Labs / Geography
Seismic Waves Through Earth
Drag the earthquake around the rim and watch seismic waves race through the planet. Fast waves bend as they cross into the mantle and core, and the S waves vanish across a whole band of the surface — the shadow zone that first told geologists the outer core must be liquid.
t 0:00120° station —shadow —CMB 2891 km
What to try
- Switch to S waves only. Why do they never reach the far side of the planet, no matter where you put the quake?
- Now watch P waves. They pass right through the core — so why is there still a gap where no P wave lands?
- Slow the core speed far below the mantle speed. Does the shadow zone grow wider or narrower, and what does that tell you about how sharply rays bend at the boundary?
- The 120° station often reads “no direct arrival.” If you were a geologist in 1906 seeing that on every quake, what would you conclude about the inside of the Earth?
- Move the quake to different spots. Does the width of the shadow zone depend on where the earthquake happens, or only on what the Earth is made of?