Unruptured fault from 2016 likely behind powerful Japan temblor: Experts

A powerful magnitude 7.1 earthquake that struck southwestern Japan on July 28 is likely the result of a fault that remained unruptured during twin temblors a decade ago, experts suggest. They are also warning that significant seismic activity may persist in the region.

The epicenter of the recent quake in Kumamoto Prefecture was geographically close to the locations of two major earthquakes in April 2016 – a magnitude 6.5 on April 14 and a magnitude 7.3 two days later. All three seismic events registered the maximum 7 on Japan's seismic intensity scale in parts of Kumamoto.

The 2016 earthquakes caused widespread devastation, resulting in over 270 fatalities and significant damage to the region. Experts have long noted that the southern portion of the Hinagu fault zone, a major fault line running through central Kyushu, remained largely intact after the 2016 events.

Shinji Toda, a seismology professor at Tohoku University, analyzed seismic activity near the Hinagu fault zone over the past decade. His findings indicate that the number of temblors measuring magnitude 1.5 or greater has more than doubled since before the 2016 quakes. Toda believes the 2016 earthquake generated substantial strain and stress, leading to the movement along the Hinagu fault zone observed in the recent quake, suggesting a shared underlying mechanism.

The Japan Meteorological Agency reported that the July 28 quake occurred at a depth of 16 kilometers and along a "strike-slip" fault. This type of fault involves horizontal movement of adjacent areas against each other, similar to the mechanism observed in the 2016 temblors.

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It is believed that the 2016 earthquake caused a significant strain and stress, resulting in movements along part of the Hinagu fault zone this time.