Hi Ian,

There are three types of earthquakes. Normal high frequancy events that
happen when the crust breaks. We usally get those all the time. Then
there are the volcano type of earthquakes, that happen just before a
volcano starts a eruption, here is a good sample of such earthquake that
I did record last weekend. This trance is filtered at 2Hz,
http://seismicnet.com/cgi-dos/makegif.exe?/quakes/1002/100220.180800.hkbe.p=
sn
http://seismicnet.com/cgi-dos/makegif.exe?/quakes/1002/100220.180800.hkbn.p=
sn
http://seismicnet.com/cgi-dos/makegif.exe?/quakes/1002/100220.180800.hkbz.p=
sn

Then there is the harmonic tremor that can be seen when magma is pushing
up trugh the crust in a eruption. I have never seen those, but those how
are living near a activie volcano that is erupting should see all the
time. I don't know how well 4.5Hz geophone can pickup such tremors. But
I do know that I am going to get a answer to that question soon.

http://en.wikipedia.org/wiki/Harmonic_tremor
http://earthquake.usgs.gov/learn/glossary/?term=3Dharmonic%20tremor

Regards,
J=F3n Fr=EDmann.

On =FEri, 2010-02-23 at 19:56 +0000, ian wrote:
> Hi,
>=20
> I'm not sure what the answer is but I posted a few local volcano=20
> tremours to psn in 2001.  For instance, see=20
> http://www.webtronics.com/cgi-dos/makegif.exe?/quakes/0105/010512a.hl1.ps=
n=20
> and the data file is at=20
> http://www.webtronics.com/quakes/0105/010512a.hl1.psn
>=20
> You can also search the records for 2001 with station id hl1.  I found 4=20
> this way.  I suspect I posted more but perhaps the search function isn't=20
> perfect.  Tony at Quakekona posted much more and was way better than I wa=
s.
>=20
> Cheers
>=20
> Ian
>=20
>=20
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