[SAC-HELP] units of EVDP in SAC

Januka Attanayake jattanayake at yahoo.com
Wed Jul 20 06:41:19 PDT 2011


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? 
 
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Januka Attanayake 
Earthquake Seismology & Economics
The University of Connecticut 
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________________________________
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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