Photo/Illutration A May 5 earthquake caused boulders to topple down a hillside in Suzu, Ishikawa Prefecture. (Hiroyuki Kojima)

A buildup of water deep underground may be behind more than 300 swarm earthquakes that have made life a misery for residents of Suzu city, Ishikawa Prefecture, over the past two years or so, researchers say.

An earthquake on the afternoon of May 5 that registered upper 6 on the Japanese intensity scale of 7 was described as much worse in terms of property damage than one of lower 6 that struck in June of last year.

Tetsunori Takayama, a 57-year-old priest at Hagurojinja shrine in Suzu, was at home with his wife and mother when the quake hit.

He expressed relief that his family was unharmed but was shocked by the damage to the shrine’s stone torii gate and the roof of a “chozuya” purification fountain.

The shrine was also damaged in the last year’s quake.

Shuichi Iwagaki, a 53-year-old monk who lives in the city, said: “The temblor was worse than the one last year. Residents standing outside were petrified.”

The scenic Noto Peninsula has experienced scores of earthquake swarms in recent years.

The Japan Meteorological Agency said 313 quakes measuring at least 1 on the Japanese seismic intensity scale of 7--the smallest class that can be felt by humans--struck the area between December 2020 and shortly before the May 5 quake.

Eleven of them measured at least 4 on the Japanese scale.

The quake that hit on June 19, 2022, had an intensity of lower 6. Stone torii gates at two shrines in Suzu collapsed in the quake. A quake the following day had an intensity of upper 5.

The latest quake was the biggest to date, JMA officials said.

Some scientists believe that water accumulating beneath seismic source areas is responsible for the quakes.

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Takuya Nishimura, a professor of geodesy at Kyoto University’s Disaster Prevention Research Institute, said, “The same mechanism that caused swarm earthquakes in the Noto Peninsula appears to have caused the latest earthquake, too, and ‘water’ has something to do with it.”

Junichi Nakajima, a professor of seismology at Tokyo Institute of Technology, also agreed that water could be behind the quakes.

But Nakajima, noting that swarm earthquakes rarely produce temblors with a magnitude of 6 or more, said it remains unclear why this quake was bigger.

He cautioned that similar quakes were possible in the future.

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