Thread: Re: PGA

Started: 2022-03-01 09:32:36
Last activity: 2022-03-01 23:01:42
Topics: SAC Help
Sheila Peacock
2022-03-01 09:32:36
Dear Nima,

if your seismic traces have already been multiplied by the calibration factor in m/s^2/count (some programs for converting data to SAC format do this and some don't) then you need to run the SAC "transfer" command "transfer from polezero subtype filename to none freqlimits f1 f2 f3 f4: (type "help transfer" at the SAC prompt to get help). "filename" should be the filename of a file containing the poles and zeros like this:

POLES n
re im
re im
re im
...
ZEROS m
re im
re im
re im
...
CONSTANT pole-zero constant (also called "A0 normalization factor")

The constant (A0 normalization factor) should be in the SEED header if your data are SEED (use rdseed -s to view it) or in the Guralp calibration sheet. Don't forget to multiply the poles and zeros by 2pi if they're from the Guralp sheet because they need to be in radians for SAC, and if you get the pole-zero constant (A0 normalization factor) from the Guralp sheet you need to multiply it by 2pi^(n-m) where n is the number of poles and m is the number of zeros.

(Can other readers please check that I have got this formula right? Thanks!)

The digital samples will then be in units of acceleration. I do not know what further processing is needed to get PEAK ground acceleration. Perhaps consult the SAC manual online at IRIS for inspiration - ? http://ds.iris.edu/files/sac-manual/

Regards,
Sheila Peacock.


On 1 Mar 2022, at 05:52, Nima Dolatabadi <syn_org939<at>rocketmail.com> wrote:

Dear Sheila,
I just got interested in this issue, if we consider that the calibration is done; I wonder how is it possible to calculate PGA using SAC? (The first time I'm hearing that).
Is there any manual to do so? I've read the SAC manual and got no idea about it.
Regards.


________________________

Nima Dolatabadi

M.Sc., Geophysics

Institute of Geophysics

University of Tehran

Tehran, Iran




On Mon, Feb 28, 2022 at 12:22, Sheila Peacock (via IRIS)
<sac-help-bounce<at>lists.ds.iris.edu> wrote:

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  • Ali Solihat
    2022-03-01 23:01:42
    Many thanks.

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    ________________________________
    From: sac-help-bounce<at>lists.ds.iris.edu <sac-help-bounce<at>lists.ds.iris.edu> on behalf of Sheila Peacock (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu>
    Sent: Tuesday, March 1, 2022 12:34:02 PM
    To: SAC Help <sac-help<at>lists.ds.iris.edu>
    Subject: Re: [IRIS][sac-help] PGA

    Dear Nima,

    if your seismic traces have already been multiplied by the calibration factor in m/s^2/count (some programs for converting data to SAC format do this and some don't) then you need to run the SAC "transfer" command "transfer from polezero subtype filename to none freqlimits f1 f2 f3 f4: (type "help transfer" at the SAC prompt to get help). "filename" should be the filename of a file containing the poles and zeros like this:

    POLES n
    re im
    re im
    re im
    ...
    ZEROS m
    re im
    re im
    re im
    ...
    CONSTANT pole-zero constant (also called "A0 normalization factor")

    The constant (A0 normalization factor) should be in the SEED header if your data are SEED (use rdseed -s to view it) or in the Guralp calibration sheet. Don't forget to multiply the poles and zeros by 2pi if they're from the Guralp sheet because they need to be in radians for SAC, and if you get the pole-zero constant (A0 normalization factor) from the Guralp sheet you need to multiply it by 2pi^(n-m) where n is the number of poles and m is the number of zeros.

    (Can other readers please check that I have got this formula right? Thanks!)

    The digital samples will then be in units of acceleration. I do not know what further processing is needed to get PEAK ground acceleration. Perhaps consult the SAC manual online at IRIS for inspiration - ? http://ds.iris.edu/files/sac-manual/

    Regards,
    Sheila Peacock.


    On 1 Mar 2022, at 05:52, Nima Dolatabadi <syn_org939<at>rocketmail.com<syn_org939<at>rocketmail.com>> wrote:

    Dear Sheila,
    I just got interested in this issue, if we consider that the calibration is done; I wonder how is it possible to calculate PGA using SAC? (The first time I'm hearing that).
    Is there any manual to do so? I've read the SAC manual and got no idea about it.
    Regards.


    ________________________

    Nima Dolatabadi

    M.Sc., Geophysics

    Institute of Geophysics

    University of Tehran

    Tehran, Iran




    On Mon, Feb 28, 2022 at 12:22, Sheila Peacock (via IRIS)
    <sac-help-bounce<at>lists.ds.iris.edu<sac-help-bounce<at>lists.ds.iris.edu>> wrote:

    ----------------------
    SAC Help
    Topic home: http://ds.iris.edu/message-center/topic/sac-help/ | Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu<sac-help-unsubscribe<at>lists.ds.iris.edu>

    Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
    Update subscription preferences at http://ds.iris.edu/account/profile/


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