/off the different main fault traces of the region.
Image shows readings at the time of the Japan earthquake taken from the seismometer at Mount Soledad that is part of the ANZA Seismic Network operated by Frank Vernon from Scripps Institution of Oceanography. Courtesy: SIO/UCSD
Some useful websites for information on emergencies and natural disasters include
• City of San Diego Office of Homeland Security: http://www.sandiego.gov/ohs/
• County of San Diego Office of Emergency Services: http://www.co.san-diego.ca.us/oes/
• American Red Cross: www.redcross.org/.
Related posts:
- NOAA administrator to give Revelle Lecture in La Jolla
- Grant to aid climate studies at SIO, UCSD
- Eckman named to head Sea Grant
- Memorial services set for Peter Niiler, world authority on ocean circulation
- Scripps glaciologist wins Muse Prize
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Posted by Dave Schwab
on Mar 23, 2011. Filed under La Jolla, News.
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