Hi Ted,

I would probably be instructive for you to look at the helicorder 
record from the COR station that is posted 
here:  http://jclahr.com/science/psn/cor/index.html
Click on the image to toggle between three different filter settings.

The station is an EXPENSIVE broad band station of the sort used for 
seismological research.  Unless an earthquake is HUGE on this record, 
I will not see it on my AS-1 educational station.

Cheers,
John

At 02:07 PM 3/5/2008, you wrote:
>Hi All,   Perhaps someone can explain the different in recorded 
>data, between a (let's say a Lehman) at 2 second period and the same 
>sensor at 20 seconds.
>
>I have compared data from two such sensors.   Here is what I have 
>found, but I am sure I am understanding the TRUE difference.
>
>I get smaller EQ's on the shorter periods,  my guess is about 1/3 
>more events.   Mainly on the closer EQ's or smaller EQ's for the 2 
>second machine.
>
>That is not to say the 20 second period machine, does not pick these 
>up, just not as many, if they are weak.
>
>If it is a big event I get it on both machines equally?   If it is a 
>medium event I get it on both machines.  But, if it is weak, 
>definitely better on the 2 second machine.
>
>About the only difference, I can see on the 20 second machine traces 
>is the duration.   On a 8.0M the 20 second trace could be three 
>hours long on the 2 second machine maybe only one hour.
>
>I do understand the teleseismic, traveling greater distances, loses 
>the higher frequencies, and those remaining can be in the range of 
>10-20 seconds.
>However I pick up the teleseismic very well on the 2 second machine, 
>they are  just not as long in duration.
>
>Thanks, Ted


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