Sensors placed in the borehole could detect changes in strain, tilt and pressure in the ground miles below the surface. "That will be a great advantage in giving us a few days or hours warning before something happens. Current warning systems in Japan only warn us 10 minutes before a large earthquake strikes. We need real-time data from the exact point."

Detect shifts in the mantle, and the resulting earthquakes with... a big shaft down into the mantle?