WIP: Add tutorial showing how to plot focal mechanisms (beachballs)

[yvonnefroehlich]

Description of proposed changes

This PR aims to add a tutorial showing how to plot focal mechanisms using pygmt.Figure.meca. It focuses on how the display of the beachballs can be adjusted and modified:

• Filling the quadrants
• Plotting the components of a seismic moment tensor
• Adjusting the outlines
• Highlighting the nodal planes
• Adding offset from the event location
• Adding a label
• Using size-coding and color-coding

Related PRs:

• Add aliases for L, T, and Fr : PR Figure.meca: Add aliases for "L", "T", and "Fr" #2546
• Expand docstring for scale: PR Figure.meca: Expand docstring for the scale parameter #2552
• Expand docstrings for compressionfill and offset: PR Figure.meca: Expand docstrings for "compressionfill", "cmap", and "offset" #2553

Preview: https://pygmt-dev--2550.org.readthedocs.build/en/2550/tutorials/advanced/focal_mechanisms.html

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.
• Use underscores (not hyphens) in names of Python files and directories.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash commands are:

• /format: automatically format and lint the code
• /test-gmt-dev: run full tests on the latest GMT development version

[yvonnefroehlich]

/format

[yvonnefroehlich]

So far this tutorial covers these aspects:

• Filling the quadrants
• Plotting the components of a seismic moment tensor (maybe to specific ?)
• Adjusting the outlines
• Highlighting the nodal planes
• Adding offset from the event location
• Adding a label
• Using size-coding and color-coding

It does not address details regarding allowed input formats and supported conventions.

Are there any other aspects people think are important to mention? If not, I will continue to improve and complete the comments and documentation 🙂.