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
http://neic.usgs.gov/neis/eqlists/eqstats.html 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
Public Seismic Network Mailing List (PSN-L)
[ Top ]
[ Back ]
[ Home Page ]