On Fri, 27 Apr 2012 00:55:40 -0700, Hal Murray <[email protected]> wrote:
> >Fun talk at the USGS last (Thur) night: > ShakeAlert! > --building an earthquake early warning system for California > by Doug Given > >He's a good speaker. If you get a chance to hear him, go for it. > http://online.wr.usgs.gov/calendar/ >The video should be up in their archives in a few days. > http://online.wr.usgs.gov/calendar/2012.html >(scroll down to April) > >The basic idea is to detect an earthquake at location X, and then spread the >word using telecommunications. Earthquakes propagate at 2 miles/sec so >phone/internet is much faster. Ballpark is 30-60 seconds of warning. > >The reason this might be interesting for time-nuts is that he mentioned using >GPS to supplement seismometers. The context is that they need the answer in >a few seconds. I didn't catch any details. > >It's unlikely that they are doing any fancy post-processing. I suppose it's >possible that they have streamlined the traditional post-processing setup so >that they can do it in a few seconds. Maybe that is mostly getting an early >look at the data the traditional post-processing processing uses. Through the 80s and 90s I monitored the W6FXN 2 meter amateur radio repeater which was located near Cal Poly Pomona. It was setup to rebroadcast one of the USGS tone modulated seismic sensors when it deviated from rest. The warning time depended on the geometry but was typically 5 to 10 seconds for Orange County since most of the earthquakes like Whittier-Narrows, Loma Prieta, and Northridge originated closer to the seismometer than where I lived. It did not distinguish between local and far earthquakes but you could hear the separation in the S and P waves and tell small from large with a little experience. I also heard the last couple of underground atomic tests. Latency in the warning was on the order of milliseconds. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
