Fault System Enables Larger Quakes In California

Taco Cowboy writes Researchers have mapped the land at the southern end of the Hayward Fault and found that the creep continued 15 km beyond to merge with the Calaveras Fault, which was thought to be independent. "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. 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, but there is one problem — the estimate was 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.

Comments

Drought solution

[Dan East]

One step closer to significantly reducing California's water consumption.

Re:Drought solution

[hawguy]

Please, for your own safety, do not come to California. The Bike One is right around the corner, as it has been for as long as anyone living can remember, so, if you move here, you will falll into the oceania, and die. (And wee don't need any more people driving our land prices up.)

That doesn't change the fact that the big one *is* right around the corner, it will come, lives will be lost, hundreds of billions of dollars in direct costs may be incurred, and taxpayers will be paying much of those costs in disaster aid since many homeowners are uninsured, and even for those that are, the funds backing their insurance may run out in a large quake.

Though I guess building a large metropolis on top of known earthquake faults is no worse than using flood disaster funds to build right back in the flood plain.

Re:Drought solution

[ShanghaiBill]

For the people who are in California, I assume getting earthquake insurance, if financially feasible, would be best, right?

If you live in a single family wood frame house, as most people in the East Bay do, then an earthquake on the Hayward/Calaveras Fault is not that big of a threat. The oscillations from a quake are a threat to big buildings, and bridges, but the resonance doesn't affect small structures as much. Most houses in the area are built with Hardy Frames, or some other seismic reinforcement. The biggest threat is not the quake itself, but fire, caused by broken gas lines, and hard to extinguish if the water lines are also broken. So stockpile some water jugs, clear dead trees and debris, and replace your wood shank roof with shingles or tile. Wood shank roofs were banned in new construction after the 1991 Oakland Firestorm, but some older houses in the area still have them.

Only in California!

[Anonymous Coward]

Really, a fault system that makes your problems worse?

C'mon California, learn to program!

Re:Only in California!

[Megane]

But is it known to cause cancer?

Pffff... Magnitude 7?

[Anonymous Coward]

Here by law anything you build has to withstand a 8.0 without structural damage. We don't even count the ones below 7.

Regards from Chile.

Re:Pffff... Magnitude 7?

[kit_triforce]

Laws requiring all structures to withstand an 8.0? Let's move past the enforcement nightmare that would be and look at the reality of building that strong, It would cost close to million US dollars to build a single floor, single family dwelling to those specifications. You would need a foundation between 36"-48", fully steel enforced, likely 6"x12" studs throughout 16" on center and 12'x12' or larger corner posts. The roof structure would weigh 5 to 7 times what a normal roof would, and every single wood joint would have to be reinforced with 1" thick steel plate, bolted through the stud and beam centers.

In California structural laws are designed to preserve human life, and structures are designed to survive the shaking enough to allow people to exit, but we take the Japanese mentality that natural disasters will do damage, and it's better to rebuild every few decades.

Besides, California is a transverse zone (primarily, north of Mendocino is subduction with divergent off shore, and some divergence from the Salton Sea south) and we deal with shallow M7-M9 earthquakes, while Chile runs along a subduction zone, with deep M15+ quakes. Your quakes have much more energy dispersed over a larger area, while ours tend to be more localized and focused. We get at most 3-5 minutes of shaking, with less than a minute of intense damaging waves, while you can have 5min+ of building-toppling destruction,

Re:Pffff... Magnitude 7?

[LynnwoodRooster]

Interesting... That certainly wasn't the case back in the mid 2000s. At least for the shanty town on the side of the road down to Valparaiso. I loved my time living in Chile (Vina del Mar, Valparaiso, Renaca), and it's easily the best country in South America to live in, but there was certainly a lot of shoddy construction quality...

Re:Pffff... Magnitude 7?

[beelsebob]

You realise that the way you (intelligently) make buildings survive large earthquakes is not to build ridiculously strong foundations (those actually make your problems worse). Instead, it's to design the building to move and sway with the earthquake. Hence why any large office building built today in the bay area is likely to be sat on big rollers, and/or have a weight system on the roof to damp the building.

Re:Pffff... Magnitude 7?

[kit_triforce]

Try living in the area and building in the area before you start speaking of things you seem to know nothing about.

Well, my home is within 10 miles of the San Andreas Fault, and my work is built entirely within the historical San Andreas fault zone (my office lies less than 1/2 mile from the current southern branch). I am a native Californian and have ridden out many earthquakes, both in and out of school.

And to address other concerns, the Field Act is insufficient for the high end for potential quakes. It it designed to handle M7 quakes, while historical data shows that a M7.9 has occurred in California. Note that the strongest quakes since 1933 were 2 M7.3. My research in getting my BA in geology showed that up to about a M9 could theoretically be possible, and that the historical data may be underestimated (the 1812 Wrightwood-area earthquake had one report suggesting a possible M9.2).

Also, I was generally estimating the design, but I was also referring to low one story buildings, as opposed to multiple floor structures. Larger buildings require a very different approach to their foundations (in order to reduce oscillation). The original statement said "withstand a 8.0 without structural damage" and while a M8.0 off a subduction zone is no where near as powerful as a M8.0 off a transverse zone at the surface, I seriously doubt that any country has the economics to build to such a high standard across the board.

Quake

[ls671]

Some Californian found a bug in quake that enables you to make your game environment larger?

Re:Yes

[PPH]

Some day soon, everything east of the San Andreas fault is going to break off and slide into the Atlantic Ocean.

Re:Yes

[Anonymous Coward]

Don't feel bad, it doesn't make the national news much: but from over pumping ground water here in Florida we now have sink holes everywhere (http://www.wsj.com/articles/SB10001424052702304172404575169014291111050). Saltwater is creeping much faster than anyone previously thought, and our springs are already all polluted (except literally a handful out of hundreds), and as if being polluted isn't enough, they are all *going dry* or have already dried up (http://www.tampabay.com/news/environment/water/floridas-vanishing-springs/1262988). Oh, and because we have no elevation anywhere and lax environmental laws on ag, ALL of our surface water is considered contaminated. Hiking in true wilderness here (what's left of it), is nearly as difficult as it is in SoCal desert with its near zero surface water. But, the voters here can't remember any more than what the last TV ad spot told them.

Re:dumbass sciantust's

[Mr D from 63]

clueless idiot. Learn what a log scale is...

Obviously its for weighing lumber.