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A series of earthquakes in central and western Japan on Friday fueled fresh fears of a “Big One” and disastrous volcanic eruptions in the world’s most seismically active nation.

The first significant convulsion was a magnitude 4.8 temblor that struck the northern foot of Mount Fuji at around 6:37 a.m. The quake registered a weak 5 on the 7-point shindo seismic intensity scale in Otsuki in eastern Yamanashi Prefecture and 4 in some areas of Kanagawa Prefecture, the Meteorological Agency said.

While there was no threat of a tsunami following the quake, which was also felt in parts of Tokyo, the agency warned that shakes of similar intensity could occur within a week. The epicenter of the quake in the Fuji Five Lakes area was at a depth of about 19 kilometers, it said. There were no initial reports of injuries or serious damage to infrastructure, according to the authorities.

Quakes are part of everyday life in Japan. The archipelago sits on or near the boundaries of four tectonic plates and lies along the seismic Pacific Ring of Fire, where a majority of the planet’s earthquakes and volcanic eruptions occur. In fact, 18.5% of earthquakes in the world take place in Japan, according to the land ministry. That effectively means quakes can happen anywhere in the nation at any given time.

Still, the Friday morning shaker raised alarm because it was preceded by earlier quakes of magnitude 4.1 and 3.6 that hit at around 2:18 a.m. and 2:23 a.m., respectively, in the same area.

“Mount Fuji eruption” immediately began trending on Twitter, with netizens voicing anticipation that the quakes could trigger a major volcanic eruption at Japan’s highest peak. The Meteorological Agency tried to quell the unease, saying there was no particular change in observational data for the 3,776-meter mountain.

As if to fan the flames, however, a magnitude 5.4 earthquake then struck off western Wakayama Prefecture at 9:28 a.m., registering a weak 5 on the seismic intensity scale in the prefecture’s city of Gobo. While no injuries have been reported so far from the quake, which registered as high as a shindo 3 in Osaka, the area is among those considered at risk of a megathrust earthquake centered on the Nankai Trough, a massive ocean-floor trench stretching off the southern coast of Japan from Shizuoka Prefecture to the island of Kyushu.

Windows are broken at the Gobo city office in Wakayama Prefecture, following an earthquake on Friday morning. | KYODO
Windows are broken at the Gobo city office in Wakayama Prefecture, following an earthquake on Friday morning. | KYODO

The government estimates that a violent quake of magnitude 8 to 9 has a 70-80% probability of striking along the trough within the next 30 years, with the disaster projected to kill as many as 320,000 people and cause damage of up to ¥220 trillion.

“As with the earthquake in Yamanashi, the quake in Wakayama is also affected by the Philippine Sea Plate,” said Manabu Takahashi, a specially appointed professor at Ritsumeikan University’s Research Center for Pan-Pacific Civilizations.

“It feels like the entire Japanese archipelago is at the mercy of the power of the plates. In particular, volcanic activity and earthquakes are likely to occur at Mount Fuji, Mount Hakone, Izu Oshima island, Miyake Island and other areas on the west side of the Izu-Ogasawara Trench where the Pacific Plate sinks into the Philippine Sea Plate,” he said.

“We should be bracing for the possibility of unprecedented earthquakes and volcanic eruptions.”

Researchers have been warning that seismic activity has been increasing since March 11, 2011, when a magnitude 9 earthquake struck off the northeastern coast of Japan, triggering massive tsunamis, killing nearly 16,000 people and leaving thousands more missing. That quake — the largest in the nation’s recorded history — was accompanied by widespread crustal displacements that have been creating stress and triggering earthquakes, they say.

The greater Tokyo area, which includes Yamanashi Prefecture, where the tremors occurred Friday, is located on three layers of plates: the Okhotsk Plate from the north, the Philippine Sea Plate from the south sliding under it and the Pacific Plate from the east underlying them both. These plates constantly grind together, triggering deadly quakes.

In October, a magnitude 5.9 earthquake struck Tokyo and its surrounding prefectures. All train and subway lines in and around the capital temporarily halted operations while water pipes burst and fires broke out. While no one was killed, the convulsion reignited fears of a giant quake that could see the capital left in ruins

In 2013, the government issued a report predicting that there is a 70% chance of a magnitude 7 earthquake striking the capital region in the next 30 years. In a worst-case scenario, the quake could kill up to 23,000 people, cause more than ¥95 trillion in damage and destroy 610,000 homes.

“Eastern Yamanashi, where the quakes have taken place this morning, sits on plate boundaries and has been a very seismically active area,” says Toshiyasu Nagao, an expert on earthquake prediction at Tokai University’s Institute of Oceanic Research and Development.

“But the region has been relatively quiet for the last decade or so. These recent quakes indicate that the area is becoming seismically active again.”

Meanwhile, Nagao says Mount Fuji is due for its next blast, since the last eruption was in 1707. If the iconic mountain erupts, volcanic ash could travel past Tokyo all the way to Chiba and paralyze the capital and surrounding areas, causing blackouts, water shortages and disrupting telecommunications, according to a government task force.

“While there may be no detectable signs of an eruption at this point, it will definitely happen, likely during our lifetime,” he says.

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