Study Finds Nankai Trough Earthquake "Locked Zone" Changes Over Time

A Japanese research team has found that the "locked zone" within the expected source region of a future Nankai Trough earthquake shifts over time.

Researchers say changing tectonic plate locking along the Nankai Trough could improve earthquake forecasts.

The locked zone, where tectonic plates remain firmly stuck together until accumulated stress is released through earthquakes, is considered critical to understanding future megaquakes, Yurika Tarumi reported for Mainichi Japan.

The team, composed of researchers from the University of Tokyo's Institute of Industrial Science and the Japan Coast Guard, examined the Nankai Trough, where major earthquakes have occurred at intervals of roughly 100 to 200 years.

Researchers said the findings could improve forecasts of earthquake shaking and tsunami hazards by providing a more accurate picture of changing plate-locking conditions.

At the Nankai Trough, the Philippine Sea Plate is subducting beneath the Eurasian Plate at a rate of 4 to 6 centimeters per year.

The study, published in the international journal Earth, Planets and Space, analyzed crustal deformation data collected from both the seafloor and land between 2013 and 2023.

The researchers estimated the degree of plate locking by measuring how much slower the tectonic plates moved compared with their normal slip rate.

They found that some sections remained continuously locked, while others shifted over time.

The persistently locked region stretches from approximately 50 kilometers off the Bungo Channel to around 50 kilometers off the Tokai region, with especially strong locking observed offshore near Tosa City in Kochi Prefecture and the Kii Channel.

Meanwhile, the shifting locked zones were located across a broad area 50 to 100 kilometers offshore on the trench side of the continuously locked region.