PSN-L Email List Message

Subject: Re: Strange chirps in event data?
From: Thomas Dick dickthomas01@.............
Date: Sat, 23 Jul 2011 14:09:47 -0500


On 7/23/2011 12:19 PM, Larry Conklin wrote:
> I was looking over the data I recorded overnight from the 6.5 quake 
> off Japan.  In the process I applied a band-pass filter (0.4 - 2.0 hz) 
> to see what, if anything, would show up.  What showed up were two 
> strange "chirps" that are all but hidden in the noise.  I wouldn't 
> have noticed them except for the fact that the first occurred a little 
> before the arrival time of the S wave.  I don't believe that they have 
> anything to do with the quake.  But I have no idea and no theory for 
> what did cause them.
>
> They are substantially identical, lasting for about a minute and 20 
> seconds each, and decending from around 2 hz to .4 hz.  (Hmmmm.... 
> just noticed the obvious correlation with my filter limits.)  Trouble 
> is, without the filter, the signals are indistinguishable in the 
> overall background.  But, I made sound files from both the filtered 
> and unfiltered data, and the chirps are obvious in both versions and 
> sound virtually identical.  So, the filter may be truncating the ends 
> a little, but looks like it is more or less a lucky fit to the data.
>
> I'd be interested in whatever speculative explanations anybody may 
> have to offer.  My system is an SG sensor based on Larry's electronics 
> board, and the data was recorded from the high frequency channel.  
> I've seen some similar artifacts in my data before, but didn't 
> recognize how odd they were.
>
> If anyone is sufficiently curious, I'd be happy to e-mail them copies 
> of the filtered and unfiltered event file data, along with the .wav 
> files I made.
>
> Larry Conklin
> lconklin@............
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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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