Shear wave splitting

Q&A
1

I am trying to plot my shear-wave splitting parameters on GMT by using psxy, but I misunderstood something .
if legend is
45.50 54.50 30 1.0
I expected to have a line with an azimuth of 30 degrees from the vertical, but it seems I have more a line with an azimuth of 60 degrees from the vertical. I am not sure what is wrong with my pixy

gmt psxy legend -R$R -Sv0.2i+jc -W2.5p,red -X-0.05 -Y0.1

Thanks
Walid

2

use -SV (capital V) to get azimuth CW from North instead of angle CCW from East (-Sv), and I also suggest to use -SVB to get the stick/vector balanced on the center point, rather than pointing away from it, because splitting “fast axes” are orientational (0…180 deg) rather than directional (0…360 deg)

1 Like
3

Hi!
I’m new to the community and I apologize if this is not the right place to ask this question.

I am trying to do the same (plot azimuth lines from SWS analysis), however, I cannot find a way to plot the lines balanced at the center point using -SVB or -SVb as specified in the documentation. Lines seem to start from the midpoint (event location).
This is the line I am using:
gmt psxy -R -J stationX.dat -SVB0c -Wthinner,limegreen -l"Events"+f15p -B > azimuth0.ps

Thank you very much!

4

Am not sure about your problem …

Are -R (region) and -J (projection) are defined ? It seems you’re creating a new .ps file (>)
Can you give a few lines of stationX.dat ?

5

Yes, -R and -J are defined: -R-104.65/-103.95/31.5/31.85 -JM10c
Here are a few lines of the .dat file:
-104.3 31.65 81.308 0.49388
-104.29 31.661 157.13 0.58367
-104.31 31.654 101.05 0.18367
-104.3 31.659 73.23 0.53265
-104.31 31.66 88.205 0.61224
-104.2 31.653 63.339 0.69388

Thank you!!

6

Have you looked at vectors attributes ?

7

Well, I just tool a look again and I definetely missed this:

In addition, all but circular vectors may take these modifiers:

+j just determines how the input x,y point relates to the vector. Choose from beginning [default], end, or center.

So my line now looks like:

gmt psxy -R-104.65/-103.95/31.5/31.85 -JM10c stationX.dat -SVB0c+jc -Wthinner,limegreen -l"Events"+f15p -B

and it works. However, I do get this Warning: 0c+j not a valid number and may not be decoded properly.

Thank you very much!

8

I’ll have a look at that. I think we check if the header size is > 0 but if no header (+b or +e) are requested one should be able to not give on or give 0.

9

You are mixing old GMT 4 syntax (B) with GMT 6 syntax (+jc) and the parser sees it as an old-GMT4 syntax and you get this (harmless) warning. I suggest you use GMT 6 syntax going forward, which in your case would be -SV0+s+jc.

10

Got it! This worked indeed, thank you very much!