[time-nuts] GPS, USGS Early Earthquake Warning

Jim Lux jimlux at earthlink.net
Sat Apr 28 23:34:06 UTC 2012


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.





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