The earliest scientists first observed the waves that earthquakes produce before they could accurately describe the nature of earthquakes or their fundamental causes, as discussed in Lessons 1–5.

They travel through the Earth in curved paths, but they change direction suddenly when they pass through the boundary between substances in different states. The diagrams show what happens when P ...

To figure out just where that earthquake happened, you need recordings from seismic stations in other places. While earthquake locations are normally done with a computer that can quickly determine ...