Thread: SAC macro for power-spectral-density (noise) plots for seismograph stations

Started: 2011-02-17 18:50:48
Last activity: 2011-03-22 00:04:51
Topics: SAC Help
Hello,

Several years ago, I tried making power-spectral-density plots for
noise characteristics of temporary seismograph stations, but it's been
many years since I did this, and I have forgotten the details. One of
my colleagues just sent me a copy of my original macro to ask me about
it, and I find myself second-guessing myself as to whether I did it
right originally. Here's the relevant section of the macro and my
query:

cut 0 1000
r 2011.038.17.00.00.0000.CN.YUK1..HHZ.D.SAC
cut off
transfer from polezero subtype yuk1.pz to none freqlim 0.005 0.006 40 45
dft
divomega
keepam
xlim 0.01 50
div 27.38613
sqr
add 1e-12
log10
mul 10
loglin
p2

When I look more closely at the TRANSFER documentation, I see that if
I transfer to NONE, the result should be a displacement seismogram.
But the divomega in the frequency domain is an integration, so
presumably I was thinking of converting from velocity to displacement
there... does that mean I've effectively integrated twice?
(I also can't remember what the division by 27.3 was for, though my
suspicion is that it was some kind of normalisation...)

If anyone can advise me on this, or anyone has a better SAC macro for
PSD that they're willing to share, please let me know!

Thanks very much,

Fiona Darbyshire
Université du Québec à Montréal



  • Dear colleagues,

    Recently we transferred some waveform records from IRIS. These records generated by the same earthquake do not have the same start time. As we need all the records generated by the same earthquake have the same start time to make measurement we tried to use sac2000 function synchronize. After we used the function and used lh we found all the ktime? are same. When we display those waveform records processed by the function synchronize, we found the original start times are still kept.
    Could you tell me how to use the synchronize function effectively?
    Do you have another way to make all the records generated by the same earthquake have the same start time?
    Thanks in advance,
    Shutian


    • Januka Attanayake
      2011-03-21 20:46:16
      If you want to recover the  zero padded "whole" trace you could use the OMARKER header. It's the length of time missing from the sac trace that you download from IRIS. For example, you might be able to use something like the following macro -- adds zeros from the origin time to the starting point of your trace using cuterr fillz. I am guessing this will automatically adjust your start time but please double check and modify as needed.

      DO FILE WILD *.BHZ.R.SAC*
        READ $FILE
        SETBB OMKR &1,OMARKER
        GETBB OMKR

        xlim T0 -10 10
        p
        CUT ON
        CUTERR FILLZ
        CUT b %OMKR e
        READ $FILE
        WRITE OVER
      ENDDO
      CUT OFF

      _______________Serenity isn't freedom from the storm, but peace within the storm
      Januka Attanayake  Global Seismology & Economics
      The University of Connecticut
      Beach Hall - U2045
      354, Mansfield Rd;
      Storrs, CT 06269
      Tel :  860 486 0475 (Office)
                860 486 3914 (Lab - P405)
      URL: http://sites.google.com/site/janukaattanayake/






      --- On Mon, 3/21/11, Shutian Ma <shutian33<at>yahoo.ca> wrote:

      From: Shutian Ma <shutian33<at>yahoo.ca>
      Subject: [SAC-HELP] how to use sac function synchronize effectively
      To: sac-help<at>iris.washington.edu
      Date: Monday, March 21, 2011, 9:47 AM


      Dear colleagues,

      Recently we transferred some waveform records from IRIS. These records generated by the same earthquake do not have the same start time. As we need all the records generated by the same earthquake have the same start time to make measurement we tried to use sac2000 function synchronize. After we used the function and used lh we found all the ktime? are same. When we display those waveform records processed by the function synchronize, we found the original start times are still kept.
      Could you tell me how to use the synchronize function effectively?
      Do you have another way to make all the records generated by the same earthquake have the same start time?
      Thanks in advance,
      Shutian   

      _______________________________________________
      sac-help mailing list
      sac-help<at>iris.washington.edu
      http://www.iris.washington.edu/mailman/listinfo/sac-help





    • Hi,

      You can change the time info in header with chnhdr.
      the SAC can change the relative time (in seconds) of the data.

      see the description part of the manual
      http://www.iris.edu/software/sac/commands/chnhdr.html

      Onur

      Dr. Onur TAN
      ---------------------------------------------- 40.7866N 29.4500E ---------
      TÜBİTAK Marmara Araştırma Merkezi, Yer ve Deniz Bilimleri Enstitüsü
      TUBITAK Marmara Research Center, Earth and Marine Sciences Institute
      Gebze - Kocaeli - TURKEY


      On 21.03.2011 15:47, "Shutian Ma" <shutian33<at>yahoo.ca> wrote:



      Dear colleagues,

      Recently we transferred some waveform records from IRIS. These records generated by the same earthquake do not have the same start time. As we need all the records generated by the same earthquake have the same start time to make measurement we tried to use sac2000 function synchronize. After we used the function and used lh we found all the ktime? are same. When we display those waveform records processed by the function synchronize, we found the original start times are still kept.
      Could you tell me how to use the synchronize function effectively?
      Do you have another way to make all the records generated by the same earthquake have the same start time?
      Thanks in advance,
      Shutian

      _______________________________________________
      sac-help mailing list
      sac-help<at>iris.washington.edu
      http://www.iris.washington.edu/mailman/listinfo/sac-help







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