PSN-L Email List Message

Subject: Re: Strange chirps in event data?
From: Larry Conklin lconklin@............
Date: Mon, 25 Jul 2011 10:46:00 -0400


Nothing stupid about the idea, but I don't think that is what is going on.

I maintain a little web page that I use to post interesting events and 
daily drum records from my system  ( 
http://home.roadrunner.com/~lwconklin ).  You can take a look and see 
for yourself that there isn't anything particularly unusual going in in 
the vicinity of the artifacts, which occur just around 04:56 and 05:09 
(in the top window which is band-pass filtered using the Winquake time 
domain filter tool).  And there are four very obvious spikey looking 
transients later in the record for which there is no associated chirp 
artifact.

And, regarding any sort of explanation based on hardware, filtering, 
etc., the question has to be answered "why now?" and "why just this one 
occurrence?".  I haven't changed anything in my system in a long time.

Larry


On 7/24/2011 4:32 PM, gmvoeth wrote:
> 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@............
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