Hi Brett
I stopped the 0.002 hz high pass in SDR when I installed my new enclosure. I may 
have run a 0.002 hz high pass in Winquake. I re-acquired the data and the only 
difference in the trace is what I would call temperature change during the 12 
hrs. That low frequency half cycle is not in your data. The unfiltered fft 
amplitude was 20% @ 0.001 hz and 15% @ 0.002 hz.. The presumably filtered fft 
data you got was  ~13% @ 0.001 hz and ~10% @ 0.002 hz.

 Regards
Barry






________________________________
From: Brett Nordgren 
To: psnlist@..............
Sent: Thu, March 17, 2011 2:38:24 PM
Subject: Re: The  Earth is Ringing - oh yes

Gary,

From the data Barry sent, I plotted his FFT (blue) along with red lines marking 
the frequencies of some spheroidal normal earth modes, and you see peaks at most 
of them, from 0S10 up to mode 0S49 and probably some more.  That's quite amazing 
when you consider that the seismometer's velocity senstivity to 0S10, with its 
9.7 minute period, is down by a factor of around 135 from the mid-band 
sensitivity.  The earth was ringing indeed.  I assume there was a 0.002 Hz 
one-pole high pass (8.33 minutes) so it probably helped eliminate any traces of 
the longer-period modes.  


http://bnordgren.org/seismo/110311.120000.ch1.fft.pdf

Looks great,

Brett


At 09:17 PM 3/11/2011, you wrote:

After 19 hours the earth's ring is starting to subside. I measure a period of 
about 240 seconds or so. Is that the period of the earth's natural frequency. 
All day my vertical seismometer's most sensitive output has been ringing like a 
bell. It's difficult to see through the output of the initial M8.9 quake and all 
the aftershocks.
>Gary
>  
>Gary Lindgren
>585 Lincoln Ave
>Palo Alto CA 94301
> 
>650-326-0655
> 
>www.blue-eagle-technologies.com   Check out Lastest Seismometer Reading
>cymonsplace.blogspot.com 
>sites.google.com/site/seismicsensorinfo/Home    Design Details for New Vertical 
>Seismometer  

Hi Brett
I stopped the 0.002 hz high pass in SDR when I installed my new enclosure. I may have run a 0.002 hz high pass in Winquake. I re-acquired the data and the only difference in the trace is what I would call temperature change during the 12 hrs. That low frequency half cycle is not in your data. The unfiltered fft amplitude was 20% @ 0.001 hz and 15% @ 0.002 hz.. The presumably filtered fft data you got was  ~13% @ 0.001 hz and ~10% @ 0.002 hz.
 
Regards
Barry



From: Brett Nordgren
 <brett3nt@.............>
To: psnlist@..............
Sent: Thu, March 17, 2011 2:38:24 PM
Subject: Re: The
 Earth is Ringing - oh yes




Gary,


 From the data Barry sent, I plotted his FFT (blue) along with red lines
marking the frequencies of some spheroidal normal earth modes, and you
see peaks at most of them, from
0S10 up to mode
0S49 and probably some
more.  That's quite amazing when you consider that the seismometer's
velocity senstivity to 0S10, with
its 9.7 minute period, is down by a factor of around 135 from the
mid-band sensitivity.  The earth was ringing indeed.  I assume
there was a 0.002 Hz one-pole high pass (8.33 minutes) so it probably
helped eliminate any traces of the longer-period modes.  



http://bnordgren.org/seismo/110311.120000.ch1.fft.pdf


Looks great,


Brett




At 09:17 PM 3/11/2011, you wrote:

After 19 hours the earth's ring
is starting to subside. I measure a period of about 240 seconds or so. Is
that the period of the earth's natural frequency. All day my vertical
seismometer's most sensitive output has been ringing like a bell. It's
difficult to see through the output of the initial M8.9 quake and all the
aftershocks.

Gary

  

Gary Lindgren

585 Lincoln Ave

Palo Alto CA 94301

 

650-326-0655

 


www.blue-eagle-technologies.com   Check out Lastest
Seismometer Reading


cymonsplace.blogspot.com 


sites.google.com/site/seismicsensorinfo/Home    Design
Details for New Vertical Seismometer