5 ms·
It works well for Mexico, but would not be as useful in California. Earthquake P-waves travel at 5km/s. To get 60 seconds of warning, you must be 300km (186 mi
by cjensen 9y ago
It works well for Mexico, but would not be as useful in California.
Earthquake P-waves travel at 5km/s. To get 60 seconds of warning, you must be 300km (186 miles) downstream of the detector.
Mexico has a very unique situation [1]: the filled lake basins that Mexico City sits on have the same resonance frequency as buildings of a certain height. Earthquakes generate that frequency. So a serious earthquake 300km away can get the lake basin rocking, and that will knock down buildings of a certain height.
A detector is nowhere near as useful in California. Consider the Loma Prieta Earthquake. It occurred 90km from the damaged sections of San Francisco. Assuming there is a detector within 10km of Loma Prieta, that is only 16 seconds of warning. Give a few seconds for the alert to get out, and it's barely 10 seconds. That's not enough time to do anything other than hide under a desk -- which you can already do after the earthquake starts. Such a system would be excellent for bringing trains to a halt, but that's pretty much it.
[1] See preface of https://en.wikipedia.org/wiki/1985_Mexico_City_earthquake https://en.wikipedia.org/wiki/1985_Mexico_City_earthquake
- dllthomas 9y agoGiven the opportunity, I know I'd rather be ten seconds further from a nearby stack of bricks or possibly-unsecured bookcase when an earthquake hits...
- rripken 9y agoIsn't that enough time to start to slow BART trains?
- jdavis703 9y agoThis is enough time for automated systems to have an orderly shutdown. Trains come to a stop so they don't derail. Toll both gates on bridges go down. Fire station doors open up. Elavators stop on the nearest floor and open their doors.
- aylons 9y agoThanks for the explanation. However, it may be nowhere as useful, but still plenty useful. On the top of my head, 10s could be enough so: * Trains may stop, preventing a literal train wreck. * People doing delicate tasks (e.g., a surgeon, someone operating heavy machinery, even someone cooking) may lock to a safer position. * Elevators may stop and open the doors safely, so no one will be stuck inside them. * Air traffic control may hold take offs and maybe landings. * All traffic lights going red may slightly reduce car incidents. Seems minor, I admit. Also, people with little experience (me!) do NOT understand that an earthquake is happening until after the fact. Some blast alert even during the earthquake is very helpful for tourists and even immigrants.
- flashman 9y agoHere's a video of Japan's warning system giving someone 30+ seconds of notice before the 2011 earthquake: https://www.youtube.com/watch?v=n-FMpNBfna8 https://www.youtube.com/watch?v=n-FMpNBfna8 (and notice how significant the shaking was, even at that distance) Here's another example of what you can do with ten seconds: https://www.youtube.com/watch?v=gB6-nU2nJqM https://www.youtube.com/watch?v=gB6-nU2nJqM
- rrauenza 9y agoWhy do you suppose she props the door open with the chair? Because building shifts could jame it closed via the door frame?
- level3 9y agoYes, there have been cases of people getting trapped in rooms/buildings due to doors getting bent or warped, so it’s common advice in Japan to prop open a door to secure yourself an exit.
- casefields 9y agoThat's just Triangle of Life nonsense. https://en.wikipedia.org/wiki/Triangle_of_Life https://en.wikipedia.org/wiki/Triangle_of_Life https://www.snopes.com/fact-check/triangle-of-life/ https://www.snopes.com/fact-check/triangle-of-life/
- mehrdadn 9y agoI hate these "it wouldn't help" arguments regarding most things in this world, including this one. Case in point here, even a siren blasting 0 seconds beforehand would be useful to reduce the inevitable delay between when you feel something shaking and when you realize it's really an earthquake. I'm not sure where you're getting the idea that it wouldn't be useful, because as far as I know, the reason we don't have it is lack of funding, not lack of usefulness.
- cjensen 9y agoI did not way "it wouldn't help". At all. I said that it super-helps Mexico, but that because of the specific situations in both regions, we should not anticipate getting anything like their results.
- beojan 9y ago> Such a system would be excellent for bringing trains to a halt, but that's pretty much it. You could also cut off gas and water lines, so it would probably prevent a lot of damage due fire or flooding.
- e40 9y agoI would bet the average time to turn off the gas line to a random house would be more than 10 minutes. Probably much more.