Thread: Request for some clarifications

Started: 2023-06-30 22:48:48
Last activity: 2023-07-03 09:59:25
Topics: PyWEED Help
Appiah, Nicholas
2023-06-30 22:48:48
Hello,

I am Nicholas Appiah and a graduate student in Geophysics at Texas Tech University. I would be grateful if I could get some clarifications on the following questions about pyweed (and jweed although no longer maintained):

1. For pweed's BH? data, I know the first two channels are horizontal. But which channel is North-South, and which is East-West? I often have these two mixed up. And is the same as jweed?
2. I compared jweed data with pyweed data and I realized azimuths and back azimuths are reversed. pyweed's azimuth is jweed's back azimuth and vice versa. What possible reason can we ascribe to this reversal, and which is correct?

Looking forward to your response.

Nicholas

Nicholas Appiah
PhD Student / Teaching Assistant
Department of Geosciences
Texas Tech University
Science, Rm. 126A
Lubbock, TX 79409-1053

  • Adam Clark
    2023-07-03 09:59:25
    Hello Nicholas,

    1. Usually the North/South channel will be labeled BHN and the East/West
    channel will be labeled BHE. In some cases you will find BH1 and BH2
    instead -- usually this means that the instruments are not aligned along
    cardinal directions, but this is only a convention so the only way to be
    sure is to look at the detailed instrument metadata. I see that this isn't
    displayed in PyWEED, which seems like a useful feature to have. For now,
    the easiest option is to look these up in a tool like MDA, eg.
    https://ds.iris.edu/mda/CU/ANWB/00/BH1/ Here you can see that the azimuth
    for the channel is 223 (where 0 is North). The other horizontal component
    should almost always be 90 degrees from this, so
    https://ds.iris.edu/mda/CU/ANWB/00/BH2/ is at 313.

    2. Are these the azimuth/back-azimuth in the data output (eg. SAC)? PyWEED
    uses the ObsPy library for this, so I would suspect that is the correct
    value. Please let me know if this was from a different context.

    Cheers,
    Adam



    On Mon, Jul 3, 2023 at 9:24 AM Appiah, Nicholas (via IRIS) <
    pyweed-help-bounce<at>lists.ds.iris.edu> wrote:

    Hello,

    I am Nicholas Appiah and a graduate student in Geophysics at Texas Tech
    University. I would be grateful if I could get some clarifications on the
    following questions about pyweed (and jweed although no longer maintained):

    1. For pweed's BH? data, I know the first two channels are horizontal.
    But which channel is North-South, and which is East-West? I often have
    these two mixed up. And is the same as jweed?
    2. I compared jweed data with pyweed data and I realized azimuths and
    back azimuths are reversed. pyweed's azimuth is jweed's back azimuth and
    vice versa. What possible reason can we ascribe to this reversal, and which
    is correct?

    Looking forward to your response.

    Nicholas

    *Nicholas Appiah*
    PhD Student / Teaching Assistant
    Department of Geosciences
    Texas Tech University
    Science, Rm. 126A
    Lubbock, TX 79409-1053

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    Adam Clark
    adam.clark<at>earthscope.org
    https://www.earthscope.org

16:43:10 v.01697673