## PSN-L Email List Message

Subject: Re: Honduras Quake 5/28/09
From: ChrisAtUpw@.......
Date: Thu, 28 May 2009 18:21:00 EDT

```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 twentyseconds=
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

```