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.

Look at that mountain! Imagine you are standing at the base of a volcano looking up. You were told that the volcano isn’t going to erupt anytime soon, but you notice a little bit of smoke (or is that ...

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The top layer represents the location of the sound source and the path of sound propagation (A). The bottom layers represent convergence zones with different sound propagation paths (B-F). Sound waves ...