Newly discovered link between Calaveras, Hayward faults means potentially larger quakes

Newly discovered link between Calaveras, Hayward faults means potentially larger quakes
The Bay Area fault system and the spot (red star) where the Hayward Fault branches off from the Calaveras Fault. The white lines indicate faults recognized by the USGS. The red line is the newly discovered surface trace connecting the southern end of the Hayward Fault to the Calaveras Fault, once thought to be an independent system. The surface trace is offset by several kilometers from the deep portion of the fault 3-5 km below ground (blue line). Credit: Estelle Chaussard, UC Berkeley

University of California, Berkeley seismologists have proven that the Hayward Fault is essentially a branch of the Calaveras Fault that runs east of San Jose, which means that both could rupture together, resulting in a significantly more destructive earthquake than previously thought.

"The maximum earthquake on a fault is proportional to its length, so by having the two directly connected, we can have a rupture propagating across from one to the other, making a larger quake," said lead researcher Estelle Chaussard, a postdoctoral fellow in the Berkeley Seismological Laboratory. "People have been looking for evidence of this for a long time, but only now do we have the data to prove it."

The 70-kilometer-long Hayward Fault is already known as one of the most dangerous in the country because it runs through large population areas from its northern limit on San Pablo Bay at Richmond to its southern end south of Fremont.

In an update of seismic hazards last month, the U.S. Geological Survey estimated a 14.3 percent likelihood of a magnitude 6.7 or greater earthquake on the Hayward Fault in the next 30 years, and a 7.4 percent chance on the Calaveras Fault.

These are based on the assumption that the two faults are independent systems, and that the maximum quake on the Hayward Fault would be between magnitudes 6.9 and 7.0. Given that the Hayward and Calaveras faults are connected, the energy released in a simultaneous rupture could be 2.5 times greater, or a magnitude 7.3 quake.

"A rupture from Richmond to Gilroy would produce about a 7.3 magnitude quake, but it would be even greater if the rupture extended south to Hollister, where the Calaveras Fault meets the San Andreas Fault," Chaussard said.

Chaussard and her colleagues, including Roland Bürgmann, a UC Berkeley professor of earth and planetary science, reported their findings today (April 2) in the journal Geophysical Research Letters.

Creep connects two faults

Chaussard said there has always been ambiguity about whether the two faults are connected. The Hayward Fault ends just short of the Calaveras Fault, which runs about 123 kilometers from north of Danville south to Hollister in the Salinas Valley.

The UC Berkeley team used 19 years of satellite data to map ground deformation using interferometric synthetic aperture radar (InSAR) and measure creep along the southern end of the Hayward Fault, and found, surprisingly, that the creep didn't stop south of Fremont, the presumed southern end of the fault, but continued as far as the Calaveras Fault.

"We found that it continued on another 15 kilometers and that the trace merged with the trace of the Calaveras Fault," she said. In addition, seismic data show that micro-earthquakes on these faults 3-5 kilometers underground also merge. "With this evidence from surface creep and seismicity, we can argue for a direct junction on the surface and at depth for the two faults."

Both are strike-slip faults - the western side moves northward relative to the eastern side. The researchers found that the underground portion of the Hayward Fault meets the Calaveras Fault 10 kilometers farther north than where the creeping surface traces of both faults meet. This geometry implies that the Hayward Fault dips at an angle where it meets the Calaveras Fault.

InSAR revolutionizes mapping

Chaussard said that the many years of InSAR data, in particular from the European Space Agency's ERS and Envisat satellites from 1992 to 2011, were critical to connecting the two faults.

Creep, or the surface movement along a fault, is evidenced by offset curbs, streets and home foundations. It is normally determined by measuring points on opposite sides of a fault every few years, but that is hard to do along an entire fault or in difficult terrain. InSAR provides data over large areas even in vegetated terrains and outside of urban areas, and with the repeated measurements over many years InSAR can detect deformation with a precision of 2 millimeters per year.

"With InSAR, we have access to much larger spatial coverage," said Chaussard, who has been expanding the use of InSAR to measure water resources and now ground deformation that occurs between earthquakes. "Instead of having a few points, we have over 200,000 points in the Bay Area. And we have access to areas we couldn't go to on the ground."

She noted that while creep relieves stress on a fault gradually, eventually the surface movement must catch up with the long-term underground fault movement. The Hayward Fault moves at about 10 millimeters per year underground, but it creeps at only 3 to 8 millimeters per year. Earthquakes occur when the surface suddenly catches up with a 's underground long-term movement.

"Creep is delaying the accumulation of stress needed to get to an earthquake, but it does not cancel the earthquake," Chaussard said.


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Journal information: Geophysical Research Letters

Citation: Newly discovered link between Calaveras, Hayward faults means potentially larger quakes (2015, April 3) retrieved 22 October 2019 from https://phys.org/news/2015-04-newly-link-calaveras-hayward-faults.html
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Apr 03, 2015
Like I say, Hollywood is never wrong.
http://youtu.be/yftHosO0eUo

Apr 03, 2015
We had a small one a few miles away two days ago. There was no difference in arrival between the P and S waves, so it was within a few miles, about 20.

I am within a dozen miles of those faults,and expect a real ride. The ground rolled like ocean waves during Loma Prieta.

Still, I would rather live here with the dangers than cower elsewhere.

Apr 03, 2015
"Like I say, Hollywood is never wrong."
----------------------------------------

Oh,really?

Do you believe Frank Sinatra, Sylvester Stallone, Marion Morrison (aka John Wayne), and the other draft-dodging cowards were real heroes?

Did you serve?

Apr 03, 2015
otto, sorry about the snark.

Let's keep it in science today.

Mea culpa.

Apr 03, 2015
otto, sorry about the snark.

Let's keep it in science today.

Mea culpa.
I told you mea farrow, you want civil dialogue youve got to own up to all your bullshit. And refrain from posting any more. And I doubt that's possible.

Apr 03, 2015
Okay, Hollywood is right,

Do you believe Frank Sinatra, Sylvester Stallone, Marion Morrison (aka John Wayne), and the other draft-dodging cowards were real heroes?

Did LA have its volcano yet?


Apr 04, 2015
I spent 10 years in the SF bay area and there's nothing there worth anything. The people there deny their heritage is vested in capitalism and they profess what amounts to communal living. Common courtesy doesn't exist, and personal entitlement is the norm.

California seriously should release everything north of the line from Salinas through Bridgeport to the hoped-for state of Jefferson, and seat the government of California in Temecula.

Let the lunatics run their asylum, not mine.

Apr 04, 2015
Okay, Hollywood is right,

Do you believe Frank Sinatra, Sylvester Stallone, Marion Morrison (aka John Wayne), and the other draft-dodging cowards were real heroes?

Did LA have its volcano yet?

I believe that people who are caught lying and making up their own facts are cowards when they can't own up to it.

Apr 04, 2015
"I spent 10 years in the SF bay area and there's nothing there worth anything. The people there deny their heritage is vested in capitalism and they profess what amounts to communal living"
-----------------------------------------------

Yeah, we appreciate Nature and other good folk here. No as much blind Capitalism and extreme selfishness.

Go live with otto and 166

Apr 04, 2015
The more I read abecedarian, the funnier he gets. World leaders just sent their best and brightest and their ministers to the US to see how we do the inventing the future thing. They went to San Francisco and Silicon Valley. Not where abecedarian lives.

Detroit car makers are opening new design bureaus, . . in Silicon Valley, where I used to work. . Soon, we will be showing the industries where abecedarian lives how to do things.

Apr 04, 2015
"I believe that people who are caught lying and making up their own facts are cowards when they can't own up to it."
-------------------------------------

No coward here, otto, I enlisted and volunteered for the War of My Generation, while you hid from it.

Apr 04, 2015
otto, I also changed my mind about the war while I was in it, and made it loudly known. It was unappreciated, and I wound up in the hospital twice, but showed more courage than you will ever have.

Apr 04, 2015
gkam admitted:
Still, I would rather live here with the dangers than cower elsewhere.


Precisely the attitude you criticize in "deniers", proving once again that there is no difference in the behavior of AGWites and skeptics. The difference is that AGWites want to impose behavior on OTHER people, behavior they do not adopt themselves. He admits directly that SURE DISASTER is not a reason to change one's behavior, all the while demanding doctrinal conformity from skeptics. ROFLMAO We should agree. Then we can tut-tut and drive around, burn energy, breed and act *exactly the same*. But we won't be denying trolls.

Thanks, gkam. You've totally shown your side for their true colors!

Now to the USGS data and the phone book. Fingers crossed.

Apr 04, 2015
Twist any any of my statements all you want, like 166, but you're still silly.

Nope, you can still heat your house with coal, but cannot let the emissions pollute my environment. You can eat yourself fat, or skinny, think whatever you want, make funny gestures and sounds to imaginary beings, all of it, . . . but do not bother the rest of us.

If you want to own a coal powerplant, fine. Go do it. But the days of polluting the worlds of others is coming to a close. Clean it up or shut it down. You can smoke all you want, but keep it inside, for your own pleasure.

Thanks.


Apr 04, 2015
"I spent 10 years in the SF bay area and there's nothing there worth anything. The people there deny their heritage is vested in capitalism and they profess what amounts to communal living"
-----------------------------------------------

Yeah, we appreciate Nature and other good folk here. No as much blind Capitalism and extreme selfishness.

Go live with otto and 166


Is "here" San Ramone, or Cali? Because San Ramone is the most banal American capitalist city I've ever seen. The Aggies have corrupted your mind. Or is "nature" watching plastic float down the ditch to Stockton???

Apr 04, 2015
Yeah, real credibility, . . for someone who does not even know how to spell San Ramon.

And we don't care what you've seen.

Apr 04, 2015
It's also worth noting that natives of the area have talked about the two faults being correlated for years and years and the experts have always condescendingly explained that it doesn't work that way, that faults are independent. Reminiscent of the "pandas aren't bears" lecture that one got for decades. Until genome sequencing came along. "Oh, they're bears that lost the ability to smell meat". Don't ever once remember an apology and they have the gall to start the retraction with "We now know...".

Maybe someday also with the local concept of "earthquake weather". There's definitely a correlation between low pressure systems and major earthquakes. What put out the great SF fire? Rain. Guess there was low pressure around. lol Maybe the trees act like sails in the wind and the shallow faults move! Bone to the rabid pseudo-science crowd this site draws. See if I've got the formula.

Apr 04, 2015
[q

Maybe someday also with the local concept of "earthquake weather". There's definitely a correlation between low pressure systems and major earthquakes.

That's one Great lying Whopper.

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