In a message dated 17/03/2006, jonfr500@......... writes:

With a  long period seismometer what is the smallest earthquake that can  be
detected with such a seismometer? I mean in the teleseismic earthquake  range.



Hi Jon,
 
    It depends on your instrument characteristics, the  intrinsic equipment 
noise and on the local ambient seismic noise levels.  For a system using 4.5 Hz 
geophones without period extension, you are  likely to be frequency limited 
to local and near regional quakes, less than 6  deg, maybe quite a lot less. If 
you can detect 1.0, 0.5 Hz and longer period  events either with different 
instruments or with low frequency period extension,  you should be able to 
detect M6 quakes worldwide, but how much smaller will  depend on the range of the 
quake and on your local noise, which is weather,  environment and time related.
 
    Some data for an AS-1 can be found at 
_http://www2.bc.edu/~kafka/SeismoEd_SRL/kr03_page1.html_ (http://www2.bc.edu/~kafka/SeismoEd_SRL/kr03_page1.html) 
   See page 6. I would expect a good quality Lehman or SG seismometer with a 
period  of 20 sec to do better than this - the long period waves are of 
greater  amplitude and the noise is likely to be less. Regional quakes are defined 
as  being from 6 to 16 deg and teleseismic from 16 to 180 deg. There are 
several  regions in the teleseismic range which have different characteristic and 
many  different paths possible
 
    Regards,
 
    Chris Chapman






In a message dated 17/03/2006, jonfr500@......... writes:
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Hi Jon,
 
    It depends on your instrument characteristics,=20=
the=20
intrinsic equipment noise and on the local ambient seismic noise levels=
..=20
For a system using 4.5 Hz geophones without period extension, you are=20
likely to be frequency limited to local and near regional quakes, less than=20=
6=20
deg, maybe quite a lot less. If you can detect 1.0, 0.5 Hz and longer period=
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events either with different instruments or with low frequency period extens=
ion,=20
you should be able to detect M6 quakes worldwide, but how much smaller will=20
depend on the range of the quake and on your local noise, which is weather,=20
environment and time related.
 
    Some data for an AS-1 can be found at http://www2.=
bc.edu/~kafka/SeismoEd_SRL/kr03_page1.html =20
See page 6. I would expect a good quality Lehman or SG seismometer with a pe=
riod=20
of 20 sec to do better than this - the long period waves are of greater=20
amplitude and the noise is likely to be less. Regional quakes are defined as=
=20
being from 6 to 16 deg and teleseismic from 16 to 180 deg. There are several=
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regions in the teleseismic range which have different characteristic and man=
y=20
different paths possible
 
    Regards,
 
    Chris Chapman