In a message dated 30/09/01, rlthompson@................. writes:

>     Late one recent night I realized that building a seismic detector for my 
> location may be a waste of time.
>     The airport is realitively close to the town, and that night the 
> departing aircraft were flying over the town. Some of the larger aircraft 
> rattle the windows, and shake the house. Is this type of vibration likely 
> to be detected on a seismograph?    

       Depends a bit where you put your seismometer and what frequencies / 
periods you use. Environmental noise tends to be bad from maybe 20 Hz up, but 
this should have been filtered out anyway.      

       The top cut seis filter is maybe 10 Hz for quieter locations, or 3 Hz 
for noisier ones. You get the ocean background between 1 and 10 seconds, 
maybe peaking in the 6 second region, so if you are looking at 3 Hz down to 1 
Hz or below 0.1 Hz, you will probably be OK. 

       You must not expect the earth to be 'quiet' anyway. Sorting out which 
signal is due to which cause is all part of the fun. I have a gale blowing 
here at the moment and the background noise is way up. Can't even pick out 
the traffic from the main road about 100 yards away, which more usually gives 
me problems! With viewing programmes like Winquake, you can do digital 
filtering and remove a lot of noise after it has been recorded. The results 
can be quite spectacular.

       Have you made any progress with the sensor electronics that you were 
going to try out, yet? Do keep us informed!

       Regards,

       Chris Chapman

In a message dated 30/09/01, rlthompson@................. writes:



  
;  Late one recent night I realized that building a seismic detector for my location may be a waste of time.

    The airport is realitively close to the town, and that night the departing aircraft were flying over the
 town. Some of the larger aircraft rattle the windows, and shake the house. Is this type of vibration likely to be detected on 
a seismograph?    



       Depends a bit where you put your seismometer and what frequencies / periods you use. E
nvironmental noise tends to be bad from maybe 20 Hz up, but this should have been filtered out anyway.     
 



       The top cut seis filter is maybe 10 Hz for quieter locations, or 3 Hz for noisier ones
. You get the ocean background between 1 and 10 seconds, maybe peaking in the 6 second region, so if you are looking at 3 Hz do
wn to 1 Hz or below 0.1 Hz, you will probably be OK. 



       You must not expect the earth to be 'quiet' anyway. Sorting out which signal is due to
 which cause is all part of the fun. I have a gale blowing here at the moment and the background noise is way up. Can't even pi
ck out the traffic from the main road about 100 yards away, which more usually gives me problems! With viewing programmes like 
Winquake, you can do digital filtering and remove a lot of noise after it has been recorded. The results can be quite spectacul
ar.



       Have you made any progress with the sensor electronics that you were going to try out,
 yet? Do keep us informed!



       Regards,



       Chris Chapman