‘Unusual’ Japanese quake leads to calls for a rethink on skyscraper designs and safety rules

Scientists studying the earthquake that struck southern Japan in April have identified a number of seismological factors that made the tremor so destructive – and warn that should the same factors combine beneath a major city it could bring down a ­skyscraper.

The 7.3 magnitude quake that struck beneath the city of Kumamoto on the evening of April 14 caused extensive damage, with hundreds of homes, buildings and other infrastructure collapsing from the violence of the shaking. Others were engulfed in landslides.

A total of 49 people were killed, and 100,000 people were evacuated from their homes. Many have been unable to return due to the damage or the threat posed to unstable buildings by the ongoing aftershocks.

A team at Tokyo’s Kogakuin University headed by Professor Yoshiaki Hisada has determined that a specific type of seismic movement took place in Kyushu and that the long-period ground movement was the most powerful ever observed during an inland quake caused by faults slipping.

“There are many different types of earthquake, but in the case of the Kyushu quake we have confirmed that a major fault – the Futagawa Fault – close to the surface slipped directly beneath ­Kumamoto City,” Hisada told The South China Morning Post.

When that was combined with long-period ground motion, “there can be severe damage, as we see in this case”, he said.

The residents of Kumamoto and surrounding districts were relatively fortunate that there
are few multi-storey structures in the city as the damage would have been far more extensive, the professor added.