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" <bro...@pacific.net>
To: "Tom Van Baak" <t...@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
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