Thread: finding difficulty in rotation

Started: 2007-03-26 15:47:43
Last activity: 2007-03-26 15:47:43
Topics: SAC Help
kawsar laskar
2007-03-26 15:47:43
hello Sir,
I m an M.Tech student of computational seismology. I
am using SAC for receiver function analysis .I am
finding difficulty in performing rotation of NS and EW
component to radial and tangential components.
whenever I try the command "rot to gcp"an error
message telling both the components are not horizontal
comes.

what is the wrong with that.Is there anything wrong
with the command or data .what should I do now please advise.



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  • Fiona Darbyshire
    2007-03-26 11:38:39
    Hi,

    Check the SAC headers (type "lh") - if the information about the components
    is incorrect, then SAC won't recognise the north and east components as
    horizontals. For the NS component you should see CMPAZ 0.0 CMPINC 90.0 and
    for the EW component CMPAZ 90.0 CMPINC 90.0 if I remember rightly (I'm
    temporarily without access to SAC at the moment, so any other users please
    correct me if I've got this the wrong way around!).

    If the values are incorrect, use the "ch" command to change them, then "wh"
    to save the new header information. e.g. if you have multiple seismograms:

    SAC> r *HN
    SAC> ch cmpaz 0.0 cmpinc 90.0
    SAC> wh
    SAC> r *HE
    SAC> ch cmpaz 90.0 cmpinc 90.0
    SAC> wh

    Hope this helps. If those header fields are correct, perhaps you could send
    a transcript of the header to the sac-help list; that would help with
    diagnosis.

    Fiona.

    On 3/26/07, kawsar laskar <kawsarl<at>yahoo.co.in> wrote:

    hello Sir,
    I m an M.Tech student of computational seismology. I
    am using SAC for receiver function analysis .I am
    finding difficulty in performing rotation of NS and EW
    component to radial and tangential components.
    whenever I try the command "rot to gcp"an error
    message telling both the components are not horizontal
    comes.

    what is the wrong with that.Is there anything wrong
    with the command or data .what should I do now please advise.



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    http://in.answers.yahoo.com/
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