Thread: Request for some clarifications

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following questions about pyweed (and jweed although no longer maintained):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