Thread: remove instrument response

Started: 2016-09-13 23:07:44
Last activity: 2016-09-14 15:34:12
Topics: SAC Help
kejie
2016-09-13 23:07:44
To whom it may concern:

I just downloaded SAC and SACPZ file from IRIS Wilber. What I want is ground motion velocity during earthquake times, So I run the following:

r sacfilename
rmean
taper
transfer from polezero subtype PZfile to vel freqlimits 0.001 0.002 40 50

My question is:

Is the result unit m/s?
How should I determine the freqlimits? In the further step, I am also going to do a band passing for the velocity time series.

All the best!

Kejie
  • Milton Plasencia
    2016-09-14 13:35:15
    Hi

    see below,

    M.

    * * * * * * * * * * * * * * * * * * * * * * *
    Milton P. PLASENCIA LINARES

    Centro di Ricerche Sismologiche (CRS)
    OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale

    Borgo Grotta Gigante 42/C
    (34010) Sgonico - Trieste - Italia
    Tel: +39 040 2140 156 (Udine)
    Tel: +39 040 2140 256 (Trieste)
    Cel.: +39 331 6481 935

    E-mail: mplasencia<at>inogs.it
    GPG key: 22FCFFA8

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

    On Sep 14, 2016, at 01:45, kejie <whuckj<at>gmail.com> wrote:

    To whom it may concern:

    I just downloaded SAC and SACPZ file from IRIS Wilber. What I want is ground motion velocity during earthquake times, So I run the following:

    r sacfilename
    rmean
    taper
    transfer from polezero subtype PZfile to vel freqlimits 0.001 0.002 40 50

    My question is:

    Is the result unit m/s?
    YES

    How should I determine the freqlimits? In the further step, I am also going to do a band passing for the velocity time series.
    Freqlimits must be choice depending the frequency band of your instrument.
    In your case you assume a band of 1000 to 0.02 seconds, it seems not realistic, but i do not know instrument with 1000 sec of period.
    so, assuming you have an instrument from 100 s to 50 Hz , the freqlimits should be 0.01 0.02 40 45 for example.

    HTH,

    Milton


    All the best!

    Kejie

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    • Arthur Snoke
      2016-09-14 15:34:12
      SAC treats any polezero file as though it were a transfer function between counts and displacement, so using one prepared for use in SAC by an external source will not be changed by putting “to gel” in the transfer line. In order to get el or acc from transfer with a from polezero option one must alter the number of zeros in the numerator of the poolezero file.

      The from evalresp call in transfer, which uses a RESP file produced by RDSEED, will change response depending on to gel or to acc etc. SAC’s implementation of EVALRESP also corrects the units from the rest of the world’s m or m/s to nm or nm/s. The polezero option does not.

      Milton gives good advice on choosing FREQLIMITS. For fine-tuning, I compare spectra for a desired waveform with the noise window before it with the same length and filtering.

      These questions come up a lot on sac-help, and we have revised the TRANSFER help file to try to clarify these issues. It will come out in the revised manual with the next SAC update, but attached is a copy.

      On Sep 14, 2016, at 12:36 AM, Milton Plasencia <mplasencia<at>inogs.it> wrote:

      Hi

      see below,

      M.
      * * * * * * * * * * * * * * * * * * * * * * *
      Milton P. PLASENCIA LINARES

      Centro di Ricerche Sismologiche (CRS)
      OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale

      Borgo Grotta Gigante 42/C
      (34010) Sgonico - Trieste - Italia
      Tel: +39 040 2140 156 (Udine)
      Tel: +39 040 2140 256 (Trieste)
      Cel.: +39 331 6481 935

      E-mail: mplasencia<at>inogs.it <mplasencia<at>inogs.it>
      GPG key: 22FCFFA8

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

      On Sep 14, 2016, at 01:45, kejie <whuckj<at>gmail.com <whuckj<at>gmail.com>> wrote:

      To whom it may concern:

      I just downloaded SAC and SACPZ file from IRIS Wilber. What I want is ground motion velocity during earthquake times, So I run the following:

      r sacfilename
      rmean
      taper
      transfer from polezero subtype PZfile to vel freqlimits 0.001 0.002 40 50

      My question is:

      Is the result unit m/s?
      YES

      How should I determine the freqlimits? In the further step, I am also going to do a band passing for the velocity time series.
      Freqlimits must be choice depending the frequency band of your instrument.
      In your case you assume a band of 1000 to 0.02 seconds, it seems not realistic, but i do not know instrument with 1000 sec of period.
      so, assuming you have an instrument from 100 s to 50 Hz , the freqlimits should be 0.01 0.02 40 45 for example.

      HTH,

      Milton


      All the best!

      Kejie


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