Lab 04

Earthquakes do not happen just anywhere

Plot the biggest earthquakes ever recorded on a blank map and they do not scatter. They draw a set of lines — and those lines are the edges of about fifteen rigid slabs of rock floating on a mantle that flows. The previous lab took a probe down through those layers; this one stays at the top and asks what they do to the surface. Turn the earthquakes on first, then turn the boundaries on, and watch them meet.

Click a plate, a boundary, an earthquake or a volcano

The map
Start here
Cross-section

Three things two plates can do at a shared edge

Pull apart, push together, or slide past. Every trench, every mountain range and every volcanic island on the map above is one of these five arrangements, repeated. The drawings are schematic — the vertical scale is exaggerated several times over — but the numbers on them are measured.

Boundary
250 million years

Run it backwards and the Atlantic closes

At a few centimetres a year nothing appears to happen. Over 250 million years it adds up to a different planet. Drag the slider from Pangaea to today and on into the future.

250million years ago

What you are looking at: schematic reconstructions, not survey data. The continent outlines are their present-day shapes, moved and rotated along smooth paths between a handful of hand-set positions so the story reads correctly. Real palaeogeographic models also stretch and break the continents, and they disagree with each other by hundreds of kilometres before about 200 million years ago.

Reference

How anyone worked this out