A magnitude 7.1 earthquake struck Kumamoto Prefecture in southern Japan at 4:27 p.m. Tuesday (3:27 p.m. Philippine time), triggering the partial collapse of Mayuyama in Shimabara, Nagasaki — the same mountain whose catastrophic flank failure in 1792 caused Japan's deadliest volcanic disaster, killing roughly 15,000 people.
The Japan Meteorological Agency (JMA) placed the epicenter about five kilometers east of Uto City at a depth of approximately 10 kilometers. The United States Geological Survey independently measured the quake at magnitude 6.8.
Maximum Seismic Intensity Recorded in Uki City and Hikawa Town
The JMA recorded a maximum seismic intensity of 7 — the highest level on Japan's shindo scale — in Uki City and Hikawa Town. That rating indicates severe shaking capable of toppling reinforced structures, making movement on foot impossible, and triggering widespread infrastructure failure.
Prime Minister Sanae Takaichi confirmed injuries and reported fires, power outages, collapsed buildings, and damage to roads and bridges across the affected region.
Mayuyama's Eastern Slope Fails in Shimabara
Shimabara City confirmed through monitoring camera footage that the eastern, city-facing slope of Mayuyama partially collapsed shortly after the shaking began, according to Nagasaki broadcasters KTN and NBC. Firefighters on the ground observed the mountainside failing in real time, while video footage captured by residents showed debris streaming down the slope in white plumes as emergency alerts sounded across the city.
No injuries from the collapse had been reported as of Tuesday evening. Nagasaki Prefecture dispatched a disaster helicopter at 5:12 p.m. to survey the mountain from the air. Authorities said no abnormality was observed at the nearby Fugendake lava dome on Mount Unzen.
Mountain Had Shown Warning Signs Since April
Mayuyama's slope was already a documented concern before Tuesday's earthquake. Shimabara City had recorded surface peeling on the mountain following a strong earthquake in April, and that damage expanded during heavy rains in June — developments that prompted inspections by mountain specialists.
Tuesday's 7.1-magnitude event appears to have pushed the already-weakened slope past a critical threshold, though the full extent of the failure is still being assessed by authorities.
Over 150,000 Ordered to Evacuate Across Kumamoto
More than 150,000 people were instructed to move to evacuation centers following the quake, according to Prime Minister Takaichi's office. About 40,000 homes lost power across the affected zone.
NHK footage showed burning and collapsed structures, large cracks on an elevated highway, and a derailed freight train. Expressway overpasses in Yatsushiro sustained significant damage, and part of a bridge in the same city collapsed. Chipmaker TSMC evacuated workers from its plant in the area, while Sony said it was checking its facilities for damage.
Tsunami Warning Issued Then Lifted; Evacuation Shelters Opened
A tsunami warning of up to one meter was issued for the Ariake and Yatsushiro Seas but was subsequently lifted. In Nagasaki, Minamishimabara recorded a seismic intensity of 5-strong, issued a Level 4 evacuation order, and opened eight shelters. Shimabara City opened seven additional shelters for displaced residents.
JR Kyushu suspended conventional rail lines and the Nishi-Kyushu Shinkansen service in response to the disaster.
The 1792 Disaster That Tuesday's Quake Echoed
In May 1792, a series of earthquakes during Mount Unzen's eruption collapsed Mayuyama's flank into the Ariake Sea, sending a devastating tsunami into present-day Kumamoto. The disaster, remembered in Japan by the phrase "Shimabara erupted, Higo affected," killed around 15,000 people on both coasts and remains the deadliest volcanic-related event in Japanese history.
Tuesday's event reversed the geographic dynamic: rather than a Shimabara-side eruption shaking the mountain and sending a wave toward Kumamoto, it was a Kumamoto-side earthquake that rattled the same mountain across the bay.
JMA Links Epicenter to Area Near 2016 Hinagu Fault Zone
The JMA said the epicenter lies approximately 20 kilometers from the Hinagu fault zone, which produced the April 2016 Kumamoto earthquakes that killed more than 270 people. However, officials said it was too early to link Tuesday's event to that earlier seismic sequence.
The JMA warned residents in the region to expect strong aftershocks and elevated landslide risk for approximately one week following the main shock.
By the Numbers
- 7.1 — magnitude of the earthquake as measured by the JMA
- 6.8 — magnitude recorded by the United States Geological Survey
- 7 — maximum seismic intensity (highest on Japan's shindo scale) in Uki City and Hikawa Town
- 10 km — approximate depth of the earthquake's epicenter
- 150,000+ — people instructed to evacuate to centers
- 40,000 — homes that lost power
- 15,000 — people killed in the 1792 Mayuyama collapse disaster
- 270+ — people killed in the April 2016 Kumamoto earthquakes near the Hinagu fault zone
- 20 km — distance between Tuesday's epicenter and the Hinagu fault zone
- 5:12 p.m. — time Nagasaki Prefecture dispatched a disaster helicopter to survey Mayuyama
Why This Matters
Tuesday's earthquake is among the most powerful to strike the Kumamoto region since the deadly 2016 sequence, producing maximum shaking intensity at Japan's highest scale, triggering mass evacuations, and causing the partial collapse of a mountainside with a documented history of catastrophic failure. The partial failure of Mayuyama — already weakened by earlier seismic activity and rainfall — raises serious concerns about the stability of the remaining slope, with the JMA warning of continued landslide risk for up to a week. The event also underscores the persistent seismic hazard in southern Japan's Kyushu region, where historical fault zones remain active and densely populated urban and industrial areas, including facilities operated by TSMC and Sony, are directly exposed.
Photo credit: Photo courtesy of NHK/KTN Nagasaki via social media