Subject: RE: Lehman seismometer movement


Chris,
our analysis seems a bit pessimistic.  There's no need to settle=20
or a 50 cm arm - for a mirror on a separate suspension coupled to=20
he proof mass 1 cm would seem achievable, which, combined with a
0 m long arm gives a gain of 1000 without multiple mirror trips. =20
he information I have says that the surface waves for a magnitude=20
 quake at 60 degrees have ground displacements of 10 microns. =20
his would give a beam displacement of 1 cm; hardly tiny.
Cheers,
ack
Hi Jack,
    Sure, but you can't make a long period seismometer this way!!=20
The early Wood-Andersen torsion seismometer was made like this, but
it had a period of about 1/2 second, if I remember correctly. It=20
did not pick up 20 second surface waves at all well (over 1000 down),=20
only the P and S waves.
    Regards,

    Chris Chapman





=
Subject: RE: Lehman seismometer movement





Chris,
Your analysis seems a bit pessimistic.  There's no need to settle=20
for a 50 cm arm - for a mirror on a separate suspension coupled to=20
the proof mass 1 cm would seem achievable, which, combined with a
10 m long arm gives a gain of 1000 without multiple mirror trips. =20
The information I have says that the surface waves for a magnitude=20
6 quake at 60 degrees have ground displacements of 10 microns. =20
This would give a beam displacement of 1 cm; hardly tiny.

Cheers,
Jack

Hi Jack,
=
    Sure, but you can't make a long period seismometer this =
way!! 
Th=
e early Wood-Andersen torsion seismometer was made like this, but
it had a period of=
 about 1/2 second, if I remember correctly. It 
did not pick up 20 second surface wa=
ves at all well (over 1000 down), 
only the P and S w=
aves.

    Regards,
 
    Chris Chapman