I want to give symbols to my earthquake data like size to magnitude and color to depth but im unable can someone help me

Q&A PyGMT Q&A
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1

filtered_data_gmt.txt (100.0 KB)
this is the file.

import numpy as np
import pygmt


fig = pygmt.Figure()

# CPT (adjust to your depth/magnitude range if needed)
pygmt.makecpt(cmap="red,green,blue", series="0/300/10", output="quakes.cpt")

# --------------------
# 1) MAP PANEL
# --------------------
fig.coast(
    region=[127.6, 134.4, 30, 34.4],
    projection="M4i",
    frame=["xa1g1", "ya1g1", '+t"Kyushu"'],
    land="lightbrown",
    shorelines="0.25p",
)

fig.basemap(
    map_scale="jBR+w200k+o0.5c/0.5c+f"
)

fig.plot(
    data="filtered_data_gmt.txt",
    style="c0.15c",
    pen="faint",
    cmap="quakes.cpt",
)

# --------------------
# 2) AUTO PROFILE LINE (PCA, NO EXTENSION) + PROJECT
# --------------------
xy = np.loadtxt("filtered_data_gmt.txt", usecols=(0, 1), skiprows=1)

lon = xy[:, 0]
lat = xy[:, 1]

X = np.column_stack([lon, lat])
X0 = X - X.mean(axis=0)

C = np.cov(X0.T)
eigvals, eigvecs = np.linalg.eig(C)
v = eigvecs[:, np.argmax(eigvals)]

# Keep direction consistent
if v[0] < 0:
    v = -v

t = X0 @ v
tmin, tmax = t.min(), t.max()

# A and B exactly at data limits (NO extension)
A = X.mean(axis=0) + tmin * v
B = X.mean(axis=0) + tmax * v

# Plot the profile line in BLACK
fig.plot(
    x=[A[0], B[0]],
    y=[A[1], B[1]],
    pen="2p,black",
)

# Project earthquakes onto the profile
pygmt.project(
    data="filtered_data_gmt.txt",
    unit=True,
    center=[float(A[0]), float(A[1])],
    endpoint=[float(B[0]), float(B[1])],
    convention="pz",
    width=[-100, 100],
    outfile="cross.dat",
    output_type="file",
)

# --------------------
# 3) CROSS-SECTION PANEL
# --------------------
fig.shift_origin(yshift="-8c")

fig.basemap(
    projection="X10c/-6c",
    region=[0, 80, 0, 50],
    frame=[
        'xafg10+l"Distance (km)"',
        'yafg10+l"Depth (km)"',
        "WSen",
    ],
)

fig.plot(
    data="cross.dat",
    style="c0.2c",
    pen="0.5p,black",
    fill="red",
)

# --------------------
# 4) OUTPUT
# --------------------
fig.savefig("kyushu_cross_section.pdf")
fig.show()
2

Hi @parbuss2-hue,

I just formatted your script as code. You can do this by placing three backticks in the line before and after the block with the script:

```
your script formatted as code
```

For the size coding (magnitude):
If you want to use a quantity, there should be no size given via the style parameter: style=c0.15c → style="cc". Probably you need to scale the magnitude values before plotting.

For the color coding (depth):
Based on your data, all earthquakes are shallower than 20 km. Your colormap covers the range 0-300 km using three different colors. So all points are plotted in the first color, in your case red.

3

im using GMT for first time in my life during my internship and i have windows will you help me adjusting my code ? will you add it in my code ?

4

Try what everyone is doing these days. Ask an LLM (I strongly advise using Claude.ai) to write you the script. Be specific on the things you want in your figure.

5

@parbuss2-hue, I agree learning GMT can be overwhelming at the beginning, but with the Python (and Julia) wrappers, things get much easier.

Besides asking a LLM to write you the script (I guess you got the script and should adjust it for your task and data), you can go the old-school way: The PyGMT tutorial Plotting data points — PyGMT explains how to create the type of map you want.