Hayward fault "locked and loaded" for 6.7-7.0 earthquake

[David]

Originally Posted by irishgrl

thats easy. he's formulating jabborwock type messages that will keep us all entertained until the next century.......maybe.

I no Jabborwock!!

Here's what Susan Hough (USGS) says about the Hayward Fault:

"In the East Bay, the Hayward Fault is thought to be capable of generating earthquakes upwards of M7, & it runs through the heart of Oakland & Berkeley. Because ground motions immediately adjacent to a fault rupture are known to be especially severe, the hazard associated with the Hayward Fault is substantial because of the high population density immediately along the fault."

Hough says later on:

"Is California prepared for the many Big Ones that it ultimately will face? Relatively speaking, the answer is yes. The state's building codes & standards are among the best in the world. Yet the fact remains that California has not been tested by the worst that the earth can produce. California has not faced a Big One since the state emerged as the most populous in the nation, home to a diverse & increasingly high-tech economy."

Susan Hough's point is a good one: The last "Big One" in California was the 1906 quake, which was about a magnitude 7.8, more or less. The city of San Francisco was highly populated in 1906, but I'm not sure the surrounding region was. It certainly wasn't to the extent it is today. Bigger population generally means more casualties & more damage, obviously. (The biggest quake in California recorded history -- in 1857 -- only killed five or six people because practically nobody lived in that region yet.)

If I lived in the Bay Area (including East Bay & South Bay, with their San Andreas, Hayward, Calaveras & other faults), I'd take some steps to prepare for medium & large quakes.

San Andreas can generate much larger magnitude quakes than Hayward (remember that longer rupture equals greater magnitude), but an M6.5 to M7 is big! It will kill people & it will damage infrastructure.

I don't know whether the entire Hayward Fault is expected to unzip in a single event, though (which sounds like what happened in 1868 to generate an M6.9).

[irishgrl]

(The biggest quake in California recorded history -- in 1857 -- only killed five or six people because practically nobody lived in that region yet.)

And wasnt that the Hayward fault that produced it? The point about population leading to higher damage costs is very true. Damage COSTS are increasing with the population which is why all of these disaster issues are to be taken seriously (unlike Bush and co.). California has improved its building codes but there are plenty of old buildings that were never retrofitted.
And that poor lady in the article who has to patch and paint every year....eventually she will reach a point where her house will split in two. And you cant get earthquake insurance in some parts of CA, which I think is a shame...

[David]

Originally Posted by irishgrl

And wasnt that the Hayward fault that produced it?

No, that was the Fort Tejon Quake of '57 on the San Andreas. Moment magnitude derived in recent years from that is about 8.0, which is kinda too big for the Hayward Fault, as I say. The Hayward Fault isn't long enough to generate an 8. Earthquakes rupture a patch along a fault's surface. Generally speaking, the larger the rupture patch, the larger the magnitude of the earthquake. All faults are inherently limited by their length. When Hayward ruptured in 1868, the USGS says the rupture went from Agua Caliente Creek area northerly to San Leandro (http://quake.wr.usgs.gov/prepare/ncep/hayward.html) & possibly farther. This is I guess about 50 to 60 kilometers, which might be the max that any single segment of the Hayward Fault can slip. I'm really not sure--you have to read those USGS pages & read books like "Earthshaking Science" by Susan Hough. But as you can see from that USGS page, there is uncertainty among seismologists about just how big a quake the Hayward Fault can generate in one event: some of them say about Mw6.8 & some of them say possibly higher than Mw7.0 (& some in between).

But who needs an 8 or a 7.5 to be a real problem? A smaller quake is a BAD MUTHA in such a densely populated region of the state, especially if it's shallow like the Hayward. The Hayward Fault has shallow fault depths. This means that even a small quake can break windows, make chimneys fall & create serious disturbance inside home; & a medium-sized quake can kill a lot of people & rip up lots of the buildings.

If I were living in some of those colorful little towns that straddle parts of the fault, or lie adjacent to the fault zone, I'd have plenty of earthquake insurance & I'd prepare as much as possible.

The point about population leading to higher damage costs is very true. Damage COSTS are increasing with the population which is why all of these disaster issues are to be taken seriously (unlike Bush and co.). California has improved its building codes but there are plenty of old buildings that were never retrofitted.

Yep, & you'd better worry if you work in a brick building, too. They can reinforce brick buildings with those angle brackets & other things, but the way you join one brick to another is with cement, & cement doesn't bend much in an earthquake.

The other day, I secured all my carnival glass to my curio shelves with that gummy stuff you stick underneath each piece. I live on a big granite mountain, so earthquakes just feel like single sharp jolts up here. I don't have to content with much duration in movement, the way people do who live on alluvium. Site response is the name of the game.

[irishgrl]

Originally Posted by David

No, that was the Fort Tejon Quake of '57 on the San Andreas. Moment magnitude derived in recent years from that is about 8.0, which is kinda too big for the Hayward Fault, as I say. The Hayward Fault isn't long enough to generate an 8.

but my original article said the Hayward fault had an earthquake in 1857 that killed 5 or 6 people I thought it was the same one?

EDIT: oops, wrong year, but right death count.......

Before San Francisco's Great Quake of 1906, on the San Andreas fault, there was the Great Quake of 1868 on the Hayward, a magnitude 6.9 rumbler that killed five people. Severe quakes have happened on the Hayward Fault every 151 years, give or take 23 years, meaning it is now into the danger zone.