What you will learn in Earthquakes and Seismology

1. 1. Strain, and the moment it fails

   Two plates slide past each other at a rate nobody chose, the fault between them is stuck, and the rock bends. The earthquake is the un-bending.

2. 2. Faults

   Three kinds of fault, and which one you get is decided by a single question: which of the three directions of squeezing happens to point straight down.

3. 3. Finding the epicentre

   Three seismograms, two arrivals on each, and the gap between them is a ruler. Then a fourth station arrives and the circles stop meeting at a point.

4. 4. Magnitude and intensity are different things

   One earthquake has one magnitude and hundreds of intensities. The ground under a building can matter more than how far it is from the epicentre.

5. 5. What one step up actually means

   Ten times the shaking and thirty-two times the energy, from the same single step. Spend an energy budget and find out what that costs.

6. 6. Tsunami

   A wave hundreds of kilometres long, half a metre high, crossing an ocean at the speed of an airliner — and its arrival time is one square root away.

7. 7. How often, and what "hundred-year" means

   Count a real catalogue and the points fall on a straight line. The line gives a rate, the rate is not a schedule, and no line gives a prediction.