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.<br>
<br>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.<br>
<br>-Renate<br>Pacific Northwest Seismic Network<br>Seattle, WA<br><br><div class="gmail_quote">On Wed, Jul 20, 2011 at 6:41 AM, Januka Attanayake <span dir="ltr"><<a href="mailto:jattanayake@yahoo.com">jattanayake@yahoo.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-family: arial,helvetica,sans-serif; font-size: 10pt;">
<div><span>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? </span></div>
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<font face="'bookman old style', 'new york', times, serif" size="1"><b>Januka Attanayake </b></font></div> <div style="color: rgb(162, 162, 162);"><font face="'bookman old style', 'new york', times, serif" size="1"><b>Earthquake Seismology & Economics<br>
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<font face="Arial" size="2"><div class="im"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Arthur Snoke <<a href="mailto:snoke@vt.edu" target="_blank">snoke@vt.edu</a>><br></div><b><span style="font-weight: bold;">To:</span></b> SAC-help Listserv <<a href="mailto:sac-help@iris.washington.edu" target="_blank">sac-help@iris.washington.edu</a>><br>
<b><span style="font-weight: bold;">Sent:</span></b> Wednesday, July 20, 2011 7:05 AM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [SAC-HELP] units of EVDP in SAC<br></font><div><div></div><div class="h5">
<br>Comments on the
two responses I got so far:<br><br>1) Because traveltime did not work in SAC/IRIS, in the Help file for sss/traveltime <<a href="http://www.iris.edu/software/sac/commands/sss.com/traveltime.html" target="_blank">http://www.iris.edu/software/sac/commands/sss.com/traveltime.html</a>> we recommend using taup_setsac. As with RDSEED, the default is meters for EVDP.<br>
<br>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.<br>
<br>On Tue, 19 Jul 2011, Arthur Snoke wrote:<br><br>> 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.<br>> <br>> 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.<br>
> <br>> 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.<br>
> <br>> 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.<br>> <br>> 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.<br>> <br>> Arthur<br>_______________________________________________<br>sac-help mailing list<br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>Renate Hartog<br>Research Scientist<br>Pacific Northwest Seismic Network<br>Department of Earth and Space Sciences<br>University of Washington<br>Box 351310<br>Seattle, WA 98195<br>
<br>Tel. +1-206-685-7079 (office)<br><br>