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In the wake of L.A’s temblor, earthquake expert John Dvorak explains the special threats facing San Diego and the dueling theories about whether we’ll ever be able to predict when the ground will shake beneath us.
California is earthquake country, from the San Andreas fault, which marks the edge of a tectonic plate, to the smaller but still dangerous faults that riddle San Diego County. We remember this every once in a while when we’re shaken out of bed, as Los Angelenos were on Monday morning.
Things have been quiet in San Diego lately, however, with the exception of Easter Sunday’s shocker of a quake in 2010. Looking back even further, the entire state had a rather quiet 108 years, with only a few quakes in the range of magnitude 7.
It may not seem like much of a lull to those whose loved ones died when quakes hit the Bay Area, the San Fernando Valley and Northridge from the 1970s through the 1990s.
But quakes are indeed taking some time off, says John Dvorak, author of the new book “Earthquake Storms: The Fascinating History and Volatile Future of the San Andreas Fault.” He says the last century was much quieter than the previous 100 years.
That, he says, can’t last. Dvorak, a geophysicist who now works at an observatory in Hawaii, contends that the Big One — or the Big Ones — can’t be dismissed as myth.
In other words: Trouble is coming.
Since we’ve got quakes on the mind this week, I asked Dvorak about the the special threats facing San Diego and the dueling theories about whether we’ll ever be able to predict when the ground will shake beneath us.
There was been media coverage about how Monday’s L.A. quake is the first in a while up there, and how this may be a sign of something. Is this media hype?
No, not hype. The L.A. region has been seismically quiet for the last few years. Whether this is a statistical fluctuation or has a physical meaning is open to scientific debate. But the region has been unusually quiet recently.
How does the San Diego region fit into California’s earthquake landscape?
Shaking from either the southern San Andreas fault (running from the east side of Salton Sea to north of Palm Springs) or the San Jacinto fault (running southeast from San Bernardino through Riverside and to the west side of the Salton Sea) will cause some damage in San Diego.
What does the San Andreas fault mean to us in San Diego?
Any rupture of the San Andreas fault is going to affect San Diego because it will disrupt infrastructure over a large area somewhere in California.
Even a rupture in Northern California can disrupt cellphone service in San Diego, as well as disturb Internet connections. Communications with banks could be down for an extended period, which means it will not be possible to use a credit card. And transportation will be curtailed because major railways and roadways may be closed.
A rupture of a southern segment of the San Andreas fault will cut off one or more of the five aqueducts that bring 90 percent of the water to Southern California, as well as oil and gas pipelines.
What’s the major earthquake threat we should worry about here in San Diego?
The main concern is the Rose Canyon fault that runs beneath the city of San Diego and northward to Oceanside.
The Rose Canyon fault has been quiet for the last 200 years. But digging into the fault to study prehistoric events shows that the Rose Canyon fault has ruptured in the last few hundred years and can produce large earthquakes.
The big question is whether the Rose Canyon fault is linked to the Newport-Inglewood fault to the north. Do these faults rupture in sequence? And could they rupture simultaneously and break all the way at once from Newport to San Diego? That would be a quake in the mid-7s, magnitude-wise.
I’m not saying that it’s possible. But that’s at the forefront of research.
We have a huge variety of natural features here, from valleys to mountains to canyons, and places like Normal Heights with famously unstable “mudstone” ground that screws up house foundations. How does where you live affect what happens in an earthquake?
Gound that is less compact will shake more than firm ground. This was illustrated in the 1989 Loma Prieta earthquake, when buildings in the Marina district of San Francisco were damaged severely because they were built on loose ground.
The safest place during an earthquake is on solid flat ground. The worst place to be is on a hillside with loose ground.
What should we do to protect public safety?
First, we need to build things — roads, bridges, aqueducts, tunnels, buildings — that will withstand severe seismic shakings, and then have plans to quickly recover the infrastructure — the electric power, the water, the transportation system.
Second, the public should practice — as is done yearly in Japan — what to do in case of an earthquake. Three words: duck, cover and hold on. And realize that the first shaking may not be the last. The 1971 San Fernando earthquake consisted of four distinct shakings over a period of 10 minutes. The 1906 San Francisco earthquake had two shocks. The first lasted about 15 seconds, then a lull of 10 seconds, then the major earthquake that lasted about 45 seconds and that people described as “a freight train hitting a building.”
Third, California needs an early warning seismic system. Such a system in Japan saved many lives and prevented many injuries in March 2011 during the earthquake that produced the tsunami.
Such a system in California would stop elevators so that people could exit, stop trains and buses, automatically turn off valves along gas lines, alert children in schools to get under their desks or tables and so forth.
What is next for earthquake research?
The most crucial question to be answered is: What triggers a large earthquake? There are two divert opinions about this, and it is hotly debated by seismologists.
One theory says all earthquakes begin the same.
Small earthquakes are popping off all the time in California. If a large earthquake is just a small earthquake that grows to a huge size — say, by a cascade of many, many small earthquakes — then there is no hope that large earthquakes will ever be predicted. If so, we will never be able to do anything better than provide probabilities of future earthquakes.
The other theory say the beginning of a large earthquake is fundamentally different from small earthquakes. Perhaps large earthquakes begin by the coordinated sliding of a large segment of a fault such as the San Andreas fault. If so, then large earthquakes might be predicted.