Week 6 lab, the seismic wavefields chapter, and Exercises 4a and 4b

[ARS183]

Eleven commits covering the Week 6 computer lab, the reproduction of chapter 5 of the lecture notes, and Exercises 4a and 4b.

What is in it

Week 6 lab, 3_diffusion_fields/labs/week06_em_diffusion.md
Chapter 4, mechanical waves, a new section on solutions to the wave equation
Exercises 4a and 4b
21.5 MB of new binary data, the sixteen .npz gathers at about 1.34 MB each, plus two short MP4s at 0.39 and 0.49 MB. The gathers were recompressed from the originals to float32 with deflate and verified value-identical.

Footprint on shared files

_toc.yml gains five lines. _config.yml and requirements.txt are untouched: ipympl and plotly are micropip-installed at run time, since the build never executes these pages.

They use the ipympl backend, so hovering a figure reports the position and the amplitude under the mouse. Exercise 4b needs that: students read velocities, a cross-over distance and an apex time straight off the gather. It works under Live Code with no change to the book's configuration.