PSN-L Email List Message

Subject: Re: Instument Quality
From: Brett Nordgren brett3nt@.............
Date: Fri, 23 Oct 2009 11:18:09 -0400


At 07:11 AM 10/23/2009 -0600, you wrote:
>I have a follow up question, only somewhat related.   When the sensor is 
>completed, one of the first questions a novice might ask is "What can I 
>expect to see"?     I know this would depend, not only the sensor, but 
>many other things, like the location, and the other components of the station.

I agree that it depends on a lot of things other than the sensor 
quality.  For the smaller quakes, the fault orientation and depth are also 
important.  Some that are "pointed" properly and not too deep can come in 
strongly, while others of the same magnitude and distance will not be visible.

Using the worldwide statistics from   I get, roughly:

M 8+  1/ year
M 7+  1/ 3 weeks
M 6+  3/ week
M 5+  4/ day
M 4+  1.7/ hour

As noted, the rate for the lower magnitudes should be reduced to eliminate 
quakes which are not oriented well or too deep to generate surface waves, 
and depending on where I am located, adjusted to favor those quakes which 
are closer.  I have the impression that fault orientation may be 
considerably more important than distance.

If my instrument and site allow me to see Mag 7's, I may be waiting weeks 
to see something.  If it can see half of all the Mag. 5's, I will probably 
be seeing a couple a day.  That would be my strongest argument for working 
to have the best setup possible--lots more action.

Dave (California) Nelson's vertical will see the surface waves from a few 
in the high 4's and many in the 5's.
See the link below:

Curiously, the ANMO Albuquerque borehole seismo, considered to be among the 
best, sometimes doesn't see as much as the home-built instrument.  They 
apparently are using a 20-second *low pass* filter for their helicorder 
trace, which often cuts out quite a lot which would otherwise be seen with 
less agressive filtering.


Watch our wiggles

or watch some very very good wiggles


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