About deep earthquakes

Deep earthquakes were discovered in the 1920s, but they remain a subject of contention today. The reason is simple: they aren't supposed to happen. Yet they account for more than 20 percent of all earthquakes. Here's a new article with more basics about these remarkable seismic events.

And right on cue, a magnitude 6.9 earthquake occurred today 560 kilometers beneath Argentina, the last vestige of the Andean subduction zone. Visit the quake's USGS page and see the telltale seismic pattern of the descending plate, called a Wadati-Benioff zone, in the "historical seismicity" map.