This earthquake, which caused damage to several roads and buildings, occurred along a strike-slip fault.
The exterior wall of a store that collapsed during an earthquake in Kumamoto, Japan, July 28, 2026.
JIJI Press/AFP via Getty Images
A magnitude 6.8 earthquake struck just south of the city of Kumamoto on Japan’s southern island of Kyushu on Tuesday afternoon, local time. The earthquake sparked fires and damaged roads and buildings, including a shopping center where rescuers are trying to extract trapped people.
The earthquake occurred along a disconnection faultwhere two sides of a fracture in the Earth’s crust slide past each other, located in what independent earthquake specialist Amilcar Carrera-Cevallos calls “one of the most seismically complex places in Japan.”
“Kyushu is at a real tectonic crossroads,” he says. On one side, the Philippine Sea Plate is sinking beneath the Eurasian Plate at a rate of about 40 to 50 millimeters (1.6 to two inches) per year. But on the other side, there is also a so-called back-arc basin which is disintegrating. “This stretch reaches central Kyushu and creates the Beppu-Shimabara graben, a rift zone riddled with active faults and volcanoes like Aso and Unzen,” explains Carrera-Cevallos. “So there’s a subduction pushing on one side and a rift pulling on the other, all crossed by a major strike-slip fault, the middle tectonic line.”
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The earthquake occurred in a local fracture within the crust of the Eurasian plate and was very shallow, about 10 kilometers (six miles) below the surface. This superficiality “explains in large part why the tremors reached Shindo level 7 – the highest level in Japan – and why buildings and bridges collapsed,” says Carrera-Cevallos. It was also right under a population center, says Allen Husker, a geophysicist at the California Institute of Technology. If the earthquake had occurred closer to the subduction trench, the damage would have been less severe.
This earthquake occurred along the same fault zone as a wave of deadly earthquakes in 2016. They were also strike-slip earthquakes and hit some of the same cities. “The big difference is what happens next,” says Carrera-Cevallos. “In 2016, a smaller [magnitude] A magnitude 6.2 earthquake struck first, then, about a day and a half later, a much larger earthquake struck. [magnitude] 7.0 struck close on a different foul. No one expected this second, larger earthquake.
Carrera-Cevallos said he was struck by the fact that it didn’t take a strong subduction earthquake to create the highest level of shaking and cause substantial damage. This creates a difficult problem in structural engineering that aims to deal with seismological risk. Local faults “are numerous [and] “This is a seismically mature and well-monitored region, but events like this remind us that even well-understood tectonic settings can still surprise us in their details.”
Additional reporting by Jackie Flynn Mogensen.
Editor’s Note (7/28/26): This story will be updated as new information becomes available.
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