Thread: Regarding "Scale" header in SAC (urgent)

Started: 2023-01-25 11:02:26
Last activity: 2023-01-27 07:13:32
Topics: SAC Help
Sushrat Mishra
2023-01-25 11:02:26
Respected Sir,
I have a query regarding the "Scale" header in SAC file.I have searched in
SAC manual but haven't got any clue. I am trying to convert the counts (raw
unit of seismogram) into some earth units(e.g. acceleration/velocity)
...For this exact factor is required.

I have gone through this link of IRIS
https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data/ &
found that its written, $SCALE=1m/s. I did the same thing with few
earthquake data recorded in "KATNP" station in Nepal & match the values
with the published paper
https://earth-planets-space.springeropen.com/articles/10.1186/s40623-016-0432-2
.

I observed that the value obtained after dividing $SCALE factor with the
data, matches well with the PGA (cm/s2) values mentioned in the paper than
PGV (cm/s).
Hence I doubt whether the conversion method mentioned here
https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data/
is right or wrong. Because according to this link, I should get value in
m/s or cm/s, but when I matched with already published paper result, the
value almost matches with the PGA values (in cm/s2).



Kindly help me in knowing, whether I will get the Velocity value (m/s) or
Acceleration (m/s2) after dividing with the $SCALE factor, at the earliest
of your convenience. I have attached a screen shot for your reference.

Thanking you!!


Yours Respectfully,
Sushrat Misha
Research scholar

Attachments
  • George Helffrich
    2023-01-26 17:45:09
    Dear Sushrat Misha -

    SAC does not use the SCALE value for any processing - it is essentially documentation. When reading GSE or CSS format data, a SCALE value in the input will, optionally, multiply the digital counts value. Otherwise SCALE will be filled in but not used.

    Except for reading GSE or CSS format data, SCALE is not used by SAC. GSE and CSS data use this value as a primitive form of instrument response. Nowadays, response information (EVALRESP or pole-zero responses) converts digital counts into a physical unit (velocity m/sec, nm/sec; displacement (m, nm) or acceleration (m/sec**2, nm/sec**2) and is the preferred way to describe data.

    On 26 Jan 2023, at 17:00, Sushrat Mishra (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:

    Respected Sir,
    I have a query regarding the "Scale" header in SAC file.I have searched in SAC manual but haven't got any clue. I am trying to convert the counts (raw unit of seismogram) into some earth units(e.g. acceleration/velocity) ...For this exact factor is required.

    I have gone through this link of IRIS https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data/ & found that its written, $SCALE=1m/s. I did the same thing with few earthquake data recorded in "KATNP" station in Nepal & match the values with the published paper https://earth-planets-space.springeropen.com/articles/10.1186/s40623-016-0432-2.

    I observed that the value obtained after dividing $SCALE factor with the data, matches well with the PGA (cm/s2) values mentioned in the paper than PGV (cm/s).
    Hence I doubt whether the conversion method mentioned here https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data/ is right or wrong. Because according to this link, I should get value in m/s or cm/s, but when I matched with already published paper result, the value almost matches with the PGA values (in cm/s2).



    Kindly help me in knowing, whether I will get the Velocity value (m/s) or Acceleration (m/s2) after dividing with the $SCALE factor, at the earliest of your convenience. I have attached a screen shot for your reference.

    Thanking you!!


    Yours Respectfully,
    Sushrat Misha
    Research scholar
    <20230119_205233.jpg>
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    George Helffrich
    george<at>elsi.jp


  • Hi Sushrat,
    KATNP appears to be a accelerometer used to record strong ground motion.
    Therefore, scale units are likely m/s^2. Please check and confirm what the
    scale units are.

    Januka

    Januka Attanayake
    Research Fellow/Lecturer | Earthquake Seismology Lead
    Homepage: *https://sites.google.com/site/janukaattanayake
    https://sites.google.com/site/janukaattanayake*

    School of Geography, Earth & Atmospheric Sciences
    University of Melbourne | Parkville 3010 VIC
    Australia




    On Fri, 27 Jan 2023 at 04:04, Sushrat Mishra (via IRIS) <
    sac-help-bounce<at>lists.ds.iris.edu> wrote:

    Respected Sir,
    I have a query regarding the "Scale" header in SAC file.I have searched in
    SAC manual but haven't got any clue. I am trying to convert the counts
    (raw unit of seismogram) into some earth units(e.g. acceleration/velocity)
    ...For this exact factor is required.

    I have gone through this link of IRIS
    https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data/
    & found that its written, $SCALE=1m/s. I did the same thing with few
    earthquake data recorded in "KATNP" station in Nepal & match the values
    with the published paper
    https://earth-planets-space.springeropen.com/articles/10.1186/s40623-016-0432-2
    .

    I observed that the value obtained after dividing $SCALE factor with the
    data, matches well with the PGA (cm/s2) values mentioned in the paper than
    PGV (cm/s).
    Hence I doubt whether the conversion method mentioned here
    https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data/
    is right or wrong. Because according to this link, I should get value in
    m/s or cm/s, but when I matched with already published paper result, the
    value almost matches with the PGA values (in cm/s2).



    Kindly help me in knowing, whether I will get the Velocity value (m/s) or
    Acceleration (m/s2) after dividing with the $SCALE factor, at the earliest
    of your convenience. I have attached a screen shot for your reference.

    Thanking you!!


    Yours Respectfully,
    Sushrat Misha
    Research scholar

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10:35:07 v.22510d55