In a message dated 28/12/2009, gmvoeth@........... writes:

Below  resonance at 1Hz for a SPZ Velocity device
I recommend no more than 6dBv  per octave (20 per decade)
because if you go 40 you get terrible  microseismic interferences.



Hi Geoff,
 
    I don't understand the rest of your Email.
 
    Normal coil + magnet devices all give a roll off at  40 dB per decade, 
which needs to be compensated if you want to detect longer  period seismic 
signals. YOU DON'T HAVE ANY CHOICE! 
 
    However, you can extend the period of a geophone or  an AS1 type 
vertical sensor by x10 without running into noise problems. So  a seismometer with 
a natural period of 1.5 seconds can fairly easily be  extended to 20 
seconds. This enables it to cover most of the 'normal'  seismic band quite OK for 
amateur purposes.
 
    I use this system and it works. I simply  filter out the microseisms on 
the drumplot display in Amaseis, but they are  normal in size as on a 
broadband sensor.
 
    Regards,
 
    Chris Chapman
 
 






In a message dated 28/12/2009, gmvoeth@........... writes:
Below=20
  resonance at 1Hz for a SPZ Velocity device
I recommend no more than=
 6dBv=20
  per octave (20 per decade)
because if you go 40 you get terrible=20
  microseismic interferences.


Hi Geoff,
 
    I don't understand the rest of your Email.
 
    Normal coil + magnet devices all give a roll=
 off at=20
40 dB per decade, which needs to be compensated if you want to detect long=
er=20
period seismic signals. YOU DON'T HAVE ANY CHOICE! 
 
    However, you can extend the period of a geoph=
one or=20
an AS1 type vertical sensor by x10 without running into noise problems. So=
=20
a seismometer with a natural period of 1.5 seconds can fairly easily=
 be=20
extended to 20 seconds. This enables it to cover most of the 'normal'=
=20
seismic band quite OK for amateur purposes.
 
    I use this system and it works. I simply=
=20
filter out the microseisms on the drumplot display in Amaseis, but they ar=
e=20
normal in size as on a broadband sensor.
 
    Regards,
 
    Chris Chapman