Over the last ten days scientists at Oregon State University [Hatfield Marine Science Center] have recorded more than 600 earthquakes emanating from offshore, several of which registered 5.0 or higher. The puzzling aspect of this quake swarm is that they’re not located at the edge of the region’s tectonic plate boundaries, but in the middle of the Juan de Fuca plate itself.

Using hydrophones left over from submarine surveillance during the Cold War, the researchers admit they do not understand what’s happening to cause this seismic activity. The quakes originate about 150 nautical miles southwest of Newport, Oregon in a basin between two subsurface faults where previous earthquake clusters have been recorded.

As magma gets injected into the crust to push the plates apart, quake swarms are fairly common and sometimes lava breaks through onto the sea floor. What sort of tectonic process is causing this swarm in the middle of the plate is unknown, but researchers will be keeping a close eye on it in hopes of finding out.

Links:
Unusual Earthquake Swarm off Oregon
2006 Mexican Tectonic Plate Motion Reversal