Thread: Transfer-freq limits

Started: 2016-02-16 01:05:07
Last activity: 2016-02-16 01:05:07
Topics: SAC Help
Hamdi ALKAN
2016-02-16 01:05:07
Dear all,
I try to remove the instrument response for seismograms obtained from IRIS,
ORFEUS.
These seismograms (Full Seed waveform) recorded KOERI broadband stations.
The stations have CMG-3T sensors (120 sec).
For this purpose, I have utilised rdseed, evalresp and SAC programs.
So, I have used following SAC command to remove instrument response;

*rtr*

*taper*

*transfer from evalresp (resp file) to none freqlim 0.01 0.02 0.2 0.4. *


I am not sure this process because of the frequency limits.
I searched Guralp web page for frequency response curves. But, have not
find the curves.

My question is What or How do I choose the F1, F2, F3 and F4 values?

Please help me to select freq limits.

Thank you for everyone.


--
Res. Asst. Hamdi ALKAN
Yüzüncü Yıl University
Faculty of Engineering and Architecture
Department of Geophysical Engineering
65080 Van/TURKEY
Tel num: 0 (432) 225 17 26
e-mail: hamdialkan<at>yyu.edu.tr
halkan65<at>gmail.com

  • Philip Crotwell
    2016-02-15 19:41:40
    Hi

    120 sec = 0.0083Hz so for F1, F2 you might choose something like 0.004
    and 0.008 to catch all of the "flat" part of the sensor. Usually
    people don't care so much about the high end, so choose F3 large, ie >
    nyquist and F4 = 2*F3.

    But, frequency limits for transfer are a bit of a black art, and
    depending on noise levels and such you may need to bring the low end
    up to avoid long period numerical ringing, maybe try 0.005 and 0.010
    or even larger if needed.

    Good rule of thumb is F2 = 2* F1 and F4 = 2* F3, so really just pick
    F2, F3 to be your frequency window of interest and then get F1 and F4
    from them.

    Also, manual is here:
    http://ds.iris.edu/files/sac-manual/commands/transfer.html

    Philip

    On Mon, Feb 15, 2016 at 10:06 AM, Hamdi ALKAN <halkan65<at>gmail.com> wrote:
    Dear all,

    I try to remove the instrument response for seismograms obtained from IRIS,
    ORFEUS.
    These seismograms (Full Seed waveform) recorded KOERI broadband stations.
    The stations have CMG-3T sensors (120 sec).
    For this purpose, I have utilised rdseed, evalresp and SAC programs.
    So, I have used following SAC command to remove instrument response;

    rtr

    taper

    transfer from evalresp (resp file) to none freqlim 0.01 0.02 0.2 0.4.



    I am not sure this process because of the frequency limits.
    I searched Guralp web page for frequency response curves. But, have not find
    the curves.

    My question is What or How do I choose the F1, F2, F3 and F4 values?

    Please help me to select freq limits.

    Thank you for everyone.



    --
    Res. Asst. Hamdi ALKAN
    Yüzüncü Yıl University
    Faculty of Engineering and Architecture
    Department of Geophysical Engineering
    65080 Van/TURKEY
    Tel num: 0 (432) 225 17 26
    e-mail: hamdialkan<at>yyu.edu.tr
    halkan65<at>gmail.com


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04:42:23 v.f0c1234e