Steinar,  Yes that's a mystery...You may wish to make a list of things it 
could be and things it can't be.

I don't think it is a natural event.
I don't think it is a train.
I don't think it is weather.
I don't think it is someone walking around.
I don't think it is a small appliance, like a hand drill, or refrigerator.

I do think it is a man made machine.
I do think it is on a timer.
I do think it is within a mile or so.

Does it continue day and night?
Is it a new noise?

Ted





----- Original Message ----- 
From: "Steinar Midtskogen" 
To: 
Sent: Thursday, September 11, 2008 2:36 AM
Subject: Strange geophone pattern


>I have a Mark Products 4.5 Hz 3 component L15B geophone, and since the
> two major earthquakes in Indonesia and Hokkaido happened during the
> night here when the local noise is low, I thought it would be
> interesting to see whether such quakes show up at all on a geophone.
>
> Apparently, they didn't, but I found a strange pattern repeating every
> 25 minutes:
>
> http://voksenlia.net/met/seismometer/geo.jpg
>
> Does anyone have any ideas what could cause this?
>
> Perhaps an airconditioner two floors above?  Then it seems to run
> through some kind of program that I wasn't aware of.  Or perhaps a
> neighbour runnings some kind of machinery going through cycles?
>
> The datalogger is fanless and diskless, so it shouldn't cause any
> vibrations.
>
> -- 
> Steinar
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