Journal Highlights

The Curious Case of the Ultradeep 2015 Ogasawara Earthquake

Research Spotlight—

Unusual ground motion associated with the deepest major earthquake in the seismological record is due to both its great depth and its origin away from the subducting slab.

On 30 May 2015, a powerful earthquake struck west of Japan’s remote Ogasawara (Bonin) island chain, which lies more than 800 kilometers south of Tokyo. Although it caused little damage, the magnitude 7.9 quake was noteworthy for being the deepest major earthquake ever recorded—it occurred more than 100 kilometers below any previously observed seismicity along the subducting Pacific Plate—and the first earthquake felt in every Japanese prefecture since observations began in 1884.

The 680-kilometer-deep earthquake was also notable for its unusual ground motion. Instead of producing a band of high-frequency (>1 hertz) seismic waves concentrated along northern Japan’s east coast, as is typical for deep subduction-related earthquakes in this region, this event generated strong, low-frequency waves that jolted a broad area up to 2,000 kilometers from the epicenter. To explain this uncharacteristic wavefield, Furumura and Kennett analyzed ground motion records from across the country and compared the results to observations from a much shallower, magnitude 6.8 earthquake that occurred within the Pacific slab in the same area in 2010....more

-- Terri Cook, Freelance Writer,