Thanks for this information.   Chris, These are  amateur sensors, and =
students.   Ted
  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Monday, October 23, 2006 9:56 AM
  Subject: Re: Local vs distance events


  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,=20

         ?????

         Are these amateur or professional sensors?

         There are a variety of sensors available professionally.=20
         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,








Thanks for this =
information.  =20
Chris, These are  amateur sensors, and students.  =20
Ted

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Monday, October 23, 2006 =
9:56=20
  AM
  
Subject: Re: Local vs distance=20
  events
  

In a=20
  message dated 2006/10/23, tchannel@..............=20
  writes:


  Hi,  I was asked to explain the different between =
Sensors=20
    developed for local events vs those developed for long distance=20
    events.
Is there a summary posted that explains this in =
terms easy to=20
    understand? This is for a group of children and =
adults.

Hi=20
  Ted, 

      =20
  ?????

       Are these amateur or =

  professional sensors?

       =
There are a=20
  variety of sensors available professionally.=20
  
       4.5 Hz and more particularly =
1 Hz=20
  geophones may be used for local quakes / volcanoes and may record from =
60 Hz=20
  down to the corner frequency.
       =
Then you=20
  have a variety of broad band medium to high sensitivity seismic =
sensors which=20
  record from 50 / 40 Hz all the way to 40, 60, 120 or even 360=20
  seconds.
       Then there are =
'strong=20
  motion' sensors, more often used close to faults or for civil =
engineering.=20
  These record accelerations up to about 2 g but may only go down to a =
milli g=20
  and are usually broad =
band.

       Local=20
  events may have motion components from maybe 40 Hz down to 30=20
  seconds.

       As quake waves =
travel=20
  through / over the surface of the Earth, the higher frequencies are=20
  selectively absorbed.

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

      =20
  Regards,

       Chris =
Chapman=20