PSN-L Email List Message
Subject: Re: Seismometer Siting
From: Brett Nordgren brett3nt@.............
Date: Mon, 28 Sep 2009 11:21:41 -0400
It relates to the direction of the ground oscillations caused by different
phases. P waves, more or less, vibrate at right angles to S waves. So,
*for a particular quake*, if you point your sensor in the direction of the
arriving P waves in order to see them the best, you would then have to turn
it by 90 degrees to pick up the S waves most strongly, something like
aiming a directional radio antenna.
With two or three-axis sensors the pointing can be done mathematically with
a computer, working on the saved data, rather than by actually rotating the
sensor, which allows you to easily estimate the direction of the source of
At 07:37 AM 9/28/2009 -0700, you wrote:
>It seems silly to me that you can differentiate between
>various types of disturbances in any way except through
>frequencies. Even P waves can present themselves
>with motion or deformation in almost any direction.
>We live at a phase boundary between air and earth
>where waves will meet a melodramatic velocity change.
>Where P can become S and vice versa.
>----- Original Message ----- From: "GPayton"
>To: "PSN Network List"
>Sent: Sunday, September 27, 2009 11:14 AM
>Subject: Seismometer Siting
>>Over and over, I have read that normally a seismometer is sited for N-S,
>>E-W, and Vertical sensing.
>>However, I just read a paragraph in An Introduction to Seismology,
>>Earthquakes and Earth Structure about a seismometer in Hawaii that "was
>>oriented to receive S phase signals." How is that accomplished?
>>I could venture a guess, but probably would be wrong.
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