PSN-L Email List Message

Subject: microseisms--especially to those with radio experience
From: Randall Peters PETERS_RD@..........
Date: Sun, 20 Dec 2009 09:59:05 -0500

I am satisfied that there is much more to learn about microseisms than is b=
elieved by those who swear by conventional wisdom.  I got my start in physi=
cs as an amateur radio (ham) operator.  Unfortunately, I failed to renew my=
 general class license years ago (k4ovo).  The radio experience has served =
me well, along with some other physics faculty members that I know.  For ex=
ample, it has caused me to consider the following, which I hope some of you=
 will consider.  The free-oscillations (eigenmodes) of the Earth, in which =
it rings like a bell-- are at frequencies too low to be easily studied by d=
irect means with the instruments which most of us use (not having supercond=
ucting gravimeters).  But I believe there may be a very simple way to study=
 the eigenmodes, using an idea that is basic to radio nearly a century old.=
  Just as intermediate frequencies based on heterodyning are a hallmark of =
radio technology, I have reason to believe (because of nonlinearity) that t=
he eigenmodes modulate the microseisms.  When you look at the typical micro=
seism spectrum, it looks like a broad continuous spectrum.  But it really c=
omprises a large number of fairly short-lived, well defined spectral lines.=
  The difference frequency between adjacent spectral lines appears in nearl=
y every case to correspond to one of the eigenmode frequencies.  The way to=
 see this is as follows--Using WinQuake, filter with a virtually zero bandp=
ass that is centered on the peak of the microseisems.  I have done this by =
setting both high-pass and low-pass at the same value, such as 0.154 Hz, an=
d select 10-poles for the filter characteristic of each.  After doing this =
filter, select 2000-s long individual segments for the x-scale, and then do=
 the FFT for each of these segments.  If under options you select 'arrange'=
, you can look simultaneously at both the time record and the spectrum for =
a given segment.  You will notice that the coherence time of individual mic=
ro's is about 10 to 20 cycles.  As you scan from start to end of a full day=
's record (I use one sample per second for these studies) you will see that=
 the spectrum is a set of sharp spectral lines with small separation freque=
ncies between adjacent lines.  The spacing between these lines changes as y=
ou go from start to finish.  I believe these differences comprise a finite =
set of 'modulation' frequencies that are the Earth's eigenmode set.  Is any=
body interested in checking my hypothesis?  It will take a bit of your time=
 to identify from the spectral lines thus displayed, enough cases to build =
confidence in my claim.=

Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]