Thread: Need Help.

Started: 2017-10-28 16:38:18
Last activity: 2017-10-31 18:16:06
Topics: SAC Help
Mukesh Das
2017-10-28 16:38:18
Hi sac users,

I have computed Ps receiver function in which maximum amplitude (direct
P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum
amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude
at 0 sec. Here below i have attached some screen shot of receiver function
in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

Thanks

--
Mukesh Kumar Das
JRF (Research Scholar)
Department of Applied Geophysics
Indian lnstitute of Technology (Indian School of Mines)
Dhanbad, Jharkhand-826004, India
Mob +918873563108
+918340601230

  • Craig Jones
    2017-10-28 06:37:06
    You don't say how this receiver function was made, but if a
    single station receiver function, your logic is flawed, I think.
    The maximum amplitude on a Ps RF need not be the direct
    arrival. In fact, if you are rotating into coordinates parallel
    and normal to the P arrival, it will certainly not be the direct
    arrival. If the station has a low velocity underneath it, the
    arrival will come in nearly vertically and, once again, the peak
    arrival will not be the direct P.

    The only time you will not have the direct arrival at 0 seconds
    on a single station RF is when you have a timing error on one
    component or another, which is a profoundly unlikely occurence.
    You can end up with an offset if you are deconvolving a
    different P wave (e.g., one made by beamforming over a
    collection of stations) from a single station radial component.

    If you still want to shift things, all that is involved is
    playing with the relevant header variables for a SAC file (it
    depends a bit on what you are planning on doing afterwards as to
    the best combination of changes to make).

    On 10/28/17 at 10:09 PM, kumarmukesh2411<at>gmail.com (mukesh
    kumar) wrote:

    Hi sac users,

    I have computed Ps receiver function in which maximum amplitude (direct
    P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum
    amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude
    at 0 sec. Here below i have attached some screen shot of receiver function
    in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

    Thanks

    --
    Craig H. Jones
    Professor, Dept. Geological Sciences, CB 399
    and Fellow, CIRES, CB 216
    University of Colorado, Boulder, CO 80309-0399
    http://cires1.colorado.edu/people/jones.craig/


    • Steve Gao
      2017-10-30 23:29:47
      I agree. The shift is most likely an indication of the existence of a loose sedimentary layer. This is especially true if the receiver function is dominated by reverberations. This has been discussed in Yeck et al. (2013) and Yu et al. (2015). The latter is attached for your convenience -- see Figure 2a for a synthetic example.

      Steve Gao


      Stephen S. Gao, Professor, 
      Geology & Geophysics Program,
      Missouri University of Science & Technology,
      129 McNutt Hall, Rolla, Missouri 65409, USA
      E-mail: sgao<at>mst.edu 
      Office Phone: (573)-341-6676  
      http://web.mst.edu/~sgao     

       
      -----Original Message-----
      From: sac-help-bounce<at>iris.washington.edu [sac-help-bounce<at>iris.washington.edu] On Behalf Of Craig Jones
      Sent: Monday, October 30, 2017 11:04 AM
      To: SAC Help <sac-help<at>lists.ds.iris.edu>
      Subject: Re: [IRIS][sac-help] Need Help.

      You don't say how this receiver function was made, but if a single station receiver function, your logic is flawed, I think.
      The maximum amplitude on a Ps RF need not be the direct arrival. In fact, if you are rotating into coordinates parallel and normal to the P arrival, it will certainly not be the direct arrival. If the station has a low velocity underneath it, the arrival will come in nearly vertically and, once again, the peak arrival will not be the direct P.

      The only time you will not have the direct arrival at 0 seconds on a single station RF is when you have a timing error on one component or another, which is a profoundly unlikely occurence.
      You can end up with an offset if you are deconvolving a different P wave (e.g., one made by beamforming over a collection of stations) from a single station radial component.

      If you still want to shift things, all that is involved is playing with the relevant header variables for a SAC file (it depends a bit on what you are planning on doing afterwards as to the best combination of changes to make).

      On 10/28/17 at 10:09 PM, kumarmukesh2411<at>gmail.com (mukesh
      kumar) wrote:

      Hi sac users,

      I have computed Ps receiver function in which maximum amplitude (direct
      P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift
      maximum amplitude at 0 sec. Can anyone suggest how to shift this
      maximum amplitude at 0 sec. Here below i have attached some screen shot
      of receiver function in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

      Thanks

      --
      Craig H. Jones
      Professor, Dept. Geological Sciences, CB 399 and Fellow, CIRES, CB 216 University of Colorado, Boulder, CO 80309-0399 http://cires1.colorado.edu/people/jones.craig/


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      • Mukesh Das
        2017-10-31 18:16:06
        Hi Craig,

        We computed these receiver functions using iterative time domain
        deconvolution with Gaussian width 1.5. We also rotated our seismograms from
        ZNE to ZRT components. Do you think if we will use Gaussian width of 2.0 or
        above then we can probably see clear arrival of direct P-wave exactly at
        zero then Ps phase due to sediment basement after 1-2 seconds (if basement
        depth is more than 1km).


        Regards,

        On Mon, Oct 30, 2017 at 10:01 PM, Steve Gao <sgao<at>mst.edu> wrote:

        I agree. The shift is most likely an indication of the existence of a
        loose sedimentary layer. This is especially true if the receiver function
        is dominated by reverberations. This has been discussed in Yeck et al.
        (2013) and Yu et al. (2015). The latter is attached for your convenience --
        see Figure 2a for a synthetic example.

        Steve Gao


        Stephen S. Gao, Professor,
        Geology & Geophysics Program,
        Missouri University of Science & Technology,
        129 McNutt Hall, Rolla, Missouri 65409, USA
        E-mail: sgao<at>mst.edu
        Office Phone: (573)-341-6676
        http://web.mst.edu/~sgao


        -----Original Message-----
        From: sac-help-bounce<at>iris.washington.edu [mailto:sac-help-bounce@iris.
        washington.edu] On Behalf Of Craig Jones
        Sent: Monday, October 30, 2017 11:04 AM
        To: SAC Help <sac-help<at>lists.ds.iris.edu>
        Subject: Re: [IRIS][sac-help] Need Help.

        You don't say how this receiver function was made, but if a single station
        receiver function, your logic is flawed, I think.
        The maximum amplitude on a Ps RF need not be the direct arrival. In fact,
        if you are rotating into coordinates parallel and normal to the P arrival,
        it will certainly not be the direct arrival. If the station has a low
        velocity underneath it, the arrival will come in nearly vertically and,
        once again, the peak arrival will not be the direct P.

        The only time you will not have the direct arrival at 0 seconds on a
        single station RF is when you have a timing error on one component or
        another, which is a profoundly unlikely occurence.
        You can end up with an offset if you are deconvolving a different P wave
        (e.g., one made by beamforming over a collection of stations) from a single
        station radial component.

        If you still want to shift things, all that is involved is playing with
        the relevant header variables for a SAC file (it depends a bit on what you
        are planning on doing afterwards as to the best combination of changes to
        make).

        On 10/28/17 at 10:09 PM, kumarmukesh2411<at>gmail.com (mukesh
        kumar) wrote:

        Hi sac users,

        I have computed Ps receiver function in which maximum amplitude (direct
        P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift
        maximum amplitude at 0 sec. Can anyone suggest how to shift this
        maximum amplitude at 0 sec. Here below i have attached some screen shot
        of receiver function in which maximum amplitude (direct P- wave arrival)
        come at after 2-3 sec.

        Thanks

        --
        Craig H. Jones
        Professor, Dept. Geological Sciences, CB 399 and Fellow, CIRES, CB 216
        University of Colorado, Boulder, CO 80309-0399 http://cires1.colorado.edu/
        people/jones.craig/


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        --
        Mukesh Kumar Das
        JRF (Research Scholar)
        Department of Applied Geophysics
        Indian lnstitute of Technology (Indian School of Mines)
        Dhanbad, Jharkhand-826004, India
        Mob +918873563108
        +918340601230

  • Geo .
    2017-10-28 16:05:47
    Hi Mukesh,
    You can use the inline function GETTIME to obtain the xx value George
    mentioned. You may refer the SAC manual for usage. Note that your P wave
    peak is recorded in the header DEPMAX if it is the largest amplitude in
    your RFs, which usually is true unless you have very noisy RFs. You can
    easily automate this process with a macro.

    https://ds.iris.edu/files/sac-manual/manual/inline.html

    Januka

    On Saturday, 28 October 2017, mukesh kumar <kumarmukesh2411<at>gmail.com>
    wrote:

    Hi sac users,

    I have computed Ps receiver function in which maximum amplitude (direct
    P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum
    amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude
    at 0 sec. Here below i have attached some screen shot of receiver function
    in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

    Thanks

    --
    Mukesh Kumar Das
    JRF (Research Scholar)
    Department of Applied Geophysics
    Indian lnstitute of Technology (Indian School of Mines)
    Dhanbad, Jharkhand-826004, India
    Mob +918873563108
    +918340601230



    --
    Januka Attanayake
    Postdoctoral Research Associate

    Institute for Geophysics
    WWU Münster | CorrensstraBe 24 | 48149 Münster | Germany
    Tel +49 251 833 4727

    University email: jattanayake<at>uni-muenster.de
    Homepage: http://sites.google.com/site/janukaattanayake/

    • Mukesh Das
      2017-10-29 18:05:06
      Thank you everyone for your valuable suggestion.

      On Sat, Oct 28, 2017 at 12:36 PM, Geo . <jattanayake<at>gmail.com> wrote:

      Hi Mukesh,
      You can use the inline function GETTIME to obtain the xx value George
      mentioned. You may refer the SAC manual for usage. Note that your P wave
      peak is recorded in the header DEPMAX if it is the largest amplitude in
      your RFs, which usually is true unless you have very noisy RFs. You can
      easily automate this process with a macro.

      https://ds.iris.edu/files/sac-manual/manual/inline.html

      Januka

      On Saturday, 28 October 2017, mukesh kumar <kumarmukesh2411<at>gmail.com>
      wrote:

      Hi sac users,

      I have computed Ps receiver function in which maximum amplitude (direct
      P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum
      amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude
      at 0 sec. Here below i have attached some screen shot of receiver function
      in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

      Thanks

      --
      Mukesh Kumar Das
      JRF (Research Scholar)
      Department of Applied Geophysics
      Indian lnstitute of Technology (Indian School of Mines)
      Dhanbad, Jharkhand-826004, India
      Mob +918873563108
      +918340601230



      --
      Januka Attanayake
      Postdoctoral Research Associate

      Institute for Geophysics
      WWU Münster | CorrensstraBe 24 | 48149 Münster | Germany
      Tel +49 251 833 4727

      University email: jattanayake<at>uni-muenster.de
      Homepage: http://sites.google.com/site/janukaattanayake/



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      Topic home: http://ds.iris.edu/message-center/topic/sac-help/ |
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      --
      Mukesh Kumar Das
      JRF (Research Scholar)
      Department of Applied Geophysics
      Indian lnstitute of Technology (Indian School of Mines)
      Dhanbad, Jharkhand-826004, India
      Mob +918873563108
      +918340601230

  • George Helffrich
    2017-10-28 22:51:16
    Dear Mukesh Das -

    Use CH B xx where xx is the time difference between zero and your peak. That shifts the data start time to a new value relative to the file's zero time.

    On 28 Oct 2017, at 13:09, mukesh kumar <kumarmukesh2411<at>gmail.com> wrote:

    Hi sac users,

    I have computed Ps receiver function in which maximum amplitude (direct P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude at 0 sec. Here below i have attached some screen shot of receiver function in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

    Thanks

    --
    Mukesh Kumar Das
    JRF (Research Scholar)
    Department of Applied Geophysics
    Indian lnstitute of Technology (Indian School of Mines)
    Dhanbad, Jharkhand-826004, India
    Mob +918873563108
    +918340601230
    <Screenshot from 2017-10-27 22-34-30.png><Screenshot from 2017-10-27 22-35-18.png><Screenshot from 2017-10-27 22-37-06.png><Screenshot from 2017-10-27 22-38-19.png>
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    George Helffrich
    george<at>elsi.jp


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