Is it the tick of Earth’s heartbeat, or a ticking time bomb? Either way, instruments that monitor a 14-month pattern in seismic activity could serve as an super-early warning system for the “Really Big One,” the massive earthquake that’s expected to hit the Pacific Northwest sometime in the next few centuries.
The seismic ticks are known as episodic tremor and slow slip events, and they’ve been known about for more than a decade.
Such events are linked to the titanic clash between the Juan de Fuca tectonic plate and the North American plate, in a region known as the Cascadia subduction zone. The two plates grind into each other at a rate of an inch or two per year, about 25 miles below the surface.
