In a message dated 28/05/2009, system98765@............. writes:

Since  Rayleigh waves are vertical but vertical geophones are more designed
for  vertical, higher frequency motions, would the geophone still pick up
these  Rayleigh waves very well?
Hi Gary,
 
    This depends on the resonant frequency of your  geophone, the frequency 
of the wave and the amplifier characteristics. A 1  Hz wave on a 4.5 Hz 
geophone will be (1/4.5)^2 down in amplitude = 1/20.25. 
    A 20 second wave will be (1/20*4.5)^2 down in  amplitude = 1/8,100 so 
the waves would have to be huge to show up at all. 
    If you added a period compensating amplifier from  4.5 to 0.5 Hz, the 
20 second wave would be 1/100 down in amplitude, so you  might well see it. A 
1 Hz wave would be at full amplitude.

Also, in  regard to the 20 second statement, does this mean that twenty
seconds pass  before the second wave crest passes the sensor's location? 
    Correct.

What  does that look like on the seismogram? Seems like the record wouldn't 
display  much of a dramatic signature would it? Or would it display smooth 
wavy  lines?
    It usually looks like a fairly smooth wave 3 times  each minute, but 
you also get interference effects / humps /  beats and  noise.
 
    Regards,
 
    Chris Chapman









In a message dated 28/05/2009, system98765@............. writes:
Since 
  Rayleigh waves are vertical but vertical geophones are more designed
=
for 
  vertical, higher frequency motions, would the geophone still pick up
=
these 
  Rayleigh waves very well?
Hi Gary,
 
    This depends on the resonant frequency of you=
r 
geophone, the frequency of the wave and the amplifier characteristics=
.. A 1 
Hz wave on a 4.5 Hz geophone will be (1/4.5)^2 down in amplitude =3D 1/20.=
25. 

    A 20 second wave will be (1/20*4.5)^2 down in=
 
amplitude =3D 1/8,100 so the waves would have to be huge to show up at all=
.. 
    If you added a period compensating amplifier=
 from 
4.5 to 0.5 Hz, the 20 second wave would be 1/100 down in amplitude,=
 so you 
might well see it. A 1 Hz wave would be at full amplitude.
Also, in 
  regard to the 20 second statement, does this mean that twenty
seconds=
 pass 
  before the second wave crest passes the sensor's location? 
    Correct.
What 
  does that look like on the seismogram? Seems like the record wouldn't di=
splay 
  much of a dramatic signature would it? Or would it display smooth wavy=
 
  lines?
    It usually looks like a fairly smooth wave 3=
 times 
each minute, but you also get interference effects / humps /  beats=
 and 
noise.
 
    Regards,
 
    Chris Chapman