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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