Thread: Units for Wood-Anderson in transfer

Started: 2016-02-19 23:29:44
Last activity: 2017-09-28 01:20:26
Topics: SAC Help
Edgar Paz
2016-02-19 23:29:44
Hi, everyone! I'm working on a local magnitude scale and I need to convert data (which is in meters) to Wood-Anderson. I'm not sure if the parameters in transfer for Wood-Anderson (you know, when you write "transfer from none to wa") are set to nanometers, so when I read amplitudes I don't know if they're shown in meters or nanometers. Or maybe I should change my data in meters to nanometers just before using "transfer from none to wa"? Also, do you know how to find "src" to modify wa.c? I can't find it in the SAC directory... Any suggestions? Have a nice weekend!
  • Milton Plasencia
    2016-02-20 13:01:47
    Hi Edgar,

    It topics has been cover in the past, perhaps can you read an email of Chad Trabant
    of April 25, 2015 in https://ds.iris.edu/message-center/topic/sac-help/2015/4/

    The wa.c file in “source” sac distribution is in src/icm/wa.c
    here you can to change the values, i remember
    const_ = 2800 —> 2080
    h = 0.8 —> 0.7

    However, please first verify the bibliography values published in
    Uhrhammer, R. A., and Collins, E. R., 1990,
    Synthesis of Wood-Anderson seismograms from broadband digital records,
    Bulletin of the Seismological Society of America, v. 80, p. 702-716.
    are also the recommended values from the IASPEI recommendations in 2011.

    HTH,
    Milton



    On Feb 20, 2016, at 00:30, Edgar Paz <edgarpazmtz<at>gmail.com> wrote:

    Hi, everyone! I'm working on a local magnitude scale and I need to convert data (which is in meters) to Wood-Anderson. I'm not sure if the parameters in transfer for Wood-Anderson (you know, when you write "transfer from none to wa") are set to nanometers, so when I read amplitudes I don't know if they're shown in meters or nanometers. Or maybe I should change my data in meters to nanometers just before using "transfer from none to wa"? Also, do you know how to find "src" to modify wa.c? I can't find it in the SAC directory... Any suggestions? Have a nice weekend!

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    Attachments
    • Edgar Paz
      2016-02-26 19:02:32
      Helo, Mr. Plascencia,

      Thank you so much for you answer. I know it may be obvious, but I still can't find the source directory. I found a 'src' directory, but there's no 'icm' in it. Is it supposed to be in the SAC directory, I mean, the same where SAC is installed?
      • Milton Plasencia
        2016-02-27 04:14:32
        Hi Edgar,

        You must to download the source distribution of sac, not the binary one.
        you need the tar file sac-101.6a_source.tar.gz

        M.



        On Feb 26, 2016, at 20:02, Edgar Paz <edgarpazmtz<at>gmail.com> wrote:

        Helo, Mr. Plascencia,

        Thank you so much for you answer. I know it may be obvious, but I still can't find the source directory. I found a 'src' directory, but there's no 'icm' in it. Is it supposed to be in the SAC directory, I mean, the same where SAC is installed?

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        • Brian Savage
          2016-03-02 17:46:45
          Edgar,

          The equivalent pole-zero file for a Wood Anderson is (if I did the conversion properly)

          ZEROS 2
          POLES 2
          -6.283185307179586 4.712388980384689
          -6.283185307179586 -4.712388980384689
          CONSTANT 2800.0

          via src/icm/wa.c

          t0 = 0.8;
          h = 0.8;

          const_ = 2800.0;
          nzero = 2;
          npole = 2;

          om0 = M_PI * 2 / t0;
          rad = sqrt(1.0 - (h*h));

          Zero[1] = dbltocmplx(0.0, 0.0);
          Zero[2] = dbltocmplx(0.0, 0.0);

          Pole[1] = complex( -om0 * h, om0 * rad);
          Pole[2] = complex( -om0 * h, -om0 * rad);

          Cheers,
          Brian

          On Feb 26, 2016, at 8:15 PM, Milton Plasencia <mpplasencia<at>gmail.com> wrote:

          Hi Edgar,

          You must to download the source distribution of sac, not the binary one.
          you need the tar file sac-101.6a_source.tar.gz

          M.



          On Feb 26, 2016, at 20:02, Edgar Paz <edgarpazmtz<at>gmail.com> wrote:

          Helo, Mr. Plascencia,

          Thank you so much for you answer. I know it may be obvious, but I still can't find the source directory. I found a 'src' directory, but there's no 'icm' in it. Is it supposed to be in the SAC directory, I mean, the same where SAC is installed?

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          Sent via IRIS Message Center (http://ds.iris.edu/message-center/)
          Update subscription preferences at http://ds.iris.edu/account/profile/


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  • baigalaa@iag.ac.mn
    2017-09-27 06:00:26
    Hi, I need to convert data to Wood-Anderson seismograph. I removed instrument response using the RESP file and displacement unit was nanometre (I think). I'm not sure that what is should be unit just before using "transfer from none to WA? Is it millimetre, meter or nanometre?
    Also, i used WA pole-zero file in the SAC. (IASPEI recommendations in 2011; const=2080)
    • Milton Plasencia
      2017-09-28 01:20:26
      Hi,

      If you use RESP file you obtain meters.

      As said the transfer SAC manual, "For displacements, the SAC convention is
      nm."

      WA in sac have (at least as far as I know) const=2800 and h=0.8.

      HTH,

      M.




      ----------------------------
      Milton Plasencia
      mplasencia<at>inogs.it


      On Wed, Sep 27, 2017 at 5:17 PM, baigalaa<at>iag.ac.mn <baigalaa<at>iag.ac.mn>
      wrote:

      Hi, I need to convert data to Wood-Anderson seismograph. I removed
      instrument response using the RESP file and displacement unit was nanometre
      (I think). I'm not sure that what is should be unit just before using
      "transfer from none to WA? Is it millimetre, meter or nanometre?
      Also, i used WA pole-zero file in the SAC. (IASPEI recommendations in
      2011; const=2080)

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