TSMC's Kumamoto fab restarted within a day. So why is it still too early to call this over?

A day after the quake, TSMC's Japan fab, JASM, began returning to normal operation in stages. Structural safety of the buildings was confirmed first, and production is being brought back step by step, while the detailed equipment inspection and damage assessment are still under way. The second fab going up next door took no damage, though part of the construction work was paused because of aftershocks.

TSMC's Kumamoto fab moving back to normal operation in stages (ITmedia NEWS, 2026-07-29)

출처: itmedia.co.jp

Japan's Meteorological Agency, meanwhile, asked for about a week of caution against another quake of this size. Seismic activity is still elevated, and three more tremors have already been strong enough to shake objects off shelves, a lower 5 on Japan's intensity scale.

Kumamoto hit by intensity 7, activity still elevated, one week of caution urged (NHK, 2026-07-29)

출처: news.web.nhk

Why one week specifically

Ten years ago in this same Kumamoto, a strong quake at intensity 7 came first. People took it for the mainshock. Two days later a larger one, the real mainshock, hit. The first tremor had not been the main event but the leading edge of a bigger one, what seismologists call a foreshock. That is why the agency says this quake looks like the 2016 sequence.

Where this quake came from

Most earthquakes happen where one slab of the earth's crust grinds under another. That boundary is called a subduction zone, and the very large quakes tend to originate there. This one did not. It came from a crack inside Kyushu itself. A crack that can move again is called an active fault, and the one that moved here appears to be the Hinagu fault zone.

The Philippine Sea plate slides under the Eurasian plate here at four to six centimeters a year, loading that fault for centuries. Like a balloon that keeps taking air until it bursts, a fault that has been holding finally slips all at once, and that slip is the earthquake. This epicenter sits about 20 kilometers south of the 2016 epicenter. If the 2016 quake released the stress stored in the northern stretch of the fault, this one appears to have released the southern stretch.

What happened outside the fab

Twenty-eight sections of stone wall collapsed at Kumamoto Castle. Ten people are unaccounted for after a gas leak at an Aeon mall. At a paper plant in Yatsushiro, two people were found in cardiac arrest and nine are missing. Kikuyo Town holds JASM's two fabs along with Sony and Fujifilm facilities inside the same 20-kilometer radius. One plant holding up is not the same as the region holding up.

So what actually settles this

It comes down to one question. Was this the end of it, or the leading edge of something larger the way 2016 was. If no bigger quake arrives within the week and the aftershocks fade, JASM's staged restart holds. If another quake of this size or larger hits, everything resets: the building checks that looked finished, the detailed equipment inspection, the restart schedule. When a fab stops and starts repeatedly, the loss does not scale with downtime alone. Each restart drags the inspection and requalification steps along with it again.