Thread: Re: how to go from the recorded waveforms to SAC files

Started: 2023-03-21 15:23:53
Last activity: 2023-03-21 15:23:53
Topics: SAC Help

Hi Rui Zhou-

I don't see anything in the header relating to an event latitude or longitude or similar, so this must be just a time slice from this channel. It has a scale value which should be equal to the sensitivity of the instrument.

SAC> read 5B.1109..CHE.M.2016.299.001450.SAC
SAC> lh


FILE: 5B.1109..CHE.M.2016.299.001450.SAC - 1
----------------------------------------

NPTS = 824
B = 0.000000e+00
E = 3.292000e+00
IFTYPE = TIME SERIES FILE
LEVEN = TRUE
DELTA = 4.000000e-03
DEPMIN = -1.405000e+03
DEPMAX = 9.660000e+02
DEPMEN = -5.732281e+01
KZDATE = OCT 25 (299), 2016
KZTIME = 00:14:50.104
KINST = TCPH-20s
KSTNM = 1109
CMPAZ = 9.000000e+01
CMPINC = 9.000000e+01
STLA = 5.431783e+01
STLO = -1.172032e+02
STEL = 9.290000e+02
STDP = 5.000000e-01
LOVROK = TRUE
NVHDR = 6
SCALE = 1.195970e+09
LPSPOL = TRUE
LCALDA = TRUE
KCMPNM = CHE
KNETWK = 5B

You can convert miniSEED directly to SAC, but it won't contain the true ground motion values without making use of SAC's TRANSFER function coupled with a SAC PZ file containing this instrument's particular frequency response. You can get a SAC PZ file for this channel by using our web service:

http://service.iris.edu/irisws/sacpz/1/query?net=5B&sta=1109&loc=--&cha=CHE&starttime=2016-04-01&endtime=2016-12-01

As for use of the STA/LTA method, we (EarthScope formerly IRIS) do not employ that very much. Certainly not phase picking or event detection as that is not the job of a data center such as ours.

If you have specific questions about how to use SAC in your research, the SAC-HELP mailing list is a good place for it. There are experts here who can help.

Regards,

-Rob





On Mar 21, 2023, at 12:34 PM, Rui Zhou <zhourui2058<at>gmail.com> wrote:

Hi Rob:
Thank you very much for your reply.

I received data from https://ds.iris.edu/ds/nodes/dmc/forms/breqfast-request/ in miniseed format, then I converted the miniseed data into SAC files with mseed2sac software in Linux. I am a new user to IRIS and SAC software, the data I received MAYBE based on phase arrivals at stations from an earthquake based on the file name 5B.1109..CHE.M.2016.299.001450.SAC, I am not sure. I have attached the SAC file to this Email.

I talked to an experienced geophysicist, he said to go from miniseed to SAC file just needs format conversion. Could you please confirm if the experienced geophysicist was correct?

To ask my original question in another way: how did you obtain the miniseed files that we downloaded? The station MUST vibrate for many days from background noise AND earthquake events. Did you use the STA/LTA method to obtain the miniseed files from the station vibration? I would like to know all the details and specific steps. If it is processed by open-sourced software, I would like to know the specific computer codes that output the miniseed files.

Thank you.
Rui Zhou

On Wed, Mar 22, 2023 at 2:05 AM Rob Casey <rob.casey<at>earthscope.org <rob.casey<at>earthscope.org>> wrote:

Hi Rui Zhou-

Thank you for your interest. Am I correct that you received data from IRIS Web Services in SAC format? I am trying to understand the context of your question, as it sounds like it does not relate to the SAC software.

Since you mention the STA/LTA method, is the data you received based on phase arrivals at stations from an earthquake?

I look forward to hearing more about what process you are following.

Thanks,

-Rob



On Mar 21, 2023, at 8:52 AM, Rui Zhou (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu <sac-help-bounce<at>lists.ds.iris.edu>> wrote:

Hello Sir or Madam:
I am trying to use your SAC files. I often download miniseed files and convert them into SAC files. Please allow me to ask a basic question that I searched on your website but didn't find. A station that records seismic waveforms usually lasts for hours or days, could you please tell me how IRIS cut these waveforms into SAC files? A method I can think of is the STA/LTA method, could you please confirm if that is the method you utilized?
Thank you very much!
Rui Zhou

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<5B.1109..CHE.M.2016.299.001450.SAC>


04:52:48 v.f0c1234e