In a message dated 2007/06/30, tchannel1@............ writes:

> Hi All,  I just did a side by side comparison of an Earthquake recorded by 
> a Vertical with a 2? second period and a Horz Pendulum with a 10? second 
> period.  The different on this 6.7M at 10000km was very pronounced, showing all 
> the advantages of the Horz.
>  
> However, using the Vertical, I record many more Earthquake, and smaller 
> ones.  If the event is large, both sensors are impressive (to me).
>  
> In planning my next sensor, I need to pick a target period. I already see 
> the advantage of each.  What period might be the best target?  Or is it just 
> better to pick one end of the spectrum and not the center?

Hi Ted,

       The 'old type' seismic systems used short and long period sensors to 
avoid the ocean background signals between 4 and 10 seconds. With computer data 
capture and analysis, this is no longer necessary, but you may choose to use 
a twin Tee reject filter operating at about 6 seconds. 
       The P waves tend to roll in from 0.5 to 10 Hz, with frequencies over 
3.3 Hz associated with quakes less than 1000 km away. You often look for P 
waves from 1 to 3 Hz.
       The S waves roll in at 0.2 to 10 Hz, with frequencies over 2 Hz 
assocoiated with quakes less than 1000 km away. The frequency is slightly more than 
half the associated P wave.
       The Love and Rayleigh waves may have periods from 2 to 500 sec, but 
many have periods ~20 seconds, occasionally over 40 seconds.
       It is fairly easy to makea vertical sensor with a period of 0.5 to 
0.67 Hz and above. This can be extended to 1/10 th electronically.
       Lehman horizontal types are fairly easy to make out to 20 to 30 
seconds. Above this they tend to be very sensitive to ground tilt changes / 
instability. Adding feedback can help a lot.

       Regards,

       Chris Chapman   
In a me=
ssage dated 2007/06/30, tchannel1@............ writes:



Hi All,  I just did a side=
 by side comparison of an Earthquake recorded by a Vertical with a 2? second=
 period and a Horz Pendulum with a 10? second period.  The different on=
 this 6.7M at 10000km was very pronounced, showing all the advantages of the=
 Horz.

 

However, using the Vertical, I record many more Earthquake, and smaller one=
s.  If the event is large, both sensors are impressive (to me).<=
FONT  COLOR=3D"#000000" BACK=3D"#ffffff" style=3D"BACKGROUND-COLOR: #ffffff"=
 SIZE=3D3 PTSIZE=3D12 FAMILY=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"0">

 

In planning my next sensor, I need to pick a target period. I already see t=
he advantage of each.  What period might be the best target?  Or i=
s it just better to pick one end of the spectrum and not the center?<=
FONT  COLOR=3D"#000000" BACK=3D"#ffffff" style=3D"BACKGROUND-COLOR: #ffffff"=
 SIZE=3D3 PTSIZE=3D12 FAMILY=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"0">



Hi Ted,



       The 'old type' seismic systems used sho=
rt and long period sensors to avoid the ocean background signals between 4 a=
nd 10 seconds. With computer data capture and analysis, this is no longer ne=
cessary, but you may choose to use a twin Tee reject filter operating at abo=
ut 6 seconds. 

       The P waves tend to roll in from 0.5 to=
 10 Hz, with frequencies over 3.3 Hz associated with quakes less than 1000 k=
m away. You often look for P waves from 1 to 3 Hz.

       The S waves roll in at 0.2 to 10 Hz, wi=
th frequencies over 2 Hz assocoiated with quakes less than 1000 km away. The=
 frequency is slightly more than half the associated P wave.

       The Love and Rayleigh waves may have pe=
riods from 2 to 500 sec, but many have periods ~20 seconds, occasionally ove=
r 40 seconds.

       It is fairly easy to makea vertical sen=
sor with a period of 0.5 to 0.67 Hz and above. This can be extended to 1/10=20=
th electronically.

       Lehman horizontal types are fairly easy=
 to make out to 20 to 30 seconds. Above this they tend to be very sensitive=20=
to ground tilt changes / instability. Adding feedback can help a lot.



       Regards,



       Chris Chapman