PSN-L Email List Message
Subject: Re: Strange chirps in event data?
From: Larry Conklin lconklin@............
Date: Sat, 23 Jul 2011 16:36:17 -0400
Well, whatever it is that I'm seeing, I'm very sure it has nothing to do
with the quake. The signal isn't natural looking at all. It is a
nearly sinusoidal wave that begins pretty abruptly, sweeps down in
frequency from 2 hz to 0.4 hz and then stops fairly abruptly. I have a
history of similar artifacts that have showed up from time to time, but
I don't think they have shown this sort of frequency sweep before. That
is what caught my interest this time. In past occurrences I would see a
minute or so of a very pure looking tone that would show up in the FFT
plot as a very narrow spike around 2 hz. I'd love to know what's going
on, but don't have much of an idea of how to run it down.
Larry
> both of my Leymans show a sharp spike about 25 seconds before S
> arrival here in Evansville, IN...largest spike occurred on my E-W unit
> it is visible on the N-S and vertical AS-1 to lesser extent.
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