[SAC-HELP] units of EVDP in SAC
George Helffrich
george.helffrich at bristol.ac.uk
Thu Jul 21 11:11:33 PDT 2011
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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>>>>
>>>>
>>>>
>>>> _______________________________________________
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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)
>>>
>>>
>>> _______________________________________________
>>> sac-help mailing list
>>> sac-help at iris.washington.edu
>>> http://www.iris.washington.edu/mailman/listinfo/sac-help
>>>
>>>
>>
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> <traveltime_july20.pdf>_______________________________________________
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George Helffrich
george.helffrich at bris.ac.uk
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