The bolts holding up the ceiling that collapsed on 265 swimmers at a municipal pool here in Tuesday's earthquake had virtually no stabilizers, government investigators said Wednesday.
This means most of the bolts in the ceiling above the indoor swimming pool in Izumi Ward were prone to shaking, inspectors from the Land, Infrastructure and Transport Ministry said.
There were 265 people at the pool when the quake struck just before noon. One was seriously injured and 25 others sustained minor injuries.
The structure of the building itself is also vulnerable to shaking, the inspectors added.
The ceiling's construction was similar to the ceilings of gymnasiums in other parts of the country that collapsed in previous earthquakes, a trend that prompted authorities to notify local governments to boost earthquake-resistance.
Sendai officials said they acted on the notices, but the land ministry said it would continue probing to see whether there was something structurally wrong with the pool ceiling.