The Nankai subduction zone hugs the southeastern curve of Japan and is one of the most seismologically active regions on the planet. The combination of the region's short seismic cycle—great earthquakes (magnitude 8 or greater) occurring roughly every 100–150 years—and its superb history of geophysical observations makes it an attractive natural observatory for scientists looking to study the evolution of subduction zones during and between great earthquakes. The last major quakes in the region occurred in the mid-1940s, and the decades since have offered opportunities for researchers to pursue innovative geodetic monitoring and modeling.