The bangs, crackles and hums of Earth's seismic orchestra

Study gets to the bottom of 'musical symphony' produced in regions prone to mega-quakes as scientists work toward better quake hazard forecasting

You are at a classical music concert. There is an orchestra with three main sections. High up at the back, the percussion section has one very loud, large and moody-looking drum that gets struck very rarely. A handful of triangles produce occasional quieter "tings". Further down, in the middle, there is a small band of violinists, but they are playing the strings so slowly the audience can barely hear them. Down at the front, a family of double bass instruments produces low-pitched, gentler hums from time to time.

This somewhat unconventional orchestra is like a type of tectonic plate boundary known as a subduction zone. Subduction zones delineate the battle lines between the collision of two titanic tectonic plates. Yet, this encounter is rather one-sided. One plate firmly stands its ground; the other sinks into the depths of the Earth. The grinding and sliding of these two plates produces a musical concert that can be detected by sensitive geophysical instruments and by humans during large quakes. The shallow parts of subduction plate boundaries can produce devastating mega-earthquakes with magnitude eight or greater (like the giant drum in the percussion section). In the tens to hundreds of years between these massive quakes, scientists eagerly listen to the signals at subduction zones to estimate whether the plate boundary fault is primed for a future quake, and to forecast what a rupture may look like.