Jerry -

They do not give a reason for that particular bit of research.  It  
would interesting to know what the project was.  As you previously  
said, seismometers are normally orientated, vertical, north/south and  
east/west.

S waves are transverse waves which oscillate 90 degrees to the ray  
path.  There are two components to a S wave, SH (S wave horizontal  
component), and SV (S wave vertical component).

When seismologists view a seismogram, they usually rotate the data  
first, so instead of looking at ZNE data, they add two additional  
channels, for the following ZNERT.  The R stands for radial and T  
stands for transverse.  There is a option in the SAC program which  
allow you to align the two horizontal channels mathematically with the  
radial and transverse components,  Check page 57, right side column  
for the two complete paragraphs.  I have copied the two paragraphs  
below for the benefit of those who do not have access to the book.

"...In real applications, we often define the z axis as the vertical  
direction and orient the x-z plane along the great circle connecting a  
seismic source and a receiver.   Plane waves traveling on the direct  
path between the source and the receiver thus propagate in the x-z  
plane.  The shear wave polarization directions are defined as SV, for  
shear waves with displacement in the vertical (x-z) plane, and SH, for  
horizontally polarized shear waves with displacement in the y  
direction, parallel to the earth's surface.  Both have displacements  
perpendicular to the propagation direction and the other polarization  
(Fig. 2.4-4, overleaf).  Although we could choose any two orthogonal  
polarizations in the plane of the shear wave displacements, using SV  
and SH is particularly convenient.  We will see that P and SV waves  
are coupled with each other when they interact with horizontal  
boundaries, whereas SH waves remain separate.

Seismometers record horizontal motions in the north-south and east- 
west directions, which rarely correspond exactly to the SH and SV  
polarizations.  As a result, data from the horizontal components of  
seismometers are often rotated.  The direction connecting the source  
and the receiver, corresponding to SV displacements, is called the  
radial direction, so a seismogram rotated to this direction is called  
the radial component.  Similarly, the orthogonal direction  
corresponding to SH displacements is called transverse direction, so a  
seismogram rotated to this direction is called the transverse  
component...."

Following is a mathematical explanation of rotation from Professor  
George Zandt, University of Arizona:

"...Rotation, or more precisely, rotation of seismograms from the ZNE  
coordinates to ZRT coordinates is relatively straightforward. The  
choice of recording the NS and EW components of ground motion is  
rather arbitrary, right? You just need to record two orthogonal (at rt  
angles) directions, could be NE and SE, but by convention  
sesimologists always use N and E. If your events are coming from N or  
S or E or W, then the data is called "naturally rotated" and you can  
clearly see the separation of Love and Rayleigh, for example. But for  
any other direction, its not naturally rotated. So, you can rotate the  
data yourself to the radial and transverse directions. Mathematically,  
this is quite simple and involves multiplying the data by cosine of  
the difference in angles. There is a command in SAC that does this...."

Hope this helps you a little.

Bob Hancock





On Sep 27, 2009, at 12:11 PM, GPayton wrote:

> Page 3 of  Introduction, left column at bottom.  Referencing Figure  
> 1.1-4.....
>
> Jerry
>
>
> ----- Original Message ----- From: "Bob Hancock" 
> To: 
> Sent: Sunday, September 27, 2009 2:02 PM
> Subject: Re: Seismometer Siting
>
>
>> Jerry -
>>
>> I have the book - what page and where on the page did you read this.
>>
>> Bob Hancock
>>
>>
>> On Sep 27, 2009, at 11:14 AM, GPayton wrote:
>>
>>> 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.
>>>
>>> Thanks,.
>>> Jerry Payton
>>
>> __________________________________________________________
>>
>> Public Seismic Network Mailing List (PSN-L)
>>
>> To leave this list email PSN-L-REQUEST@.............. with the body  
>> of the message (first line only): unsubscribe
>> See http://www.seismicnet.com/maillist.html for more information.
>
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with the body  
> of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
>


Seismometers record horizontal =
motions in the north-south and east-west directions, which rarely =
correspond exactly to the SH and SV polarizations.  As a result, =
data from the horizontal components of seismometers are often rotated.  The =
direction connecting the source and the receiver, corresponding to SV =
displacements, is called the radial direction, so a seismogram rotated to =
this direction is called the radial component.  Similarly, the =
orthogonal direction corresponding to SH displacements is called transverse direction, so =
a seismogram rotated to this direction is called the transverse =
component...."

Following is a mathematical =
explanation of rotation from Professor George Zandt, University of =
Arizona:

"...Rotation, or more precisely, =
rotation of seismograms from the ZNE coordinates to ZRT coordinates is =
relatively straightforward. The choice of recording the NS and EW =
components of ground motion is rather arbitrary, right? You just need to =
record two orthogonal (at rt angles) directions, could be NE and SE, but =
by convention sesimologists always use N and E. If your events are =
coming from N or S or E or W, then the data is called "naturally =
rotated" and you can clearly see the separation of Love and Rayleigh, =
for example. But for any other direction, its not naturally rotated. So, =
you can rotate the data yourself to the radial and transverse =
directions. Mathematically, this is quite simple and involves =
multiplying the data by cosine of the difference in angles. There is a =
command in SAC that does this...."

Hope this =
helps you a little.

Bob =
Hancock




<=
br>
On Sep 27, 2009, at 12:11 PM, GPayton wrote:

Page =
3 of  Introduction, left column at bottom.  Referencing Figure =
1.1-4.....

Jerry


----- Original Message ----- From: =
"Bob Hancock" <icarus@.........>
To: <psn-l@..............>
Sent:=
 Sunday, September 27, 2009 2:02 PM
Subject: Re: Seismometer =
Siting


Jerry =
-

I have the book - what page and where on the page did you =
read this.

Bob =
Hancock


On Sep 27, =
2009, at 11:14 AM, GPayton wrote:

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.

Thanks,.
Jerry =
Payton

__________________________________________________________

Public Seismic Network Mailing List =
(PSN-L)

To leave this =
list email PSN-L-REQUEST@..............<=
/a> with the body of the message (first line only): =
unsubscribe
See http://www.seismicnet.com=
/maillist.html for more =
information.


_____________________________________=
_____________________

Public Seismic Network Mailing List =
(PSN-L)

To leave this list email PSN-L-REQUEST@..............<=
/a> with the body of the message (first line only): unsubscribe
See =
http://www.seismicnet.com=
/maillist.html for more =
information.


=