LOS ANGELES — For decades, scientists have assumed the central portion of California’s San Andreas fault acts as a barrier that prevents a big quake in the southern part of the state from spreading to the north, and vice versa. As a result, a mega-quake that could be felt from San Diego to San Francisco was widely considered impossible.
But that key fault segment might not serve as a barrier in all cases, researchers wrote Wednesday in the online edition of the journal Nature.
Using a combination of laboratory measurements and computer simulations, the two scientists showed how so-called creeping segments in a fault — long thought to be benign because they slip slowly and steadily along as tectonic plates shift — might behave like locked segments, which build up stress over time and then rupture.
Such a snap caused the 9.0-magnitude Tohoku-Oki earthquake that hit Japan in 2011, triggering a tsunami, killing nearly 16,000 people and destroying the Fukushima Daiichi nuclear power plant. Forecasters had not believed such a large quake was possible there.
A supposedly stable section of fault also ruptured during the 1999 Chi-Chi quake in Taiwan, a 7.6-magnitude temblor that killed more than 2,400 people.
Afterward, scientists drilled into rocks surrounding the Chelungpu fault there, removing samples and testing them to better understand their geology.
Caltech engineer and geophysicist Nadia Lapusta and a former postdoctoral fellow, Hiroyuki Noda of the Japan Agency for Marine-Earth Science and Technology in Yokohama, used that data in their analysis published in Nature.
They plugged the measured rock properties into a computer model they built that simulated a simple fault with two “patches” of rock — one that was locked and another that was creeping.
As expected, most of the time only the locked patch ruptured. But there were also instances when the simulation resulted in ruptures in the creeping patch. In those cases, the rocks slipped past each other quickly enough to heat up and weaken the fault, allowing it to snap.
The results provide a possible explanation for events that caused the Tohoku-Oki and Chi-Chi quakes, which have puzzled scientists. By extension, they also suggest that the San Andreas might be capable of a more extensive earthquake than was widely assumed.
“The thinking has been that an earthquake could either occur on the southern San Andreas fault or on the northern San Andreas fault — that the creeping segment is separating it into two halves,” Lapusta said. “But this study shows that if an earthquake penetrates that creeping area in a certain way, it could rupture through it.”
The San Andreas wouldn’t necessarily snap as the fault in the model did, she said: “Hopefully the creeping segment is such that it doesn’t have the propensity for weakness. But without examining further, you can’t say.”
Such an investigation might include further computer simulations, laboratory experiments or digging along the creeping portion of the San Andreas to look for evidence of extremely large slips in the ancient past.
By looking at a fault relatively close to its surface — no more than tens of yards deep — paleogeologists can see whether very large earthquakes ever ruptured through to the surface, Lapusta said. Scientists can also drill to greater depths to collect rock samples, as they did to study the Chelungpu fault.
Kenneth Hudnut, a geophysicist at the U.S. Geological Survey in Pasadena who was not involved in the research, said that the study sounded “a warning message.”
“We’re realizing we need to worry more about these things we’ve been calling barriers,” he said, adding that the Tohoku-Oki quake wasn’t the only recent disaster making researchers reconsider fault segments once thought to be “toothless” — temblors in the Indian Ocean, Chile, Haiti and China had also given pause.
“The more big earthquakes we’ve seen around the world, the more we’ve realized that there are some deficiencies in our models,” he said. “Everyone’s taking a second look at what we thought was worst-case.”
Hudnut emphasized that an extreme quake powerful enough to blast through the supposedly stable midsection of the San Andreas was unlikely.
But if one did strike, he said, it might put unexpected strain on California’s emergency response systems. Planners had always assumed that responders from one part of the state would be available to supply aid in the other.
-Los Angeles Times
mike dawson
Los Angles and San Francisco would disapear……….Think of all the democrats that would be lost……………
brian
that would be hella cool qnd bad ass
Guest
Take out all Democrats and all Union members that have been earthquake like to this State!
Rush Limpbaull
while the fat republican slobs sit back, watch and masturbate themselves into a near coma frenzy……
Domi-Domi
Shut the freak up about politics already! Is there not one fckng comment box in the United States that even respond to the actually story? Who are you dipshits who are subjecting all of us to the torture of reading your unintelligent political BS?
Sam
Thank you! I was just posting on a website to report robocall telemarketers and the thread was all about Obama. Seriously, we've lost our collective minds.
Sam
Oh good, just when we survived the Mayan apocalypse, they revive "THE BIG ONE"! Woohoo, glad I just paid my earthquake insurance.
melbaback
before I looked at the check 4 $5228, I did not believe …that…my best friend had been actualey earning money in there spare time from there labtop.. there uncle started doing this for less than six months and just repaid the loans on their place and purchased a brand new Smart ForTwo. this is where I went,……… BIT40.ℂOℳ
VNgrunt67
Time to buy some prime beach-front property in Fresno/Bakersfield!
TommyLee
Right on.
fprex scam
Felix Homogratus, Dimitri Chavkerov Rules! You pay us we post good about us!!