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#286381 - 09/21/17 10:46 PM Earthquake Early Warning Systems
hikermor Offline
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 7705
Loc: southern Cal
http://temblor.net/earthquake-insights/will-earthquake-early-warning-work-in-california-5176/

This is a nice summary of the tech involved in earthquake warning systems. Not as much advance notice as one gets for hurricanes, but still way better than nothing....
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#286383 - 09/21/17 11:51 PM Re: Earthquake Early Warning Systems [Re: hikermor]
Russ Offline
Geezer

Registered: 06/02/06
Posts: 5357
Loc: SOCAL
Quote:
...In order to give sufficient warning, the shaking threshold for the alert has to be set very, very low. So, while earthquake early warning could very well save lives and reduce injuries, getting useful alerts comes at a steep cost—and that’s quite apart from money. Most alerts you receive will not be followed by strong shaking, and some shaking will be imperceptible. In these instances, the alert could be considered a nuisance. While the shaking threshold required to trigger an alert could be raised, doing so would increase the “blind zone,” the area in which no warning could be given. So, if you only want to be warned when there will be strong ground shaking (say, because scramming your factory is costly or disruptive), you will almost never be forewarned....

IOW, if you want the warning, be prepared for lots of false alarms. Reducing the false alarms means reducing the time between warning and shaking.

What would you do different if you had 7 seconds heads up?

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#286385 - 09/22/17 01:32 AM Re: Earthquake Early Warning Systems [Re: Russ]
chaosmagnet Offline
Sheriff
Carpal Tunnel

Registered: 12/03/09
Posts: 3842
Loc: USA
Originally Posted By: Russ
What would you do different if you had 7 seconds heads up?


Put on pants and shoes!

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#286390 - 09/22/17 03:26 PM Re: Earthquake Early Warning Systems [Re: chaosmagnet]
adam2 Offline
Addict

Registered: 05/23/08
Posts: 483
Loc: Somerset UK
7 seconds is plenty of time to automatically shut off natural gas and electricity in order to reduce risk of fire.

7 seconds is just about time to automatically open power operated vehicle doors at fire stations, police stations and hospitals. Already opened doors would speed emergency response rather than having to wrestle with doors jammed due to the quake, or inoperable due to power loss.

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#286392 - 09/22/17 03:57 PM Re: Earthquake Early Warning Systems [Re: hikermor]
Pete Offline
Veteran

Registered: 02/20/09
Posts: 1372
One thing that they can't afford - False Alerts.
The system has to be foolproof, and only for major quakes.

I thought the warning time for Los Angeles was closer to 20-30 secs. That's a pretty good warning. If they have sensors at Palm Springs, the warning system will give downtown L.A. about 20-30 secs. But the warning needs to be triggered by multiple sensors, all going off at the same time.

7 secs is enough time to dive for cover.

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#286393 - 09/22/17 04:58 PM Re: Earthquake Early Warning Systems [Re: adam2]
Russ Offline
Geezer

Registered: 06/02/06
Posts: 5357
Loc: SOCAL
If you use that 7 seconds to automatically shut off the natural gas, how do you turn it back on? Once NG is shut off, pilot lights go out and turning it back on means you have a whole lot of homes with natural gas flowing and a pilot light that's not lit. IIRC that's not a good thing.

In my situation, given the likelihood of a high false alarm rate (duh, SOCAL), I'll wait 7 seconds and see what happens.

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#286395 - 09/22/17 05:32 PM Re: Earthquake Early Warning Systems [Re: Russ]
M_a_x Offline
Veteran

Registered: 08/16/02
Posts: 1206
Loc: Germany
I do not know how the installations in the USA are done. In Germany gas heaters and ovens must have a device that shuts off gas flow when the pilot flame is out. The device does not depend on electricity. Itīs often operated by a bimetal strip. Turning back on NG does not cause any issues with those installations.
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#286396 - 09/22/17 05:38 PM Re: Earthquake Early Warning Systems [Re: M_a_x]
Tjin Offline
Pooh-Bah

Registered: 04/08/02
Posts: 1821
Originally Posted By: M_a_x
I do not know how the installations in the USA are done. In Germany gas heaters and ovens must have a device that shuts off gas flow when the pilot flame is out. The device does not depend on electricity. Itīs often operated by a bimetal strip. Turning back on NG does not cause any issues with those installations.


But there are so many old stoves and gas ovens that do not have them. The main 200bar gasline will not even be shut off here for a leak, untill a diversion has been placed, so the gaslines will hold pressure.
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#286398 - 09/22/17 06:36 PM Re: Earthquake Early Warning Systems [Re: Tjin]
hikermor Offline
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 7705
Loc: southern Cal
Bi metal strip shuoffs are routine in the USA. Over the years, i have experienced several interruptions in gas service and flowing gas has not been a problem, although it can sometimes be tricky to get those pilot lights going again.

I think I would use my seven seconds to drop and cover or take other preventive actions (stop operating power tools, etc). If it should be false alarm in that I didn't experience a severe jolt, that's OK - preferable to a complete surprise...

There is an automatic gas shut off valve which is installed at the service box. That should be serviced, after actuation, by a gas company representative.


Edited by hikermor (09/22/17 06:38 PM)
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#286401 - 09/22/17 07:41 PM Re: Earthquake Early Warning Systems [Re: hikermor]
Russ Offline
Geezer

Registered: 06/02/06
Posts: 5357
Loc: SOCAL
I stand corrected. Still, 7 seconds after the warning, I'll still be wondering if it's another false alarm . . . . . . . Yup.

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