Jan. 1 quake caused liquefaction in wide areas, including dunes

A Japanese seismic engineering expert says damage from liquefaction in the New Year's Day earthquake was concentrated on sand dunes along the Sea of Japan coast, not just reclaimed land or former river courses.

Senna Shigeki, from the National Research Institute for Earth Science and Disaster Resilience, says liquefaction of sand dunes needs greater attention.

The magnitude 7.6 quake hit the Noto Peninsula in Ishikawa Prefecture and the surrounding areas of central Japan, leaving many people dead from fires, building collapses, tsunami, and the cold weather.

Damage from liquefaction, which causes soil to behave more like a liquid than a solid as a result of ground motion, also occurred in wide swathes of land, hindering the reconstruction of people's lives.

Senna used aerial photos as well as on-site inspections to analyze liquefaction damage from the latest jolt.

He says the phenomenon was observed in areas stretching about 320 kilometers east to west from Niigata City to Toyama and Ishikawa prefectures, and to Sakai City in Fukui Prefecture.

In Uozu City in Toyama, damage from liquefaction was found in areas that registered an intensity of 4 on the Japanese scale of zero to 7. Such damage has rarely been observed with that level of intensity.

Senna says liquefaction likely occurred there because the ground motion continued for a long time.

The researcher also points to geographical features of areas that suffered damage.
In the massive earthquake that hit northeastern Japan in March 2011, liquefaction caused major damage mainly on reclaimed land and former river courses.

But Senna says that in the latest quake, the damage was also observed in sand dunes, where wind-blown sand has accumulated.

He says damage was greater on the land side of the dunes, rather than the side facing the Sea of Japan, perhaps because fine sand particles from the sea side had accumulated there.

Senna says there are many sand hills on the Sea of Japan coast, where liquefaction was expected, but the issue did not draw much attention.

He suggests that measures to prevent further damage must be formulated for affected areas and those with similar geographical features.