In a message dated 2006/10/23, tchannel@.............. writes:

> Hi,  I was asked to explain the different between Sensors developed for 
> local events vs those developed for long distance events.
> Is there a summary posted that explains this in terms easy to understand? 
> This is for a group of children and adults.

Hi Ted, 

       ?????

       Are these amateur or professional sensors?

       There are a variety of sensors available professionally. 
       4.5 Hz and more particularly 1 Hz geophones may be used for local 
quakes / volcanoes and may record from 60 Hz down to the corner frequency.
       Then you have a variety of broad band medium to high sensitivity 
seismic sensors which record from 50 / 40 Hz all the way to 40, 60, 120 or even 360 
seconds.
       Then there are 'strong motion' sensors, more often used close to 
faults or for civil engineering. These record accelerations up to about 2 g but may 
only go down to a milli g and are usually broad band.

       Local events may have motion components from maybe 40 Hz down to 30 
seconds.

       As quake waves travel through / over the surface of the Earth, the 
higher frequencies are selectively absorbed.

       Teleseismic quakes tend to have P waves of 1 to 2 Hz, S waves about 
0.45 the frequency of the P waves and Love / Rayleigh long surface waves with 
periods less than 60 seconds, often about 15 to 30 seconds. However, those from 
'great' quakes may have waves of much greater periods.

       Regards,

       Chris Chapman
In a me=
ssage dated 2006/10/23, tchannel@.............. writes:



Hi,  I was asked to explai=
n the different between Sensors developed for local events vs those develope=
d for long distance events.

Is there a summary posted that explains this in terms easy to understand? T=
his is for a group of children and adults.




Hi Ted, 



       ?????



       Are these amateur or professional senso=
rs?



       There are a variety of sensors availabl=
e professionally. 

       4.5 Hz and more particularly 1 Hz geoph=
ones may be used for local quakes / volcanoes and may record from 60 Hz down=
 to the corner frequency.

       Then you have a variety of broad band m=
edium to high sensitivity seismic sensors which record from 50 / 40 Hz all t=
he way to 40, 60, 120 or even 360 seconds.

       Then there are 'strong motion' sensors,=
 more often used close to faults or for civil engineering. These record acce=
lerations up to about 2 g but may only go down to a milli g and are usually=20=
broad band.



       Local events may have motion components=
 from maybe 40 Hz down to 30 seconds.



       As quake waves travel through / over th=
e surface of the Earth, the higher frequencies are selectively absorbed.



       Teleseismic quakes tend to have P waves=
 of 1 to 2 Hz, S waves about 0.45 the frequency of the P waves and Love / Ra=
yleigh long surface waves with periods less than 60 seconds, often about 15=20=
to 30 seconds. However, those from 'great' quakes may have waves of much gre=
ater periods.



       Regards,



       Chris Chapman