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San Andreas fault capable of magnitude 8.1 earthquake over 340-mile swath of California, researchers say [Updated]

San andreas The "Big One" on the San Andreas fault just got a little bigger.

New research showing a section of the fault is long overdue for a major earthquake has some scientists saying that the fault is capable of a magnitude 8.1 earthquake that could run 340 miles from Monterey County to the Salton Sea. 

Whether such a quake would happen in our lifetime had been a subject of hot debate among scientists. That's because experts had believed that a major section of the southern San Andreas, which runs through the Carrizo Plain 100 miles northwest of Los Angeles, would remain dormant for at least another century.

But that rosy hypothesis seemed to be shattered by a recent report in the journal Geology, which said that even that section of the San Andreas is far overdue for the "Big One." [Updated, Oct. 9: The report, published in August, was written by Sinan Akciz and Lisa Grant Ludwig of UC Irvine, and J. Ramon Arrowsmith and Olaf Zielke of Arizona State University.]

Now, according to U.S. Geological Survey seismologist Lucy Jones, it is entirely possible that all 340 miles of the southern San Andreas could be ready to erupt at any time. Such a scenario would trigger a magnitude 8.1 earthquake, said Thomas Jordan, director of the Southern California Earthquake Center, a calculation with which Jones agreed.

"All of it has plenty enough stress for it to be ready to go," Jones said. "The biggest implication of [the report] is that it increases the likelihood that when we do have a big earthquake, it will grow into the 'wall-to-wall' rupture."

[Updated, Oct. 9: Such a temblor could cause much more damage because with a longer stretch of the fault rupturing, a larger area is exposed to the quake, and the shaking would last longer.]

The walls Jones is referring to are the boundaries of the southern San Andreas, which begins in the Salton Sea and ends in the town of Parkfield in Monterey County. Scientists consider the southern San Andreas fault as one segment generally because it behaves the same -- it rarely rumbles, but when awakened, the shaking can be devastating.

In contrast, the section of the San Andreas north of Parkfield up to Hollister in San Benito County behaves differently. That section constantly moves at a creep -- meaning stress is relieved regularly, so large quakes don't occur there.

Large quakes haven't occurred anywhere on the southern San Andreas for more than a century, making it a sleeping giant that has been building stress for so long it could snap at any moment.

"My concern is that we will get a series of large earthquakes along the San Andreas fault," Jordan said. The last "Big One" to rip through Southern California occurred in 1857, when an estimated magnitude-7.9-quake, ruptured 200 miles of fault between Monterey and San Bernardino counties. It wasn't a wall-to-wall quake: It stopped near the Cajon Pass, near the present-day 15 Freeway, probably because the fault south of it shook just a few decades earlier, in 1812, Jones said. Because the 1812 quake had relieved tectonic tension in that area, it effectively put a brake to the 1857 quake from moving further south.

But with the San Bernardino County section of the fault now having accumulated two centuries' worth of strain, there may not be any brakes now. "Can I imagine the 1857 earthquake happening again and stopping at the Cajon Pass? Probably not," Jones said. "Once you have a big slip, you're more likely to move along down the fault," Jones said. "If the rupture has been made ... that’s a lot of momentum that will keep the rupture moving down the fault."

The San Andreas has long been considered one of the most dangerous faults in Southern California because of its length. Not only do longer faults produce bigger quakes, they emit a type of shaking energy that can travel longer distances.

"So a much larger area is affected by a really large earthquake," Jones said.

In 2008, seismologists developed a scenario for a large earthquake on the San Andreas -- a magnitude 7.8 shaker that begins at the Salton Sea and barrels northwest along the fault toward San Bernardino and Los Angeles counties.

-- Rong-Gong Lin II

Photo: Quake researchers study a portion of the San Andreas fault. Ricardo DeAratanha / Los Angeles Times; Map: U.S. Geological Survey

Comments () | Archives (46)

Paleez! Where is the sanity of Kate Hutton? Lucy Jones is a grant-seeking catastrophist. Where are the corollaries of today? What of the '89 Lomo Prieta quake? How about the '06 Frisco quake? Why were they not "wall-to-wall?" The 1857 Ft. Tejon quake was big that, Jones concedes, was not "wall-to-wall." So she has no corollary.

This is easy conjecture that gets Jones' name in print. It is a crock. Quakes are real. "Wall-to-wall?" That regards shag carpeting, not the San Andreas. Paleez.

The fault is cabable of at least 8.1.
The freeways are capable of sustaining about a 5.5 (sustained shaking)

So I guess what I'm saying is Los Angeles is living in a fantasy if we think we can get out of here after a devastating earthquake. People can't even drive when it rains without screwing up traffic, tailgating, texting, etc. The freeways will be choked and/or closed, so we should be prepared with food, water, flashlights, furst aid kit, etc. because if an 8.0 hits you aren't going to be able to go anywhere for supplies coz driving will be next to impossible.

We are one of the most susceptible cities with the least preparedness.

When an 8.0 hits L.A. it will be interesting to see how we will handle it.
We'll probably be too busy shooting at rioters/smash n' grab looters to leave our homes anyway. I know I sure will :)

I remember the first time Lucy was on TV after a quake. She looked like she'd just got out bed. The second time she took two hours to put on her make-up and get her hair done before appearing on TV. I guess she misses the attention.

That's why I have dirtbikes....

So, two months ago the studies printed in Geology magazine claimed that earthquakes along the southern section of the San Andreas had occurred more frequently than scientists thought.

However, that news was offset by the claim in that same article that perhaps not all earthquakes along the southern section had carried "Big One"- type magnitudes, with some of those quakes measuring in the mid to high sixes, which are still scary but eminently survivable.

Now, two months later, we're hearing that we could have a "wall to wall" 340 miles catastrophe.

On top of all this, there are some geologists who claim that the southern section is experiencing a natural lull.

The bottom line is, whether it happens in one minute or one hundred years from now, you have to be prepared. Have a kit, have a plan, and find something solid to get under and hang on to.

And always remember, "If it bleeds, it leads." Everybody, be they newspapers or geologists, are trying to sell something.

If an 8.1 hits California maybe it will shake some of the illegals up on out of Cali and residents inland will have beach front property...and the part of Cali that broke off will be an island...maybe where the illegals are LOL

This is sort of controversial in the field. Likely if such an event described would occur the rupture passed the unpinned area of the SA Fault would likely be categorized as separate earthquake.

An 8.1 Moment Magnitude is considerably larger than the 7.8 Magnitude of either the San Francisco or Fort Tejon Quakes. Comparing earthquakes gets confusing because people use different definitions "Magnitude."

Rockwater, yeah what about those other quakes? That's what Lucy Jones does for her job. To see how the earth moves. We may be dead by the time this earthquake hits but I'm sure your grandchildren will ride this one. If it's a crock where's your data to support otherwise. Are you also filling your own cavaties or do you go to a dentist? A 340 mile long fault line is not a crock. Dormancy on that line is real. Quake prediction is not. She never said when exactly, she just said it would happen. So maybe in 2012, eh?

BYE - BYE California!!!

This large quake WILL happen, and probably soon. It may be even larger than 8.1. It will be PART of the nation's judgement for all of its sins.
Mark it down. Bank it.

Does it matter? After the big one hits California will be just like Katrina and Haiti. Fend for yourself if you even survive.

Lucy is talking about surface rupture of the fault- that is what will be "wall-to-wall" when/if the fault pops at that 8.1 she is talking about. This article isn't about a bunch of 8.1 earthquakes happening at the same time up the entire section of the fault. The main event is capable of happening on any section of the fault south of Parkfield to Mexico. We care about rupture because of the infrastructure that is built on or near the fault. It will all be displaced.

I'm against this sort of thing.

Woohoo! Let she shaking begin!

It will happen within someone's lifetime.

Would the Hollywood area be severely affected by this anticipated 8.1?

The quake will hit on Dec. 21, 2012. Party now, because we'll all be goners.

perhaps we should set off a series of nukes buried under the fault to get the ball rollin'...

If it happens, the tea wing nuts will call it Obama's Fault.

California will be so much better off when the big one hits causing the cancerous tumor west of the fault to fall off and sink into the Pacific.

That woman running along the fault NEEDS TO SLOW DOWN BEFORE SHE FALLS IN!

See this is what I have been telling everyone for the past 2 years and everyone says I'm a quack. No I'm not, I have a math degree and 3 other degrees. I'm just retired that's all and hate to see my kids get in the path of this coming monster because those idiots at the USGS have been telling everyone lies for years to protect the value of their own properties.

Nothing we can do about anyway, 'when it happens it happens.' I'm prepared with the necessities, I worry fire though and emergency response and whether there will be major injuries with response time for them.
The Long Beach quake in 1933 had many fires and San Francisco, that worries me the most. I hope I'm at home, downstairs and that's it's daylight when it happens.

I guess a good thing is that with millions of homes destroyed that will increase demand for homes across the nation for a good while!!

"The 1857 Ft. Tejon quake was big that, Jones concedes, was not "wall-to-wall." So she has no corollary."

200 miles or 340 miles; all the same, the destruction will be enormous and widespread over the southern California region.

But the point being, that the frequency is 100 years, whereas the current period has exceeded that frequency and has built up stress, points to the possibility of stress being relieved all along the 340 miles, once this baby gets going.

You must be Republican; I sense a disdain for science.

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