On 4/28/12 3:32 PM, Tom Van Baak wrote: > Related to that, are there any seismometer experts on the list? I've > always wondered why they don't augment the extremely sensitive > detectors with less sensitive detectors? Of course a really good > detector will overload; so just co-locate cheap detectors that are 40 > and 80 dB less sensitive. That way you get a clean signal no matter > how close or far the epicenter is from the detector. > here in southern California they have what they call "strong motion" stations which are exactly what you describe. (and probably other places, I just happen to know about the one that is co-located with a regular station near where I live, because you can see the data online). A lot of these are colocated with SCIGN stations (which have geodetic quality GPS stations). The sensors have maximums of several G as I recall. I think the peak accelerations in 94 were around 1 G or a bit over. That is, stuff, like houses, literally got launched into the air, as opposed to just shaken til collapse. And of course, structural resonance effects amplify it substantially. There was a bigger push to get them going after Loma Prieta and Jan 94 Northridge, as I recall, because structure and other damage had "hot spots" (due to various propagation effects across the santa monica mountains, for instance), and they wanted better knowledge in a (certain to occur) future event.

In the early 1980's I visited the dominion radio astronomy observatory in Canada. I observed a bunker like structure and asked my host what it contained, he advised me that it housed a special seismograph that would only be of use in the event of a large earth quake. Sent from my iPod On 2012-04-28, at 3:53 PM, Brooke Clarke <brooke@pacific.net> wrote: > Hi Tom: > > They do use two different seismometers at each location, a large movement and a sensitive. > http://www.prc68.com/I/Seismometer.shtml > > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/Clarke4Congress.html > > > Tom Van Baak wrote: >> Brooke, >> >> Right, an overloaded accelerometer is a problem -- if you have >> only one or a few of them. >> >> But the beauty of using cellular sites is that you have hundreds >> or thousands of them across populated areas; so it's no problem >> if the a bunch of sensors near the epicenter overload. A clipped >> signal is not worthless; at least you know something big happened >> there; you can rely on slightly more distant cell tower sensors to >> get readings a few seconds later that are less clipped or not clipped >> at all. (There's another solution I heard about -- using smartphones >> as a tiered network of synchronized accelerometers). >> >> A high rate GPS solution sounds really cool to me but I bet its also >> far more expensive. >> >> Related to that, are there any seismometer experts on the list? I've >> always wondered why they don't augment the extremely sensitive >> detectors with less sensitive detectors? Of course a really good >> detector will overload; so just co-locate cheap detectors that are 40 >> and 80 dB less sensitive. That way you get a clean signal no matter >> how close or far the epicenter is from the detector. >> >> /tvb >> >> ----- Original Message ----- From: "Brooke Clarke" <brooke@pacific.net> >> To: "Tom Van Baak" <tvb@LeapSecond.com>; "Discussion of precise time and frequency measurement" <time-nuts@febo.com> >> Sent: Saturday, April 28, 2012 2:49 PM >> Subject: Re: [time-nuts] GPS, USGS Early Earthquake Warning >> >> >>> Hi Tom: >>> >>> The USGS talk was the first time I'd heard about the need to look at an earthquake as happening along some length of fault line. For the big quake in Japan the forecast software assumed a point source for the quake and that cause them to under estimate the magnitude and get other things wrong. GPS is part of the solution to get better results. >>> >>> In the S. CA example he showed a 180 mile long rupture of the San Andreas fault. At 2 miles a second the quake would last about 90 seconds. >>> Accelerometers that are not right on top of the fault will be overloaded with signals coming from each location where there's a fracture and so the data will be nearly impossible to untangle in a short time frame. But a GPS receiver will show a DC displacement that unambiguous. >>> >>> Have Fun, >>> >>> Brooke Clarke >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

http://quakealarm.com/
http://www.inertialsensor.com/inertial-navigation-accelerometers.php

 Björn

Hi Brooke, > Hi Tom: > > They do use two different seismometers at each location, a large movement > and a sensitive. > http://www.prc68.com/I/Seismometer.shtml > > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/Clarke4Congress.html It is a bit fun that the Earthquake Detector product "QA-2000" shares product name with the Honeywell (Sundstrand) Inertial accelerometer "QA-2000"... http://quakealarm.com/ http://www.inertialsensor.com/inertial-navigation-accelerometers.php -- Björn

I enjoyed the talk, thanks to the OP for pointing it out. Of course, I would have liked more detail on the GPS! 73, David GM8ARV -- SatSignal software - quality software written to your requirements Web: http://www.satsignal.eu Email: david-taylor@blueyonder.co.uk