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


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