Scientists say the Big One could be even bigger

An aerial view of the San Andreas fault in the Carrizo Plain, Central California. Image: USGS, Wikimedia Commons.

The Big One predicted for the San Andreas fault could end up being bigger than earthquake experts previously thought.

New research shows that a section of the fault is long overdue for a major earthquake.

Some scientists are saying that the southern portion of the fault is capable of a magnitude 8.1 earthquake that could run 340 miles.

That would be significantly stronger and wider than the southern San Andreas' last major rupture, in 1857. Such an earthquake could cause much more damage because its power would be spread over a larger area and the shaking would last longer.

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

But that seemed to be shattered by a recent report in the journal Geology, which said that even that section is far overdue for a major quake.

According to U.S. Geological Survey Lucy Jones, all 340 miles of the southern San Andreas could rupture.

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.

"My concern is that we will get a series of large earthquakes along the ," Jordan said.

Jones refers to such a huge earthquake as "wall-to-wall" because it would cover a wide area of Southern California.

The "walls" of the southern San Andreas begin in the and end in 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 fault north of Parkfield behaves differently. That section moves at a constant creep; because stress is relieved regularly, large quakes don't occur there.

In 1857, 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 around the Cajon Pass, probably because the fault south of that area had ruptured just a few decades earlier, in 1812, Jones said. Because the 1812 quake had relieved tectonic tension in the Cajon Pass, it effectively stopped the 1857 from moving further south.

"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, but their shaking also emits a type of energy that can travel longer distances.

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

Explore further

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User comments

Oct 11, 2010
"I've a suggestion to keep you all occupied... learn to swim."


Oct 11, 2010
I live like 10 min from the Cajon Pass so I'm curious to what is in store for me shall an earthquake that big come rumbling on by. Fingers crossed ;)

Oct 11, 2010
Physika --> see Pyles comment. A big plus of course is that all those wonderful hills and mountains will be on top of you instead of underneath you, so swimming will probably be a secondary concern.

Oct 11, 2010
Doesn't it seem Scientists have become Jeremiads, constantly...?

Oct 12, 2010
Doesn't it seem Scientists have become Jeremiads, constantly...??

Oct 12, 2010
"Doesn't it seem Scientists have become Jeremiads, constantly...??"

uh.. no? It's a scientists job to speculate, hypothesize, then research and confirm or throw out ideas. The problem doesn't lie with scientists but the idiot styled masses who don't know how to differentiate between "this might happen so just fyi" and "oh god the sky is falling"! Would you rather scientists just do and say nothing? Sometimes things do happen that are bad for people and sometimes researchers do identify some of those things before they become problems. Putting your head in the sand won't save you from an earthquake I am sorry to say.

Oct 12, 2010
Doesn't it seem Scientists have become Jeremiads, constantly...??

Unlike ANY other group of people in society (like religious leaders, politicians, actors, musicians, businessmen, etc.), when scientists give opinions like this, those opinions are based on evidence and observations that have been painstakingly gathered over much of their careers, not on their own "beliefs" or anything. A scientist might seem like a "jeremiad", but if they do it is only because the reality of the situation calls for it. If you disagree it is because you are an idiot and you clearly don't understand what science is.

Oct 12, 2010
"Some say the end is near. Some say we'll see Armageddon soon.

I've a suggestion to keep you all occupied... learn to swim."

Personally, I like this line the best:

"See you down at Arizona Bay."

Maybe not too many people here know that song.

On a more serious note: Earthquakes fascinate me because they are so hard to really get my brain around. It's one of those natural phenom that happen on a scale that's way outside normal human experience. I have a hard time conceptualizing the amount of energy that must be released in a large quake. I mean, moving an entire continent with enough violence that it actually shakes the whole planet. How do you shake a planet? That's an insane amount of energy.

Oct 12, 2010
In the Los Angeles geologic area, there is a jumble of faults, unlike the San Andreas both north and south of there. While the fault named "San Andreas" runs east of the LA Basin, no one knows how all of that jumble is related deep underground. Think of it as a big ball of rock straddling the San Andreas and fractured in numerous planes at odds with each other.
Is is a safe bet to say that that fault system is locked. It is probably safe to say that that area is building stress at many levels of the crust and in numerous directions.
When a major fracture occurs in that 'jumble of basalt rock', it will release immense forces in many directions. It is not unlikely that the San Andreas both north and south will also move, as well as many of the other adjacent faults under Los Angeles.
Got your earthquake supplies ready?
No, there won't be any great subsidence. No, the ocean won't pour in and drown the population. But there will be great destruction and loss of lives.

Oct 17, 2010
I've always wanted to live in the Pacific north west. That's why I'm buying up acreage in North Dakota

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