Plot earthquakes between specific concentric circles using equidistant projection

Q&A
1

Hi, I am new to GMT. I have plotted earthquakes data using azimuthal equidistant projection. My code and plotted map are;
Code:

Code.dat (562 Bytes)
Earthquakes data:
earthquakes.dat (412.2 KB)
Plotted map:
Map

My query is;

  1. How to plot earthquakes data only between concentric circles of 70, 140 degrees as shown in blue colour on plotted map considering (centerN, centerE) values?

Kindly help me. Thanks.

2

Several possible ways I think:

  1. Use mapproject -G<lon/lat>+ud to compute distance in degrees from your center, then use gmtselect -Z to only pass those in your 70-140 range to plot.
  2. Lay down a clip path so that you only see the ones you want in that donut. This means making a polygon in geographical coordinates or work with Cartesian circles given you map size.

I would do option 1 I think.

3

Thanks for help. I have plotted map using option 1, which you mentioned. The commands which I used are below, have a look on these commands to see these are correct.
commands:

  1. calculate distance in degrees from center
    gmt mapproject earthquakes(lon,lat) -G$centerE/$centerN+ud > earthquakes_distance_degrees
  2. plot earthquakes only between 70-140 degrees
    gmt select earthquakes_distance_degrees -Z70/140 | gmt psxy -Rg -JE -Sc0.16c -Gbrown > Map

Apart from this, I want to label my map as in attached image.
13.3.6.2.From_paper_13.3.6.1

My query is how to draw lines from center to outer frame circle (black lines) and label these lines at outer frame with values (0,60,120…) degrees. What way/commands can be use to do this task. Kindly help.

4

Well, would it not just be an layer of basemap using basic polar (cylindrical) projection -JP?

5

Hi, I have plotted the map with labels of outer circle using (JP) projection. Following way used to get it;
gmt psbasemap -Rg -JP5i+a -B30g30 --FORMAT_GEO_MAP=+ddd
map:

Test
Test1619×1620 87.9 KB

" Now adding above layer to the first map of this post:
gmt begin Map png
centerE=141
centerN=39
gmt psbasemap -Rg -JP5i+a -B30g30 --FORMAT_GEO_MAP=+ddd
gmt pscoast -Rg -JE141/39/170/5i -A100000 -Gdarkgrey -Swhite
gmt psxy -Rg -JE -SE- -W0.6p,blue << EOF
$centerE $centerN 15540
$centerE $centerN 31080
EOF
gmt end show

Output map:

Map2
Map21619×1620 111 KB

I think the way which I used above for adding outer frame with label is correct?

Now how to draw lines from map center (centerE=141, centerN=39) to the outer circle frame annotation points (0-330). Thanks.

6

Please, wrap your code in triple backticks ```