Calming Fears: Experts doubt quake will impact volcanoes in Japan’s Kyushu region

April 2016 – JAPAN – The Kyushu region is home to many active volcanoes, but experts believe Thursday’s powerful earthquake in Kumamoto Prefecture is unlikely to trigger significant volcanic activity in the region. Active volcanoes in the region include Mt. Aso in Kumamoto Prefecture, Sakurajima in Kagoshima Prefecture and Mt. Unzen in Nagasaki Prefecture. After the Great East Japan Earthquake in 2011, heightened activity was detected at volcanoes including Mt. Hakone, which sits on the border of Kanagawa and Shizuoka prefectures. However, experts doubt Thursday’s earthquake will trigger such a phenomenon, as it was not a large-scale earthquake that had an impact over a wide area, and therefore is unlikely to have any connection to these volcanoes.

The closest volcano to the quake’s origin is Mt. Aso, which is about 35 kilometers away. The volcanic alert level for Mt. Aso is 2, meaning people should not approach the crater. “An active fault moved at quite a shallow depth,” said Toshitsugu Fujii, chairman of the Japan Meteorological Agency’s Coordinating Committee for Prediction of Volcanic Eruptions and a professor emeritus at University of Tokyo. “Magma didn’t set off this earthquake. Therefore, there is very little possibility of it having any effect on the magma under Mt. Aso.” This view was echoed by Kazuhiro Ishihara, deputy chair of the committee.

“Mt. Aso has always been active, so even if there’s a temporary increase in slight tremors, a major eruption won’t happen anytime soon,” said Ishihara, a professor emeritus at Kyoto University. “There’s no need to worry, provided people remain outside the restricted area.” Ryusuke Imura, an associate professor at Kagoshima University and an expert in volcanic geology, also doubted there would be any connection between the earthquake and volcanic activity. “But the volcano needs to be continually monitored, just in case,” Imura said. –The Nation

Seismic activity could move east, and trigger more quakes in active faults

Seismologists fear that the series of earthquakes rattling Kyushu could trigger temblors in other active faults in the southwestern island, which extend eastward into central Japan. A number of active faults dot the so-called Beppu-Shimabara Rift, which traverses Kyushu Island from east to west, extending to the Median Tectonic Line. This is the nation’s longest tectonic line, and it spans about 1,000 kilometers from the Kanto Plain through Gunma, Nagano, Wakayama, and Tokushima prefectures to Kyushu Island in southern Japan. Ichiro Kawasaki, professor emeritus of seismology at Kyoto University, said: “The epicenter (in the latest series of quakes that began April 14) is gradually moving eastward. When a fault moves, it tends to move other faults that run on an extended line.”

He explained that when an earthquake occurs, other faults around it are exerted to different pressure, which could trigger other quakes. That view was echoed by Kazuro Hirahara, a Kyoto University professor of seismology and head of the Coordinating Committee for Earthquake Prediction. “The epicenter of the earthquake in Oita Prefecture, (which occurred early on April 16) is about 100 kilometers from that of the Kumamoto quakes, and therefore it is hard to think that the quake was an aftershock,” he said, adding that there was a possibility the Beppu-Haneyama fault zone in the prefecture may have been stimulated.

“Quite frankly, there is no telling what may happen in the days ahead,” he said. “If some part in the Median Tectonic Line moves, there is a chance it could have an impact on the predicted Nankai Trough Earthquake in the long run.” Shinji Toda, a Tohoku University professor of earthquake geology, pointed out that the seismic activity could also move southward. –ASAHI