PSN-L Email List Message

Subject: Re: ARRIVAL TIMES: Quiet Before The Storm
From: Thomas Dick dickthomas01@.............
Date: Fri, 04 Sep 2009 10:52:14 -0500

I can't argue with you (all of your comments) and I don't have the 
professional equipment that you do and I am not as educated:
1. Do you remember the antique spinning tops (and this tells my age).... 
the very old screw toy spinning top that you could push down on and it 
would spin. If you pushed down enough, it would "sing" and if this top 
hit a bad place in the floor or a piece of would skip 
acrossed the floor. Suppose the spinning earth is possibly "singing" 
(all the time).Now, the earth certainly doesn't have dirt to cause it to 
go bump but external forces and even large blocks of material within the 
liquid core of the earth might move and cause it vibrate. Add the 
possible effect of the changing tilt of the earth as it moves through 
its orbit and  even large areal changes in surface temperature, tides 
and even surface winds could be an issue. You can see this when blowing 
on some of the new battery operated spinning tops.

2. and may I ask this question ..... is it time that you (everyone) step 
back from looking at the tree itself(earthquake) and spend time looking 
at the forest (natural "noise" that the earth makes)? Maybe no noise is 
as important a clue as the everyday "noise" that your the seismic unit 
"sees". Maybe your equipment has progressed to the point that it is 
detecting more than the earthquakes that bought you to this point. Maybe 
you are on the brink of going into a new realm of investigation that 
could help predict earthquakes?

rsparks wrote:
> The quiet period before the arrival of a quake may be an illusion.
> Our seismic detectors always detect something, and that something is 
> always a sine wave.  (We will ignore that the background may contain 
> waves of several frequencies)  Now when the energy from a quake 
> arrives, it will add to the energy already coming from the background 
> sine waves.  As a result, at the beginning of the quake signal, you 
> are beginning the process of adding two waves together.
> Now consider that the new second wave can begin at any time in the 
> life of the background wave.  If the two waves are of the same 
> frequency, it is possible for the two waves to be of exactly the same 
> frequency and phase, so that the sum of the waves would appear to be a 
> smooth increase of amplitude, all at one frequency.  The two waves 
> must be exactly synchronized for this to occur but it is done all the 
> time in the power industry when a new generator is connected to the 
> grid. 
> More likely the quake wave will join the background wave out of 
> phase.  This will make it difficult to tell exactly when the new wave 
> begins because the background wave is unlikely to be zero amplitude.  
> We must remove the background wave to learn exactly the time of 
> arrival of the new wave.
> Any quiet period before the second wave arrival may be an illusion 
> resulting from arrival occurring during a peak and seemingly level 
> time period for the background wave.  The inverse could also happen 
> where the arrival coincided with the peak rate of change of the 
> background wave, with the result that the second wave appears to 
> arrive EARLIER than true arrive time (an illusion).
> Reasonable?
> Roger
> Subject: ARRIVAL TIMES: Quiet Before The Storm
> From:    "Geoffrey" 
> Date:    Wed, 2 Sep 2009 17:50:11 -0700
> I have noticed in some Earthquakes you seem to notice
> a short increase in quietness just before the impulse arrives.
> Is this a real phenomena or simply a coincidence ?
> Does this mean the real arrival time is
> the beginning of the noticeable quiet ?
> What physics would possibly muffle the noise ?
> arrival of Possibly eP instead of simply P ?
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