Ted,

In my earlier posting, I forgot to mention noise from the seismometer 
itself.

Every moving contact point will generate friction and noise.   Friction 
is noise.  Low friction is low noise.

Severe seismometer noise is observed as a "spikey" trace, rather than 
the smooth wave form that should be seen as a result of the ocean noise. 
  Less severe seismometer noise will appear as small spikes on an 
undulating ocean wave, but a smooth ocean wave trace can never be 
observed.

On my vertical seismometer, I have eliminated seismometer friction noise 
by using long springs as the hinge.  I still have seismometer noise that 
could be called "phase" noise that is a result of seismometer damping 
and motion characteristics.

Sorry to have omitted this noise source from my previous posting.

Roger
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