Thread: problems rotating components and removing instrument response

Started: 2019-05-21 16:26:00
Last activity: 2019-05-21 22:57:37
Topics: SAC Help
Dear,

I have downloaded data from many events. I need to rotate and remove
instrument response of all of them. I am using sac.

1) Some of the events have the components called BH1 and BH2 (or BH2 and
BH3) instead of BHE and BHN. To rotate, I need to know which one is BHE and
which one BHN. For that, I watched the header information looking for
CMPAZ=90 - CMPINC=90 for East component BHE, and CMPAZ=0 - CMPINC=90 for
North component BHN.
The problem was that in some cases the numbers of the CMPAZ were not the
expected ones.
Here I show you just two examples,
Network Station Event BH1 (AZ—INC) BH2 (AZ—INC)
2A 42 2002-11-15-mw66-south-georgia-island-region 0 – 90 0 – 90
IU DWPF 2012-04-14-mw62-drake-passage 311 – 90 41 – 90

2) Another problem appeared when the components BHE and BHN were not an
orthogonal pair so I could not rotate. What shall I do in those cases? Can
I just modify the CMPAZ value to make the pair orthogonal? Or I should look
a solution in another way?
For example:
Network Station Event BHE (AZ) BHN (AZ)
II ASCN 2004-12-22-mw60-southern-east-pacific-rise 93 2
II SUR 2007-11-29-mw63-west-chile-rise 87,4 358,6

3) I had a third problem when I tried to remove the instrument response on
events occurred on 2012 and recorded by the TROLL station (NO network). The
next error message appeared: "*ERROR 2118: No transfer function applied.
Unrecognized Constant: 0.000000 e+00*". I did not know how to fix this.

I have already written to Data Processing Help list, but they told me to
write this list.
I wish you could help me. Thank you in advance.
Kind regards,


Geof. Duca Freyre, Leticia
Dpto. de Sismología e Inf. Meteorológica
Facultad de Ciencias Astronómicas y Geofísicas
Universidad Nacional de La Plata
Tel: (+54) 221 4236593, int: 1155

  • Hola Leticia,

    I think Gabriela Badi can help you with these topics..anyway

    1) Channels denominates BHN and BHE are oriented justly in geographic North and East, so have AZ=0 for North and AZ=90 for East component,
    When use BH1 And BH2, means AZ take some value different from 0 for N and different of 90 for E, but must to maintain the orthogonality in both cases.
    INC is always 90 for horizontals components, for sign see the conventions for SAC and SEED format.

    2) BHN and BHE have a small difference, rotate to N (from 2 to 0) or E (from 93 to 90) these small angles shouldn’t affect significantly. I think that it is not relevant.
    But perhaps you need rotate components to another angle, for example to obtain the radial and tangential components having into account the angle (azimuth) between and epicentre and station coordinates.

    3) Please, attach the response file(s) used to remove the instrument response and eventually the transfer command used, seems that a value is not correct (0.00000e+00).

    Saludos,

    Milton


    On 21 May 2019, at 22:00, Leticia Duca <leticiaduca<at>gmail.com> wrote:

    Dear,

    I have downloaded data from many events. I need to rotate and remove instrument response of all of them. I am using sac.

    1) Some of the events have the components called BH1 and BH2 (or BH2 and BH3) instead of BHE and BHN. To rotate, I need to know which one is BHE and which one BHN. For that, I watched the header information looking for CMPAZ=90 - CMPINC=90 for East component BHE, and CMPAZ=0 - CMPINC=90 for North component BHN.
    The problem was that in some cases the numbers of the CMPAZ were not the expected ones.
    Here I show you just two examples,
    Network Station Event BH1 (AZ—INC) BH2 (AZ—INC)
    2A 42 2002-11-15-mw66-south-georgia-island-region 0 – 90 0 – 90
    IU DWPF 2012-04-14-mw62-drake-passage 311 – 90 41 – 90

    2) Another problem appeared when the components BHE and BHN were not an orthogonal pair so I could not rotate. What shall I do in those cases? Can I just modify the CMPAZ value to make the pair orthogonal? Or I should look a solution in another way?
    For example:
    Network Station Event BHE (AZ) BHN (AZ)
    II ASCN 2004-12-22-mw60-southern-east-pacific-rise 93 2
    II SUR 2007-11-29-mw63-west-chile-rise 87,4 358,6

    3) I had a third problem when I tried to remove the instrument response on events occurred on 2012 and recorded by the TROLL station (NO network). The next error message appeared: "ERROR 2118: No transfer function applied. Unrecognized Constant: 0.000000 e+00". I did not know how to fix this.

    I have already written to Data Processing Help list, but they told me to write this list.
    I wish you could help me. Thank you in advance.
    Kind regards,


    Geof. Duca Freyre, Leticia
    Dpto. de Sismología e Inf. Meteorológica
    Facultad de Ciencias Astronómicas y Geofísicas
    Universidad Nacional de La Plata
    Tel: (+54) 221 4236593, int: 1155






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