Researcher Likens Noto Earthquake to 1995 Hanshin Disaster; Seismic Waves Especially Damaging to Wood Buildings Observed

The Yomiuri Shimbun
People clear away parts of houses and other debris in Wajima, Ishikawa Prefecture, on Tuesday.

The Noto Peninsula Earthquake, which destroyed numerous buildings, likely involved a type of seismic wave that is known to strongly shake houses and other structures made of wood.

According to an analysis by Yuki Sakai, a professor of earthquake disaster prevention engineering at Kyoto University, a type of seismic wave that can destroy buildings was observed in Anamizu, Ishikawa Prefecture, and it was comparable in power to waves that caused extensive damage to buildings in the 1995 Great Hanshin Earthquake.

Seismic waves have various periods, indicating how long it takes for one complete cycle. Tremors are said to be more likely to be felt by human beings when the waves have short periods of less than one second.

Waves with a period of one to two seconds tend to cause the collapse of houses and other structures made of wood, and strong waves of this type were confirmed in some locations hit by the Noto earthquake, according to an analysis of data released by the National Research Institute for Earth Science and Disaster Prevention.

“In addition to the quake’s large scale, the soft ground in the region may have been a factor in the powerful shaking,” Sakai said.

In July last year, the government’s Earthquake Research Committee pointed out that the peninsula has soft ground and is prone to strong shaking.

Shintaro Yamasaki, an associate professor of engineering geology at Kyoto University, said urban areas on the peninsula where sand and other sediments have accumulated tend to be vulnerable to shaking and soil liquefaction.

The prolonged duration of the strong tremors is also believed to have contributed to the significant damage to wooden houses. Hiroyuki Goto, a professor of earthquake engineering at Kyoto University, estimated that strong shaking continued for about 20 seconds near the epicenter.

“Even buildings that didn’t collapse may have been damaged in unseen parts and sections. It’s very important to take precautions when entering a building,” Goto said.