From: Steinar Midtskogen 
To: psnlist 
Sent: Fri, 22 Feb 2013 7:13
Subject: Re: Chelyabinsk


Hi Chris,

>    The CTBT web site shows a broad spectrum of waves up to well over
> 3 Hz. I would have expected there to be some pressure wave signals
> showing up on your Lehman, but they would have arrived well before the
> sound signal. Did you check ? A 1 Hz geophone, or an extended range
> 4.5 Hz geophone might have shown something.

I only checked my 4.5 Hz geophones, since I would expect that
frequency to be closer to what to expect than the range of the Lehman.
So I just checked the Lehman.  What I have is moderately noisy,
probably due to windy condition on the west coast of Norway 500 km
away.  There's nothing standing out, except one blip at 06:31UTC.

 http://norskmeteornettverk.no/bilder/seismo_20130215.jpg

I was looking for something lasting a little while, not something sub
second, but on the other hand I have no idea what to expect from a
fireball event.  The geophones do not have this blip at the same time.

I think the meteor event happened at 03:22UTC (but I've seen various
statements).  The distance is roughly 3000 km.  So 06:31UTC seems much
to late anyway.  If the Lehman is sensitive to small barometric
changes, such blips are more likely caused by someone opening or
closing a door elsewhere in the house, I presume.

Hi Steinar,

    My apologies for the delayed reply - I have been visiting my other
house for maintenance ~ 220 km away.
     A Lehman is hardly effected at all by barometric changes, but can=20
and
will pick up horizontal vibrations like slamming a door.
     The P wave velocity is about 6 km / sec for near surface and about=20
8 km
/ sec for mantle waves. A 3000 km track could be expected to take about=20
6
to 9 miutes, so you should look at 03.28 to 03.31 UTC for direct=20
seismic
signals. Atomic weapons produce quite a large signal, even air blasts,=20
but
like earthquakes, only seismic frequencies below ~2 Hz are likely to be
propagated.
    I hope that this will help !

    Regards,

     Chris Chapman
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