A weeklong government call for increased preparedness based on an advisory over a potential megaquake along the Pacific coast officially ended 5 p.m. Thursday, after no new major seismic activity was confirmed around the Nankai Trough.
The Nankai Trough megaquake advisory, the first since the system was implemented in 2017, prompted the central government and local communities to intensify disaster preparations over the past week. It also negatively impacted some tourism-related businesses during the summer holiday season.
Japan, a quake-prone nation, has long feared a magnitude 8 to 9 quake along the Nankai Trough within the next 30 years, with predictions that a wide area could be jolted and vast coastal regions engulfed by massive tsunami.
The megaquake advisory was issued just hours after a M7.1 quake rocked southwestern Japan on Aug. 8, with its focus located in waters off Miyazaki Prefecture, on the western edge of the Nankai Trough.
The advisory is intended to inform the public of the higher-than-usual risk of a large-scale quake around the Nankai Trough for a week.
"We urge the public to remain prepared, as the possibility of a major temblor has not been eliminated," disaster management minister Yoshifumi Matsumura said at a press conference Thursday.
Aitaro Kato, a professor of seismology at the University of Tokyo, stressed that a megaquake in the Nankai Trough is not the only risk to Japan, reminding those outside potentially affected areas "to also remain vigilant while efforts to stockpile supplies and reinforce buildings against earthquakes should continue nationwide."
The Nankai Trough is an ocean-floor trench that runs along Japan's Pacific coast where the Eurasian and Philippine Sea tectonic plates meet.
The Japan Meteorological Agency stated that as of Wednesday, it had detected no seismic activity indicating any concerning changes in the presumed area where the megaquake could originate.
According to the Cabinet Office, the advisory has been applied to 707 municipalities across 29 prefectures where strong shaking and large tsunami are expected in the event of a major quake.
The two government bodies at a joint press conference Thursday acknowledged that the first-ever advisory had raised alarm among the public, with one of the officials saying, "We would like to consider improvements to operational procedures as needed based on the social response."
They noted that 24 earthquakes registering at least 1 on Japan's 7-point seismic intensity scale had been observed in and around the presumed area where the megaquake could occur in the week through 5 p.m. Thursday.
The government estimates that, in a worst-case scenario, a megaquake in the Nankai Trough could result in over 200 trillion yen ($1.36 trillion) in damage.
A M9.0 earthquake with an epicenter near land would increase the damage due to the collapse of housing and infrastructure, as well as reduced business activity.
Kuroshio in Kochi Prefecture, western Japan, where a 34-meter tsunami is expected in the event of a megaquake, responded to the advisory by establishing a disaster response headquarters and increasing the number of disaster response staff.
According to the prefecture, over 100 evacuation centers have been established, with up to 63 people having sought refuge.
Many railway and travel companies on Thursday ended cancellation fee waivers implemented in the wake of last week's quake. The move was in line with the one-week period of the advisory's call for increased preparedness, although some companies have extended the waivers due to an approaching typhoon.
Some beaches in western and southwestern Japan that were closed for swimming following last week's quake have also reopened.
History shows that a major earthquake around the Nankai Trough occurs every 100 to 150 years. About 80 years have passed since the most recent.
The quake that devastated northeastern Japan on March 11, 2011, triggered massive tsunami and led to the Fukushima Daiichi nuclear power plant disaster. It registered a M9.0, the strongest earthquake ever recorded in Japan.
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