TOKYO -- Japan on Thursday said the possibility of a huge earthquake over a wide swath of central and western parts of the country has increased relative to normal conditions following a magnitude 7.1 temblor off Miyazaki prefecture on the southern island of Kyushu earlier in the day.
Following the afternoon quake, the Japan Meteorological Agency launched investigations into its possible relationship to a potential Nankai Trough earthquake, which experts have warned for years could cause huge loss of life and property across a wide stretch of central and western Japan. The trough is a marine trench running along part of the south of the Japanese archipelago.
The agency issued its Nankai Trough Earthquake Extra Information for the first time ever on Thursday evening. An accompanying government advisory said the "possibility of a large-scale earthquake is considered to be relatively higher than under normal conditions." According to the agency, the large earthquakes have taken place every 100 to 150 years in central and western areas of the country.
The government has previously said there is a 70% chance of such an earthquake within 30 years. And while Naoshi Hirata, an earthquake expert and emeritus professor at the University of Tokyo, said at an agency news conference that "the probability is multiple times higher than usual" after the Miyazaki earthquake, it remains "an event of one in a multiple hundred times." Still, he urged people to be prepared.
Prime Minister Fumio Kishida also called on the public to check their earthquake preparations and "be ready to evacuate immediately if an earthquake occurs."
There have been no reports so far of major damage from Thursday's 7.1-magnitude quake and the small tsunamis it generated. Chief Cabinet Secretary Yoshimasa Hayashi said the government "has not received any reports of abnormalities" at nuclear plants and related facilities in the region.
The agency urged caution for a week, with the probability of large earthquakes being higher just after the Miyazaki quake. But its representatives repeatedly emphasized that such large earthquakes could happen anytime, even beyond a certain period.
Japan is one of the world's most earthquake-prone nations because of its location on the Pacific "Ring of Fire," an arc of volcanoes and fault lines encircling the Pacific Basin. Japan was struck by a triple disaster in March 2011, when a magnitude-9 earthquake off the northeast coast triggered a deadly tsunami, leading to three meltdowns at the Fukushima Daiichi nuclear plant.
The agency said a Nankai Trough earthquake may be limited to the vicinity of Thursday's quake or extend over the "entire Nankai Trough."
Experts say a Nankai Trough earthquake could span areas ranging from the islands of Kyushu, Shikoku and parts of Honshu including Aichi and other prefectures to areas farther east closer to Tokyo such as Shizuoka prefecture -- simultaneously or in succession at a magnitude of up to 9.
Such a quake could also lead to a tsunami of over 30 meters and together cause up to 320,000 deaths and economic losses of 220 trillion yen ($1.5 trillion), according to a government estimate in 2012.
It has been over 70 years since the last major earthquake disaster in the region, which experts say makes such an event ever more likely.
Kishida is scheduled to travel to the city of Nagasaki on the island of Kyushu to participate in annual commemorations of the 1945 U.S. atomic bombing of the city on Friday, and also depart for Kazakhstan later in the day for a summit with Central Asian nations. He is also slated to visit Uzbekistan and Mongolia. It was not immediately clear if the heightened Nankai Trough earthquake risk would impact his plans.
He said the government will "make appropriate decisions" based on information it is collecting.
