[time-nuts] GPS, USGS Early Earthquake Warning

Brooke Clarke brooke at pacific.net
Sat Apr 28 22:53:32 UTC 2012


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 at pacific.net>
> To: "Tom Van Baak" <tvb at LeapSecond.com>; "Discussion of precise time and frequency measurement" <time-nuts at 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
>
>
>
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