This may sound stupid, but it sounds like
an impulse response of your electronocs.

If you check the FFT and see a response similar
to the design of your electronics Id say
either an impulse of an electrical nature
or possibly the geophone has shocked your system.
It appears as an impulse followed by an ever increasing Period.
Slowly dying.

----- Original Message ----- 
From: "Larry Conklin" 
To: "PSN List" 
Sent: Saturday, July 23, 2011 10:19 AM
Subject: Strange chirps in event data?


>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@............
> __________________________________________________________
> 
> Public Seismic Network Mailing List (PSNLIST)
> 
> To leave this list email PSNLIST-REQUEST@.............. with 
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
>
__________________________________________________________

Public Seismic Network Mailing List (PSNLIST)

To leave this list email PSNLIST-REQUEST@.............. with 
the body of the message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more information.