Noto Quake’s Acceleration Measurements Rival 3/11 Temblor; Readings Of 1,000 Gal or More Seen Over Unusually Wide Area

The Yomiuri Shimbun
A road that collapsed due to Monday’s earthquake in the town of Shika, Ishikawa Prefecture, is seen on Tuesday.

In one aspect, the magnitude 7.6 earthquake that struck Ishikawa Prefecture’s Noto region on Monday was nearly as powerful as the 2011 Great East Japan Earthquake, with the latest one measuring a maximum of 2,828 gals, scientists said. A gal is a unit of acceleration related to the intensity of the ground’s shaking.

Seven observation points on the Noto Peninsula recorded at least 1,000 gals — a benchmark for deeming a temblor a “major earthquake” — and the data indicates that Monday’s shaking was extremely strong over a wide area.

According to a report by the National Research Institute for Earth Science and Disaster Resilience (NIED), an observation point in the town of Shika recorded 2,828 gals, which is close to the figure measured in the Great East Japan Earthquake at 2,933 gals, while 1,000 gals or more were measured in the cities of Wajima and Suzu, the town of Anamizu and elsewhere.

Acceleration as measured in gals is one of the indicators used in standards for earthquake-resistant design of buildings.

“Maximum acceleration is not the only indicator to measure the strength of a quake, but it is extremely rare for an earthquake to exceed 1,000 gals over such a wide area,” said Shin Aoi, manager of NIED’s Earthquake and Tsunami Research Division.

Aoi estimated that the massive quake moved faults extensively across an area 150 kilometers long, and that this movement, on top of the weak ground in the area, was behind the serious damage there.