Thread: units of EVDP in SAC

Started: 2011-07-20 04:17:34
Last activity: 2011-07-22 15:25:16
Topics: SAC Help
Arthur Snoke
2011-07-20 04:17:34
To my knowledge, since IRIS/SAC v100, EVDP (focal depth in the SAC
header) has not been used in any SAC command. Please let me know if there
are commands I have overlooked.

Because of historical reasons, EVDP (focal depth) in SAC has the units
according to the SAC manual. RDSEED converts EVDP from kilometers (which
it is in blockette 71 in SEED) to meters when writing SAC waveforms.

For v101.5, the units of EVDP will be of interest because we will (re)
introduce a version of the TRAVELTIME command, in which for waveforms with
a defined location and origin time one can calculate arrival times for
body-wave phases using the iaspei-tau tables for either ak135 or iasp91
velocity models. For this command, the units of EVDP matter.

I personally would like to evolve towards having kilometers being the
default unit for EVDP. As a first step, kilometers would be the default
choice for EVDP in TRAVELTIME.

The point of this note is a canvass of the community to find if there are
any problems with using KM rather than M for EVDP. Let me know if there
are other programs that read SAC files and use EVDP assuming it is in
meters.

Arthur

  • Januka Attanayake
    2011-07-20 01:47:27
    Hello Arthur, 
    I use EVDP with taup_setsac to mark travel times in which case both units, meters and kilometers, are accommodated using different flags (evdp and evdpkm). If you are bringing in the same functionality with TRAVELTIME with km as the default unit, that would indeed be very helpful. However, I haven't come across a situation where I had to use meters instead of km. 

    Januka.
     
    _______________
    Serenity isn't freedom from the storm, but peace within the storm

    Januka Attanayake 
    Earthquake 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)

    Home page: http://sites.google.com/site/janukaattanayake/
    Research group: http://www.phys.uconn.edu/research/geophysics/index.html








    ________________________________
    From: Arthur Snoke <snoke<at>vt.edu>
    To: SAC-help Listserv <sac-help<at>iris.washington.edu>
    Sent: Tuesday, July 19, 2011 9:17 PM
    Subject: [SAC-HELP] units of EVDP in SAC

    To my knowledge, since IRIS/SAC v100, EVDP (focal depth in the SAC header) has not been used in any SAC command.  Please let me know if there are commands I have overlooked.

    Because of historical reasons, EVDP (focal depth) in SAC has the units according to the SAC manual.  RDSEED converts EVDP from kilometers (which it is in blockette 71 in SEED) to meters when writing SAC waveforms.

    For v101.5, the units of EVDP will be of interest because we will (re) introduce a version of the TRAVELTIME command, in which for waveforms with a defined location and origin time one can calculate arrival times for body-wave phases using the iaspei-tau tables for either ak135 or iasp91 velocity models.  For this command, the units of EVDP matter.

    I personally would like to evolve towards having kilometers being the default unit for EVDP.  As a first step, kilometers would be the default choice for EVDP in TRAVELTIME.

    The point of this note is a canvass of the community to find if there are any problems with using KM rather than M for EVDP.  Let me know if there are other programs that read SAC files and use EVDP assuming it is in meters.

    Arthur
    _______________________________________________
    sac-help mailing list
    sac-help<at>iris.washington.edu
    http://www.iris.washington.edu/mailman/listinfo/sac-help
  • George Helffrich
    2011-07-20 11:50:54
    MacSAC has a functioning version of the TRAVELTIME command.

    If the depth's numerical value is greater than 1000, it assumes the value is in meters. This is a useful heuristic for the Earth's earthquakes, but not perhaps for other terrestrial planets, e.g. the moon. (On the other hand, SAC's distance calculations, ellipticity corrections for distance and azimuth would be unsuitable for other planets.)

    My own view is that the heuristic works well enough that there isn't any need to change SAC's formal unit definition, though kilometers it is what earthquake seismologists expect.

    George Helffrich
    george.helffrich<at>bris.ac.uk



  • Arthur Snoke
    2011-07-20 14:05:23
    Comments on the two responses I got so far:

    1) Because traveltime did not work in SAC/IRIS, in the Help file for
    sss/traveltime
    http://www.iris.edu/software/sac/commands/sss.com/traveltime.html we
    recommend using taup_setsac. As with RDSEED, the default is meters for
    EVDP.

    2) I thought about some variant of George's macsac 1000 switch between
    meters and kilometers, but not having worked with very shallow events (of
    any kind) I was not sure where the threshold should be set. A 0 value is
    no problem, but does one use focal depths of 0.5 km? Patly because of my
    testing with traveltime, I am planning to changed the EVDP for fg/seismo
    to 15 km.

    On Tue, 19 Jul 2011, Arthur Snoke wrote:

    To my knowledge, since IRIS/SAC v100, EVDP (focal depth in the SAC
    header) has not been used in any SAC command. Please let me know if
    there are commands I have overlooked.

    Because of historical reasons, EVDP (focal depth) in SAC has the units
    according to the SAC manual. RDSEED converts EVDP from kilometers
    (which it is in blockette 71 in SEED) to meters when writing SAC
    waveforms.

    For v101.5, the units of EVDP will be of interest because we will (re)
    introduce a version of the TRAVELTIME command, in which for waveforms
    with a defined location and origin time one can calculate arrival times
    for body-wave phases using the iaspei-tau tables for either ak135 or
    iasp91 velocity models. For this command, the units of EVDP matter.

    I personally would like to evolve towards having kilometers being the
    default unit for EVDP. As a first step, kilometers would be the default
    choice for EVDP in TRAVELTIME.

    The point of this note is a canvass of the community to find if there are any
    problems with using KM rather than M for EVDP. Let me know if there are
    other programs that read SAC files and use EVDP assuming it is in meters.

    Arthur

    • Januka Attanayake
      2011-07-20 13:41:19
      Isn't EVDP for nuclear explosions is < 0.5 km ? I am not sure if there are any records of them in the IRIS DMS though. I suspect this is the reason why meters was used as the default unit to begin with? 
       
      _______________
      Serenity isn't freedom from the storm, but peace within the storm

      Januka Attanayake 
      Earthquake 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)

      Home page: http://sites.google.com/site/janukaattanayake/
      Research group: http://www.phys.uconn.edu/research/geophysics/index.html








      ________________________________
      From: Arthur Snoke <snoke<at>vt.edu>
      To: SAC-help Listserv <sac-help<at>iris.washington.edu>
      Sent: Wednesday, July 20, 2011 7:05 AM
      Subject: Re: [SAC-HELP] units of EVDP in SAC

      Comments on the two responses I got so far:

      1) Because traveltime did not work in SAC/IRIS, in the Help file for sss/traveltime http://www.iris.edu/software/sac/commands/sss.com/traveltime.html we recommend using taup_setsac.  As with RDSEED, the default is meters for EVDP.

      2) I thought about some variant of George's macsac 1000 switch between meters and kilometers, but not having worked with very shallow events (of any kind) I was not sure where the threshold should be set. A 0 value is no problem, but does one use focal depths of 0.5 km?  Patly because of my testing with traveltime, I am planning to changed the EVDP for fg/seismo to 15 km.

      On Tue, 19 Jul 2011, Arthur Snoke wrote:

      To my knowledge, since IRIS/SAC v100, EVDP (focal depth in the SAC header) has not been used in any SAC command.  Please let me know if there are commands I have overlooked.

      Because of historical reasons, EVDP (focal depth) in SAC has the units according to the SAC manual.  RDSEED converts EVDP from kilometers (which it is in blockette 71 in SEED) to meters when writing SAC waveforms.

      For v101.5, the units of EVDP will be of interest because we will (re) introduce a version of the TRAVELTIME command, in which for waveforms with a defined location and origin time one can calculate arrival times for body-wave phases using the iaspei-tau tables for either ak135 or iasp91 velocity models.  For this command, the units of EVDP matter.

      I personally would like to evolve towards having kilometers being the default unit for EVDP.  As a first step, kilometers would be the default choice for EVDP in TRAVELTIME.

      The point of this note is a canvass of the community to find if there are any problems with using KM rather than M for EVDP.  Let me know if there are other programs that read SAC files and use EVDP assuming it is in meters.

      Arthur
      _______________________________________________
      sac-help mailing list
      sac-help<at>iris.washington.edu
      http://www.iris.washington.edu/mailman/listinfo/sac-help
      • Renate Hartog
        2011-07-20 16:53:38
        We (Pacific Northwest) sometime have small local earthquakes for which our
        locator gives a depth < 1km. Explosions certainly can have depth < 1km. So,
        George's scheme could potentially go wrong for those. However, it might be a
        non-issue for him because the DMC doesn't keep track of small, local
        earthquakes, i.e. there won't be any event information in the SEED file.
        Larger ones probably always nucleate deeper than 1km.

        The easiest (least change) solution is to leave EVDP in m and provide an
        option to traveltime like Januka suggested. If the EVDP is a float field, it
        could be in km, as you could specify a shallow depth as, e.g., 0.255 km.
        Another thought is that with the advent of relative location algorithms,
        depth differences on the 10-s of m scale might be resolvable for clustered
        earthquakes and for that reason leaving the units stay "m" might be worth
        it.

        -Renate
        Pacific Northwest Seismic Network
        Seattle, WA

        On Wed, Jul 20, 2011 at 6:41 AM, Januka Attanayake <jattanayake<at>yahoo.com>wrote:

        Isn't EVDP for nuclear explosions is < 0.5 km ? I am not sure if there are
        any records of them in the IRIS DMS though. I suspect this is the reason why
        meters was used as the default unit to begin with?

        *_______________*
        *Serenity isn't freedom from the storm, but peace within the storm
        *
        *Januka Attanayake *
        *Earthquake 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)
        *
        Home page: http://sites.google.com/site/janukaattanayake/
        *Research group: http://www.phys.uconn.edu/research/geophysics/index.html
        *






        ------------------------------
        *From:* Arthur Snoke <snoke<at>vt.edu>
        *To:* SAC-help Listserv <sac-help<at>iris.washington.edu>
        *Sent:* Wednesday, July 20, 2011 7:05 AM
        *Subject:* Re: [SAC-HELP] units of EVDP in SAC

        Comments on the two responses I got so far:

        1) Because traveltime did not work in SAC/IRIS, in the Help file for
        sss/traveltime <
        http://www.iris.edu/software/sac/commands/sss.com/traveltime.html we
        recommend using taup_setsac. As with RDSEED, the default is meters for
        EVDP.

        2) I thought about some variant of George's macsac 1000 switch between
        meters and kilometers, but not having worked with very shallow events (of
        any kind) I was not sure where the threshold should be set. A 0 value is no
        problem, but does one use focal depths of 0.5 km? Patly because of my
        testing with traveltime, I am planning to changed the EVDP for fg/seismo to
        15 km.

        On Tue, 19 Jul 2011, Arthur Snoke wrote:

        To my knowledge, since IRIS/SAC v100, EVDP (focal depth in the SAC
        header) has not been used in any SAC command. Please let me know if there
        are commands I have overlooked.

        Because of historical reasons, EVDP (focal depth) in SAC has the units
        according to the SAC manual. RDSEED converts EVDP from kilometers (which it
        is in blockette 71 in SEED) to meters when writing SAC waveforms.

        For v101.5, the units of EVDP will be of interest because we will (re)
        introduce a version of the TRAVELTIME command, in which for waveforms with a
        defined location and origin time one can calculate arrival times for
        body-wave phases using the iaspei-tau tables for either ak135 or iasp91
        velocity models. For this command, the units of EVDP matter.

        I personally would like to evolve towards having kilometers being the
        default unit for EVDP. As a first step, kilometers would be the default
        choice for EVDP in TRAVELTIME.

        The point of this note is a canvass of the community to find if there are
        any problems with using KM rather than M for EVDP. Let me know if there are
        other programs that read SAC files and use EVDP assuming it is in meters.

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



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




        --
        Renate Hartog
        Research Scientist
        Pacific Northwest Seismic Network
        Department of Earth and Space Sciences
        University of Washington
        Box 351310
        Seattle, WA 98195

        Tel. +1-206-685-7079 (office)

        • Philip Crotwell
          2011-07-20 20:42:20
          This issue caused me quite a few headaches with TauP_SetSac.
          Ultimately I decided the best course of action was to do what the sac
          manual says, and so evdp is in meters. Of course a huge percentage of
          seismologists put the value in km. My personal bias is that if the sac
          spec says it is in meters, then any sac commands that use evdp should
          do so in meters, perhaps with a warning if the value looks like it
          might be kilometer, ie >1000. To change the meaning of a header at
          this point in sac's life seems like asking for more trouble and
          confusion.

          The best answer to this is to have the units in the header. But, one
          of the strengths of the sac file format is the simple header. One of
          the weaknesses of the sac file format is the simple header and so I
          doubt there is any place to put it.

          Philip

          On Wed, Jul 20, 2011 at 12:53 PM, Renate Hartog <jrhartog<at>uw.edu> wrote:
          We (Pacific Northwest) sometime have small local earthquakes for which our
          locator gives a depth < 1km. Explosions certainly can have depth < 1km. So,
          George's scheme could potentially go wrong for those. However, it might be a
          non-issue for him because the DMC doesn't keep track of small, local
          earthquakes, i.e. there won't be any event information in the SEED file.
          Larger ones probably always nucleate deeper than 1km.

          The easiest (least change) solution is to leave EVDP in m and provide an
          option to traveltime like Januka suggested. If the EVDP is a float field, it
          could be in km, as you could specify a shallow depth as, e.g., 0.255 km.
          Another thought is that with the advent of relative location algorithms,
          depth differences on the 10-s of m scale might be resolvable for clustered
          earthquakes and for that reason leaving the units stay "m" might be worth
          it.

          -Renate
          Pacific Northwest Seismic Network
          Seattle, WA

          On Wed, Jul 20, 2011 at 6:41 AM, Januka Attanayake <jattanayake<at>yahoo.com>
          wrote:

          Isn't EVDP for nuclear explosions is < 0.5 km ? I am not sure if there are
          any records of them in the IRIS DMS though. I suspect this is the reason why
          meters was used as the default unit to begin with?

          _______________
          Serenity isn't freedom from the storm, but peace within the storm
          Januka Attanayake
          Earthquake 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)
          Home page: http://sites.google.com/site/janukaattanayake/
          Research group: http://www.phys.uconn.edu/research/geophysics/index.html






          ________________________________
          From: Arthur Snoke <snoke<at>vt.edu>
          To: SAC-help Listserv <sac-help<at>iris.washington.edu>
          Sent: Wednesday, July 20, 2011 7:05 AM
          Subject: Re: [SAC-HELP] units of EVDP in SAC

          Comments on the two responses I got so far:

          1) Because traveltime did not work in SAC/IRIS, in the Help file for
          sss/traveltime
          http://www.iris.edu/software/sac/commands/sss.com/traveltime.html we
          recommend using taup_setsac.  As with RDSEED, the default is meters for
          EVDP.

          2) I thought about some variant of George's macsac 1000 switch between
          meters and kilometers, but not having worked with very shallow events (of
          any kind) I was not sure where the threshold should be set. A 0 value is no
          problem, but does one use focal depths of 0.5 km?  Patly because of my
          testing with traveltime, I am planning to changed the EVDP for fg/seismo to
          15 km.

          On Tue, 19 Jul 2011, Arthur Snoke wrote:

          To my knowledge, since IRIS/SAC v100, EVDP (focal depth in the SAC
          header) has not been used in any SAC command.  Please let me know if there
          are commands I have overlooked.

          Because of historical reasons, EVDP (focal depth) in SAC has the units
          according to the SAC manual.  RDSEED converts EVDP from kilometers (which it
          is in blockette 71 in SEED) to meters when writing SAC waveforms.

          For v101.5, the units of EVDP will be of interest because we will (re)
          introduce a version of the TRAVELTIME command, in which for waveforms with a
          defined location and origin time one can calculate arrival times for
          body-wave phases using the iaspei-tau tables for either ak135 or iasp91
          velocity models.  For this command, the units of EVDP matter.

          I personally would like to evolve towards having kilometers being the
          default unit for EVDP.  As a first step, kilometers would be the default
          choice for EVDP in TRAVELTIME.

          The point of this note is a canvass of the community to find if there
          are any problems with using KM rather than M for EVDP.  Let me know if there
          are other programs that read SAC files and use EVDP assuming it is in
          meters.

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



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




          --
          Renate Hartog
          Research Scientist
          Pacific Northwest Seismic Network
          Department of Earth and Space Sciences
          University of Washington
          Box 351310
          Seattle, WA 98195

          Tel. +1-206-685-7079 (office)


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




          • Arthur Snoke
            2011-07-20 22:52:50
            This exchange is exactly what I had hoped would happen. Thank you all.

            Attached is today's draft of the traveltime help file a a PDF. You can
            see my current thoughts. A couple of comments:

            1. Like Philip in his taup_setsac, I am allowing for either km or m for
            evdp. We differ in what the default is. If the input file has evdp in m
            -- and one knows it -- one can either change evdp to km using ch or
            evaluate before going into sss or one can use the depth-m command-line
            option (see second example).

            2. Note that we have a verbose option, which prints out phase times while
            still in sss. It also prints out the depth used.

            3. As seen in the second example, if one has not turned on the verbose
            option, the depth used is still printed out.

            4. If one does not change the evdp from meters to km, error messages will
            be produced that tells you the depth is too great.

            Arthur

            On Wed, 20 Jul 2011, Philip Crotwell wrote:

            This issue caused me quite a few headaches with TauP_SetSac.
            Ultimately I decided the best course of action was to do what the sac
            manual says, and so evdp is in meters. Of course a huge percentage of
            seismologists put the value in km. My personal bias is that if the sac
            spec says it is in meters, then any sac commands that use evdp should
            do so in meters, perhaps with a warning if the value looks like it
            might be kilometer, ie >1000. To change the meaning of a header at
            this point in sac's life seems like asking for more trouble and
            confusion.

            The best answer to this is to have the units in the header. But, one
            of the strengths of the sac file format is the simple header. One of
            the weaknesses of the sac file format is the simple header and so I
            doubt there is any place to put it.

            Philip

            On Wed, Jul 20, 2011 at 12:53 PM, Renate Hartog <jrhartog<at>uw.edu> wrote:
            We (Pacific Northwest) sometime have small local earthquakes for which our
            locator gives a depth < 1km. Explosions certainly can have depth < 1km. So,
            George's scheme could potentially go wrong for those. However, it might be a
            non-issue for him because the DMC doesn't keep track of small, local
            earthquakes, i.e. there won't be any event information in the SEED file.
            Larger ones probably always nucleate deeper than 1km.

            The easiest (least change) solution is to leave EVDP in m and provide an
            option to traveltime like Januka suggested. If the EVDP is a float field, it
            could be in km, as you could specify a shallow depth as, e.g., 0.255 km.
            Another thought is that with the advent of relative location algorithms,
            depth differences on the 10-s of m scale might be resolvable for clustered
            earthquakes and for that reason leaving the units stay "m" might be worth
            it.

            -Renate
            Pacific Northwest Seismic Network
            Seattle, WA

            On Wed, Jul 20, 2011 at 6:41 AM, Januka Attanayake <jattanayake<at>yahoo.com>
            wrote:

            Isn't EVDP for nuclear explosions is < 0.5 km ? I am not sure if there are
            any records of them in the IRIS DMS though. I suspect this is the reason why
            meters was used as the default unit to begin with?

            _______________
            Serenity isn't freedom from the storm, but peace within the storm
            Januka Attanayake
            Earthquake 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)
            Home page: http://sites.google.com/site/janukaattanayake/
            Research group: http://www.phys.uconn.edu/research/geophysics/index.html






            ________________________________
            From: Arthur Snoke <snoke<at>vt.edu>
            To: SAC-help Listserv <sac-help<at>iris.washington.edu>
            Sent: Wednesday, July 20, 2011 7:05 AM
            Subject: Re: [SAC-HELP] units of EVDP in SAC

            Comments on the two responses I got so far:

            1) Because traveltime did not work in SAC/IRIS, in the Help file for
            sss/traveltime
            http://www.iris.edu/software/sac/commands/sss.com/traveltime.html we
            recommend using taup_setsac.  As with RDSEED, the default is meters for
            EVDP.

            2) I thought about some variant of George's macsac 1000 switch between
            meters and kilometers, but not having worked with very shallow events (of
            any kind) I was not sure where the threshold should be set. A 0 value is no
            problem, but does one use focal depths of 0.5 km?  Patly because of my
            testing with traveltime, I am planning to changed the EVDP for fg/seismo to
            15 km.

            On Tue, 19 Jul 2011, Arthur Snoke wrote:

            To my knowledge, since IRIS/SAC v100, EVDP (focal depth in the SAC
            header) has not been used in any SAC command.  Please let me know if there
            are commands I have overlooked.

            Because of historical reasons, EVDP (focal depth) in SAC has the units
            according to the SAC manual.  RDSEED converts EVDP from kilometers (which it
            is in blockette 71 in SEED) to meters when writing SAC waveforms.

            For v101.5, the units of EVDP will be of interest because we will (re)
            introduce a version of the TRAVELTIME command, in which for waveforms with a
            defined location and origin time one can calculate arrival times for
            body-wave phases using the iaspei-tau tables for either ak135 or iasp91
            velocity models.  For this command, the units of EVDP matter.

            I personally would like to evolve towards having kilometers being the
            default unit for EVDP.  As a first step, kilometers would be the default
            choice for EVDP in TRAVELTIME.

            The point of this note is a canvass of the community to find if there
            are any problems with using KM rather than M for EVDP.  Let me know if there
            are other programs that read SAC files and use EVDP assuming it is in
            meters.

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



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




            --
            Renate Hartog
            Research Scientist
            Pacific Northwest Seismic Network
            Department of Earth and Space Sciences
            University of Washington
            Box 351310
            Seattle, WA 98195

            Tel. +1-206-685-7079 (office)


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



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

            Attachments
            • George Helffrich
              2011-07-22 02:11:33
              Dear All -

              Suggest the command line option be named DEPTH <d> {KM | M} like the syntax for FUNCGEN IMPSTRING <m> <n> {SECONDS | POINTS}.

              Opinion seems pretty much split on changing the EVDP definition.

              VERBOSE seems a good option for regional phases as well as core phases (lots of branch name suffixes).

              But chatty commands are a nuisance when you're processing hundreds of seismograms in a macro loop. Think again about *always* printing out the depth, or, if keen on that idea, add a TERSE option (as for RTREND).

              On 20 Jul 2011, at 20:52, Arthur Snoke wrote:

              This exchange is exactly what I had hoped would happen. Thank you all.

              Attached is today's draft of the traveltime help file a a PDF. You can see my current thoughts. A couple of comments:

              1. Like Philip in his taup_setsac, I am allowing for either km or m for evdp. We differ in what the default is. If the input file has evdp in m -- and one knows it -- one can either change evdp to km using ch or evaluate before going into sss or one can use the depth-m command-line option (see second example).

              2. Note that we have a verbose option, which prints out phase times while still in sss. It also prints out the depth used.

              3. As seen in the second example, if one has not turned on the verbose option, the depth used is still printed out.

              4. If one does not change the evdp from meters to km, error messages will be produced that tells you the depth is too great.

              Arthur

              On Wed, 20 Jul 2011, Philip Crotwell wrote:

              This issue caused me quite a few headaches with TauP_SetSac.
              Ultimately I decided the best course of action was to do what the sac
              manual says, and so evdp is in meters. Of course a huge percentage of
              seismologists put the value in km. My personal bias is that if the sac
              spec says it is in meters, then any sac commands that use evdp should
              do so in meters, perhaps with a warning if the value looks like it
              might be kilometer, ie >1000. To change the meaning of a header at
              this point in sac's life seems like asking for more trouble and
              confusion.

              The best answer to this is to have the units in the header. But, one
              of the strengths of the sac file format is the simple header. One of
              the weaknesses of the sac file format is the simple header and so I
              doubt there is any place to put it.

              Philip

              On Wed, Jul 20, 2011 at 12:53 PM, Renate Hartog <jrhartog<at>uw.edu> wrote:
              We (Pacific Northwest) sometime have small local earthquakes for which our
              locator gives a depth < 1km. Explosions certainly can have depth < 1km. So,
              George's scheme could potentially go wrong for those. However, it might be a
              non-issue for him because the DMC doesn't keep track of small, local
              earthquakes, i.e. there won't be any event information in the SEED file.
              Larger ones probably always nucleate deeper than 1km.

              The easiest (least change) solution is to leave EVDP in m and provide an
              option to traveltime like Januka suggested. If the EVDP is a float field, it
              could be in km, as you could specify a shallow depth as, e.g., 0.255 km.
              Another thought is that with the advent of relative location algorithms,
              depth differences on the 10-s of m scale might be resolvable for clustered
              earthquakes and for that reason leaving the units stay "m" might be worth
              it.

              -Renate
              Pacific Northwest Seismic Network
              Seattle, WA

              On Wed, Jul 20, 2011 at 6:41 AM, Januka Attanayake <jattanayake<at>yahoo.com>
              wrote:

              Isn't EVDP for nuclear explosions is < 0.5 km ? I am not sure if there are
              any records of them in the IRIS DMS though. I suspect this is the reason why
              meters was used as the default unit to begin with?

              _______________
              Serenity isn't freedom from the storm, but peace within the storm
              Januka Attanayake
              Earthquake 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)
              Home page: http://sites.google.com/site/janukaattanayake/
              Research group: http://www.phys.uconn.edu/research/geophysics/index.html






              ________________________________
              From: Arthur Snoke <snoke<at>vt.edu>
              To: SAC-help Listserv <sac-help<at>iris.washington.edu>
              Sent: Wednesday, July 20, 2011 7:05 AM
              Subject: Re: [SAC-HELP] units of EVDP in SAC

              Comments on the two responses I got so far:

              1) Because traveltime did not work in SAC/IRIS, in the Help file for
              sss/traveltime
              http://www.iris.edu/software/sac/commands/sss.com/traveltime.html we
              recommend using taup_setsac. As with RDSEED, the default is meters for
              EVDP.

              2) I thought about some variant of George's macsac 1000 switch between
              meters and kilometers, but not having worked with very shallow events (of
              any kind) I was not sure where the threshold should be set. A 0 value is no
              problem, but does one use focal depths of 0.5 km? Patly because of my
              testing with traveltime, I am planning to changed the EVDP for fg/seismo to
              15 km.

              On Tue, 19 Jul 2011, Arthur Snoke wrote:

              To my knowledge, since IRIS/SAC v100, EVDP (focal depth in the SAC
              header) has not been used in any SAC command. Please let me know if there
              are commands I have overlooked.

              Because of historical reasons, EVDP (focal depth) in SAC has the units
              according to the SAC manual. RDSEED converts EVDP from kilometers (which it
              is in blockette 71 in SEED) to meters when writing SAC waveforms.

              For v101.5, the units of EVDP will be of interest because we will (re)
              introduce a version of the TRAVELTIME command, in which for waveforms with a
              defined location and origin time one can calculate arrival times for
              body-wave phases using the iaspei-tau tables for either ak135 or iasp91
              velocity models. For this command, the units of EVDP matter.

              I personally would like to evolve towards having kilometers being the
              default unit for EVDP. As a first step, kilometers would be the default
              choice for EVDP in TRAVELTIME.

              The point of this note is a canvass of the community to find if there
              are any problems with using KM rather than M for EVDP. Let me know if there
              are other programs that read SAC files and use EVDP assuming it is in
              meters.

              Arthur
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              --
              Renate Hartog
              Research Scientist
              Pacific Northwest Seismic Network
              Department of Earth and Space Sciences
              University of Washington
              Box 351310
              Seattle, WA 98195

              Tel. +1-206-685-7079 (office)


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              <traveltime_july20.pdf>_______________________________________________
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              George Helffrich
              george.helffrich<at>bris.ac.uk



              • Arthur Snoke
                2011-07-22 03:34:01
                Suggest the command line option be named DEPTH <d> {KM | M} like the
                syntax for FUNCGEN IMPSTRING <m> <n> {SECONDS | POINTS}.

                If I know in advance that EVDP does not have the default units, both my
                suggested syntax for TRAVELTIME or Philip's taup routine have a mechanism
                for dealing with that. If I do not know the units, how would that option
                help?

                But chatty commands are a nuisance when you're processing hundreds of
                seismograms in a macro loop. Think again about *always* printing out
                the depth, or, if keen on that idea, add a TERSE option (as for RTREND).

                I have not used SSS in my work so am not sure how TRAVELTIME is used in
                conjunction with other commands. TRAVELTIME operates on all waveforms are
                in memory, so if one has read in 100 waveforms and does a sss ; traveltime
                depth-m, one gets only the depth line once. If one has a macro that
                processes one waveform at a time, a single output line per waveforms would
                indeed be there. I suppose if one wanted that, one could port the output
                to a file or to /dev/null.

                rtr terse works in MACSAC, but not in IRIS/SAC. Not a bad idea to have it
                in IRIS/SAC -- or just to leave out the printout as I have never found it
                very useful.

                • George Helffrich
                  2011-07-22 15:25:16
                  Dear All -

                  With the suggestion I'm trying to impose brevity and a syntactical uniformity on the way SAC's commands are expressed. DEPTH-M is kind of clunky to type. Given SAC's parsing primitives, a lone "KM" or "M" would achieve setting a default for retrieval of values from the header too. Perhaps I should have expressed the syntax as [DEPTH <d>] [{KM | M}] to make this more clear: you don't have to provide a DEPTH value to set a default.

                  On 22 Jul 2011, at 01:34, Arthur Snoke wrote:

                  Suggest the command line option be named DEPTH <d> {KM | M} like the syntax for FUNCGEN IMPSTRING <m> <n> {SECONDS | POINTS}.

                  If I know in advance that EVDP does not have the default units, both my suggested syntax for TRAVELTIME or Philip's taup routine have a mechanism for dealing with that. If I do not know the units, how would that option help?

                  George Helffrich
                  george.helffrich<at>bris.ac.uk



01:01:11 v.01697673