Thread: Rotating BH1 BH2

Started: 2020-06-05 10:39:54
Last activity: 2020-06-07 10:31:37
Topics: SAC Help
ANURIMA MISHRA
2020-06-05 10:39:54
Hello,
I have downloaded several sac files for an event. The sac files contain
BHE, BHN for some stations and BH1, BH2 for others. When I am rotating the
BHE,BHN components, they are rotating fine, but the BH1 BH2 are not. After
rotation, I could see that both the components are looking similar, which
should not be the case if rotated fine. I have checked the header. I could
not find any unusual parameter. I am attaching the pdf files for BH1, BH2
components for a station TIXI (network IU) and BHE, BHN components for a
station GTA (network CB). I am also attaching the raw sac files for both of
these stations.
Waiting for your reply.

Cheers
Anurima Mishra
Senior Research Fellow
Department of Earth Sciences
Indian Institute of Technology, Bombay
400076
Maharastra, India

  • Milton Plasencia
    2020-06-05 23:38:47
    Hi Anurima,
    BHN and BHE are oriented in the North and East direction respectively.

    But BH1 and BH2 must be oriented with angles greater than 5 degrees from
    North and East respectively.
    I invite you to read the page 134 of SEED Manual (
    http://www.fdsn.org/pdf/SEEDManual_V2.4.pdf)

    In your particular case for TIXI station the azimuth is 0 for channel BH1,
    (so coincides with BHN and so on).

    HTH,

    Milton


    ************************************
    Milton P. PLASENCIA LINARES
    Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS
    Borgo Grotta Gigante 42/C
    (34010) Sgonico - Trieste - Italia
    Tel: +39 040 2140 156 (Udine)
    Tel: +39 040 2140 256 (Trieste)
    Cell.: +39 331 6481 935

    E-mail: mplasencia<at>inogs.it

    Antarctic Seismographic Argentinean Italian Network (ASAIN)
    **************************************


    On Fri, 5 Jun 2020 at 22:03, ANURIMA MISHRA (via IRIS) <
    sac-help<at>lists.ds.iris.edu> wrote:

    Hello,
    I have downloaded several sac files for an event. The sac files contain
    BHE, BHN for some stations and BH1, BH2 for others. When I am rotating the
    BHE,BHN components, they are rotating fine, but the BH1 BH2 are not. After
    rotation, I could see that both the components are looking similar, which
    should not be the case if rotated fine. I have checked the header. I could
    not find any unusual parameter. I am attaching the pdf files for BH1, BH2
    components for a station TIXI (network IU) and BHE, BHN components for a
    station GTA (network CB). I am also attaching the raw sac files for both of
    these stations.
    Waiting for your reply.

    Cheers
    Anurima Mishra
    Senior Research Fellow
    Department of Earth Sciences
    Indian Institute of Technology, Bombay
    400076
    Maharastra, India

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    • ANURIMA MISHRA
      2020-06-07 10:31:37
      Thank you very much fro your reply Milton. My confusion was, similar
      looking BH1 and BH2 after rotation, when they should look more like a
      mirror image of each other. Which is not the case for TIXI as we can see.
      But for GTA, the SH and SV are deflecting in opposite direction after
      rotation, as the components for GTA were BHE and BHN. The manual you sent
      was really helpful, as it showed that there could be a polarity reversal in
      the signals while recording. I believe, I need to revert the polarity of
      one component to get the useful signal after rotation.

      Cheers

      Anurima

      On Sat, Jun 6, 2020 at 3:14 AM Milton Plasencia (via IRIS) <
      sac-help<at>lists.ds.iris.edu> wrote:

      Hi Anurima,
      BHN and BHE are oriented in the North and East direction respectively.

      But BH1 and BH2 must be oriented with angles greater than 5 degrees from
      North and East respectively.
      I invite you to read the page 134 of SEED Manual (
      http://www.fdsn.org/pdf/SEEDManual_V2.4.pdf)

      In your particular case for TIXI station the azimuth is 0 for channel BH1,
      (so coincides with BHN and so on).

      HTH,

      Milton


      ************************************
      Milton P. PLASENCIA LINARES
      Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS
      Borgo Grotta Gigante 42/C
      (34010) Sgonico - Trieste - Italia
      Tel: +39 040 2140 156 (Udine)
      Tel: +39 040 2140 256 (Trieste)
      Cell.: +39 331 6481 935

      E-mail: mplasencia<at>inogs.it

      Antarctic Seismographic Argentinean Italian Network (ASAIN)
      **************************************


      On Fri, 5 Jun 2020 at 22:03, ANURIMA MISHRA (via IRIS) <
      sac-help<at>lists.ds.iris.edu> wrote:

      Hello,
      I have downloaded several sac files for an event. The sac files contain
      BHE, BHN for some stations and BH1, BH2 for others. When I am rotating the
      BHE,BHN components, they are rotating fine, but the BH1 BH2 are not. After
      rotation, I could see that both the components are looking similar, which
      should not be the case if rotated fine. I have checked the header. I could
      not find any unusual parameter. I am attaching the pdf files for BH1, BH2
      components for a station TIXI (network IU) and BHE, BHN components for a
      station GTA (network CB). I am also attaching the raw sac files for both of
      these stations.
      Waiting for your reply.

      Cheers
      Anurima Mishra
      Senior Research Fellow
      Department of Earth Sciences
      Indian Institute of Technology, Bombay
      400076
      Maharastra, India

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