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An Early Warning System For Earthquakes
Iphtashu Fitz writes "Would 15 seconds be enough warning time to prepare for an earthquake? It certainly wouldn't be long enough to evacuate from where you live, but it may be just long enough to get out of a building or brace yourself in a doorframe or under a solid desk. Italian scientists may have discovered a way to measure the initial shockwave of an earthquake two seconds after it starts, and from it predict the extent of the destructive secondary wave that will follow. It typically takes twenty seconds for the secondary wave to spread 40 miles, so sensors that can transmit warnings at the speed of light may provide just enough warning before a major quake for people to brace themselves. Even more importantly, such a warning could allow for utilities like gas companies to close safety valves, preventing potential fires or explosions in the aftermath of the quake."
"Wouldn't it take one really powerful earthquake for you to need to take cover 40 miles from the epicenter?"
Yes.
Our house is about 20 miles from epicenter of the 1994 Northridge quake, the most costly quake ever recorded ( California housing is expensive ), and it was not damaged at all. I don't recall Oakland or Berkeley suffering much from the SF earthquake in the 90s, and they are less than 40 miles away.
According to http://home.att.net/~srschmitt/script_earthquake.h tml -- 1a 100km damage zone is common for earthquakes around 6.1-6.9 on the Richter scale, so 40 miles is a reasonable damage zone. I have no idea on the 20 seconds/40 miles measurement however.
It's never just a game when you're winning. - George Carlin
The epicenter of the Kashmir earthquake (2005, Pakistan & India, 7.6) was 62 miles (100km) away from Islamabad and yet it knocked an apartment building down.
Sig is on vacation
"... brace yourself in a doorframe ..."
this is a myth. The only thing this acomplishes is broken fingers.
It stems from an observation from a red cross worker after a earthquake in mexico.(I think 1950ish.)
That archtecture of the entrance way was an adobe arch. Arches are very strong, as opposed wooden square door frames.
The Kruger Dunning explains most post on
Possibly it would prevent the continued flow of gas to the pipe. Some would still leak, but either the gas would burn out quickly or dissipate before it's ignited.
The collapsed Cyprus freeway was in Oakland. It's believed that earthquake waves travel horizontally through the crust and can also be reflected off of harder layers further down. If the original wave and the reflected wave harmonize they can be extremely destructive even many miles from the epicenter.
It's simple: I demand prosecution for torture.
ElarmS.
While the article is quite light on details, much work has been done in this area, by groups such as ElarmS in California, if your interested in the methodology take a look at Allen's paper "Rapid magnitude determination for earthquake early warning (a 7 pg. PDF) which is reasonable understandable by lay persons if you skip through the math, yet still informative for people in the field.
Apocalypse Cancelled, Sorry, No Ticket Refunds
The epicenter of the 1989 Loma Prieta earthquake was in the Santa Cruz mountains, about 60 miles south of San Francisco and Oakland. Some of the worst damage was in these areas. The "Cypress Structure" of the I-880 freeway collapsed, as did a portion of the Bay Bridge. In the town, another 20 miles north of Oakland, I lived in at the time there was considerable damage to some older structures as well as to personal property.
I would have been happy to have the 15 seconds notice.
I have seen more 2x8s or 10s (usually short pieces from the scrap pile after the sills or rafters are put in) used as the headers in doorways. And being on edge, then over the studs, that makes doorways much stronger than the rest of the wall, even though the gap is larger. I don't think just a 2x4 slapped sideways on top flies many places any more for code, geez, not for decdes maybe. I know some places have almost no code, but just simple framing tends to be almost universal.
Mexico City is built on top of an ancient swamp and the soil liquifies during earthquakes.
Good building codes wouldn't have been enough.
Nothing to see here; Move along.
It really all depends on what types of crust your epicenter and surrounding areas are, along with depth of the epicenter. Crust content surrounding an epicenter can also increase or decrease wave displacement, direction, and force. Giving a maximum distance for initial or secondary waves, can only be estimated based on the recorded seismic history of a given area and the surrounding crust, any estimate are in fact only that. Living in Southern Cali myself, I can tell you, I have felt quakes for 60+ miles, of course they felt like someone walking with lead feet in the house and no damage what so ever, but the fact that it was felt is a good example that they can travel farther.
-- Brought to you by Carl's JR
Our house is about 20 miles from epicenter of the 1994 Northridge quake
Then apparently you were lucky.
BTW, that 1990s quake, was 1989. And damage was severe upwards of 50 miles away, if you check here.
BTW, its epicenter was closer to Santa Cruz, so it did a lot of damage considering it travelled nearly 50+ miles to reach the bay.
"Some days you just can't get rid of a bomb."
I think this damage mitigation is the basic idea. It's almost impossible to prevent a rupture, but should it rupture, you don't want gas to continually push through it. Gas often dissipates very quickly, but if it has a constant supply and happen to have a spark nearby, then it's asking for trouble that could have been avoided if you had shut-off valves.