In a message dated 30/12/2005, jonfr500@......... writes:

> I am wondering about harmonic tremors and a 4,5Hz geophone that I have.
> I know from a data that is on the internet, that harmonic tremors can be
> on 5 - 6Hz or lower and higer (it depends on many factors).

Hi Jon,

       Can you give me a reference / source / website for what you are 
calling 'harmonic tremors', please? The name does not mean anything to me.

       There are the universal ocean background signals, or microseisms, 
lying in the period range of 4 to 9 seconds, more usually about 6 seconds = 0.17 
Hz, NOT 6 Hz. The amplitude may be from 0.5 micron to over 15 microns in storm 
conditions. You probably won't pick this up on your 4.5 Hz geophone, unless 
there is a severe storm locally. If you live near the sea, you may also observe 
waves breaking on the shore.

       The other regular tremors which can bother seismologists over a wide 
range of frequencies, are caused by wind noise. These can be from the several 
hundred Hz singing noise of telephone wires down to many 10s of seconds 
produced by whole mountains. The frequency is directly proportional to the local wind 
speed and inversely proportional to the cross wind dimension (width) of the 
object, tree, building, etc. producing it. You can expect to feel the effects 
for over 100x the dimension of the object in a downwind direction. Tall 
buildings and trees will radiate vibrations locally through the ground. If you have 
ever driven a motorcycle fairly closely behind a high lorry, you may have 
noticed the alternate left and right gusts typical of these Von Karman vortices.

       Regards,

       Chris Chapman
In a message dated 30/12/2005, jonf=
r500@......... writes:



I am wondering about harmonic t=
remors and a 4,5Hz geophone that I have.

I know from a data that is on the internet, that harmonic tremors can be

on 5 - 6Hz or lower and higer (it depends on many factors).




Hi Jon,



       Can you give me a reference / source /=20=
website for what you are calling 'harmonic tremors', please? The name does n=
ot mean anything to me.



       There are the universal ocean backgroun=
d signals, or microseisms, lying in the period range of 4 to 9 seconds, more=
 usually about 6 seconds =3D 0.17 Hz, NOT 6 Hz. The amplitude may be=20=
from 0.5 micron to over 15 microns in storm conditions. You probably won't p=
ick this up on your 4.5 Hz geophone, unless there is a severe storm locally.=
 If you live near the sea, you may also observe waves breaking on the shore.=




       The other regular tremors which can bot=
her seismologists over a wide range of frequencies, are caused by wind noise=
.. These can be from the several hundred Hz singing noise of telephone wires=20=
down to many 10s of seconds produced by whole mountains. The frequency is di=
rectly proportional to the local wind speed and inversely proportional to th=
e cross wind dimension (width) of the object, tree, building, etc. producing=
 it. You can expect to feel the effects for over 100x the dimension of the o=
bject in a downwind direction. Tall buildings and trees will radiate vibrati=
ons locally through the ground. If you have ever driven a motorcycle fairly=20=
closely behind a high lorry, you may have noticed the alternate left and rig=
ht gusts typical of these Von Karman vortices.



       Regards,



       Chris Chapman