What causes earthquakes? A geologist explains where they're most common and why

Earthquakes accompany both subduction and rifting. In fact, that is how the plate boundaries were first discovered. In the 1950s, when a global seismic network was established to monitor nuclear tests, geophysicists noticed that most earthquakes occur along relatively narrow bands that either fringe the edges of ocean basins, as in the Pacific, or cut right down the middle of basins, as in the Atlantic.