[SAC-HELP] finding difficulty in rotation

[Fiona Darbyshire]

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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