In a message dated 21/12/02, hammond@........... writes:

> Chris, with regard to your comments on vertical seismometers, I invite you 
> to visit my web page http://apsn.awcable.com  and specifically look at 
> "earthquakes recorded at station GSV". Every earthquake I record and 
> display 
> is using a Mark Products L4 1Hz short-period vertical seismometer. Surely, 
> you  must be joking that short period vertical seismometers are of limited 
> use!

Hi Bob, 

       You make my point very well! Unless you have done some modifications, 
the L4 is a commercial 1 Hz geophone. It is a sealed unit and so is immune to 
atmospheric pressure changes. It is fully magnetically screened and uses a 
professional standard suspension. It also costs over $1 K new. I note that 
the majority of the quakes are 'local'. If you care to extend it's range down 
to 0.1 Hz electronically, you will get improved detection of lower frequency 
P and S tele seismic waves.

       Now, if you could actually demonstrate a simple 1 to 2 second period 
vertical seismometer of comparable quality which can easily be made by an 
amateur, I am sure that it would generate a whole lot of interest. I am not 
joking about the utility, or otherwise, of the current construction designs 
that I have seen on offer.

       Regards,

       Chris Chapman
In a message dated 21/12/02, hammond@........... writes:



Chris, with regard to your comments on vertical seismometers, I invite you 

to visit my web page http://apsn.awcable.com  and specifically look at "earthquakes recorded at station GSV". Every earthquake I record and display 

is using a Mark Products L4 1Hz short-period vertical seismometer. Surely, you  must be joking that short period vertical seismometers are of limited use!




Hi Bob, 



       You make my point very well! Unless you have done some modifications, the L4 is a commercial 1 Hz geophone. It is a sealed unit and so is immune to atmospheric pressure changes. It is fully magnetically screened and uses a professional standard suspension. It also costs over $1 K new. I note that the majority of the quakes are 'local'. If you care to extend it's range down to 0.1 Hz electronically, you will get improved detection of lower frequency P and S tele seismic waves.



       Now, if you could actually demonstrate a simple 1 to 2 second period vertical seismometer of comparable quality which can easily be made by an amateur, I am sure that it would generate a whole lot of interest. I am not joking about the utility, or otherwise, of the current construction designs that I have seen on offer.



       Regards,



       Chris Chapman