Try Earthquake Lab free in your browser, with nothing to install and no account. Break a fault and watch the waves. Draw a fault on the map, choose how it moves, how deep it breaks and how big it is, and press Break: the fast P wave and the slower S wave spread out to three seismograph stations, and each pen writes its seismogram as they arrive. Then a quake is hidden. Mark where the P and S waves arrive, find the gap, read the distance on the travel-time chart, draw three circles with the compass, and mark the epicenter where they cross. The check says how close you were and which step to look at again.