From: Steinar Midtskogen steinar@.............
Subject: Re: Lehman seismometer movement


By extrapolating http://jclahr.com/science/psn/magnitude.html we
hould expect about 2 cm (!) ground movement at this distance, but I
xpect that this would be longer periods than what my Lehman was
esigned for.
While my observation might be plausible I'm actually more impressed
ith what I saw on my 4.5 Hz geophones.  Here's what I get if I apply
 1 Hz lowpass filter to the N-S geophone:
http://voksenlia.net/nytt/2011/jordskjelv-20110311.jpg
And here's the raw unfiltered seismometer plot:
http://voksenlia.net/nytt/2011/jordskjelv-20110311b.jpg
It's badly clipped, so it's less useful to study.
=20
i Steinar,  =20
    I suggest that you check the gain setting on=20
your SEPUK. You have a choice of SWITCHED gains of=20
x100, x200 and x500. If your signal is going off=20
scale, can you not switch to a lower gain? The manual=20
(which is worth reading for others using or constructing=20
Lehmans) is on line at=20
www.mutr.co.uk/images/seismometer.pdf
    I bought a x10 period extension board for my 4.5 Hz=20
geophones from www.sara.pg.it It works very well and it=20
effectively gives me 3 off 0.5 Hz geophones! These are
well matched for all P and S waves.
    Regards,
    Chris Chapman















=
From: Steinar Midtskogen steinar@l=
atinitas.org

Subject: Re: Lehman seismometer movement





By ext=
rapolating http://jclahr.com/science/psn/magnitude.html we
should expect about 2 cm (!) ground movement at this distance, but I
expect that this would be longer periods than what my Lehman was
designed for.

While my observation might be plausible I'm actually more impressed
with what I saw on my 4.5 Hz geophones.  Here's what I get if I apply
a 1 Hz lowpass filter to the N-S geophone:

http://voksenlia.net/nytt/2011/jordskjelv-20110311.jpg

And here's the raw unfiltered seismometer plot:

http://voksenlia.net/nytt/2011/jordskjelv-20110311b.jpg

It's badly clipped, so it's less useful to study.

=20
Hi Steinar,   
your SEPUK. Y=
ou have a choice of SWITCHED gains of 
x100, x200 and x500. If your signal is going =
off 
scal=
e, can you not switch to a lower gain? The manual 
(which is worth reading for other=
s using or constructing 
Lehmans) is on line at 
www.mutr.co.uk/images/seismometer.pdf=
    I bought a x10 p=
eriod extension board for my 4.5 Hz 
geophones from <=
A href=3D"http://www.sara.pg.it">www.sara.pg.it It works very well and =
it 
effec=
tively gives me 3 off 0.5 Hz geophones! These are
well matched for all P and S waves=
..
    Reg=
ards,
   =
 Chris Chapman