PSN-L Email List Message

Subject: Re: Digest from 08/06/2007 00:01:22
From: "Geoff" gmvoeth@...........
Date: Sat, 11 Aug 2007 10:07:30 -0700

----- Original Message ----- 
Sent: Thursday, August 09, 2007 12:43 PM
Subject: Re: Digest from 08/06/2007 00:01:22

> In a message dated 2007/08/09, gmvoeth@........... writes:
>> It seems unlikely to me that an amatur has the abilities to build 
>> scientific equipment with the abilities to properly recreate the actual ground motion.
> Hi Geoff,
>       Why do you say that? A long period Lehman has a ~flat response out to 
> the edge of the band. The delays due to filters are often ~0.1 sec, maybe a 
> bit more. You tend to get larger delays if you filter below 3Hz
>> There are phase relationships involved that are\very difficult to
>> properly record after passing through complex filter circuits.
>       It largely depends on what filter circuits you use. The Butterworth 
> filters have a sharp phase peak at the band edge. The Bessel filters show a slow 
> change.
>> The best we can hope to achieve are things like
>> first time of arrival and relative energy content.
>       The broad band filters are quite well compensated.
>       You can compensate for time delays in WinQuake.
>       Regards,
>       Chris Chapman   

I really dont know how you can say these things as the
absolute truth unless you are a Physics Major with a PHD
With a degree also in Math to prove your points.
You might very possibly be both of those but because
of the way the USA is and its lack of freedoms
I have no legal way to positively
identify either you or your background.
I only hope you truly understand your subject here.

I see no real delay through circuitry simply
a phase shift like when the wave starts zero degrees
on the input it might come shifted to 90 or 270
degrees on the output. 
It is interesting to note we all live maybe
100 milliseconds behind real time and with
that in mind is it possible at all that we can know the present.

I think because the phase shift is bizarre through the entire spectrum
of any filtered component that a faithful recreation of actual ground
motion is out of reach for the common man.

A square wave ground motion will not be square wave recorded
with a hundred or more of necessary ODD harmonics showing.
As all those harmonics must be in phase with the fundamental.


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