Concern about a megaquake striking Japan has grown after the weather agency issued its first advisory of the increased risk of a temblor occurring around the Nankai Trough along Japan's Pacific Coast, following a magnitude 7.1 quake in the country's southwest last week.
The following are questions and answers about the Nankai Trough earthquake, where it could strike and what appropriate measures should be taken to prepare.
Q: What is a Nankai Trough earthquake?
A: A Nankai Trough earthquake is a potentially devastating temblor occurring in the Nankai Trough, an oceanic trench that runs along the Pacific coast of Japan, where the Eurasian and Philippine Sea tectonic plates intersect.
A Nankai Trough quake has occurred every 100 to 150 years. The last confirmed quakes linked to it were the 1944 Tonankai and 1946 Nankai earthquakes, which together struck a wide area from central to southwestern Japan.
A magnitude 8 to 9 earthquake has a 70 to 80 percent chance of occurring within 30 years, according to a government estimate.
According to a government pamphlet, the earthquake could in some areas register the highest level of 7 on Japan's seismic intensity scale, making it impossible for a person to remain standing and causing buildings to crack or collapse. Tsunami waves of over 30 meters are also projected in a worst-case scenario.
Q: How deadly could a potential earthquake be?
A: Estimates from 2012 for a worst-case scenario show up to 323,000 people could die due to a powerful Nankai Trough quake and its effects.
Japan is a quake-prone nation. More than 18,000 people died or went missing after a magnitude 9.0 earthquake and subsequent tsunami devastated northeastern Japan on March 11, 2011, according to National Police Agency data.
Q: Which areas are at high risk?
A: Areas projected to be at high risk include the prefectures of Shizuoka, Wakayama, Kochi, Aichi, Ehime and Oita stretching from central to southwestern Japan.
Depending on its location, the earthquake could trigger tsunami waves in areas ranging from Ibaraki Prefecture in eastern Japan, along the Pacific coast and all the way to the southern island prefecture Okinawa.
The town of Kuroshio and the city of Tosashimizu in Kochi Prefecture could be hit by the highest tsunami waves at 34 meters, while a 33-meter high tsunami could hit Shimoda in Shizuoka Prefecture.
Q: How likely is a devastating earthquake in the near future?
A: Data from the weather agency shows that the probability of a powerful earthquake increases in the seven days after a temblor of magnitude 7.0 or more.
Among quakes linked to the Nankai Trough, the 1854 Ansei Tokai earthquake was followed around 32 hours later by the Ansei Nankai earthquake.
Q: What measures should be taken to prepare for a disaster?
A: In the case of major disasters, households are encouraged by the government to have a week's food and drinking water for each member, based on a daily usage of 3 liters per person.
The website of the prime minister's office also recommends preparing a bag in case evacuation is required, containing essentials such as food, water, rainwear, flashlights and clothing, as well as documents such as passports and bank books.
Residents are advised to confirm the route to their local evacuation centers by using hazard maps, available on local government websites, and the Ministry of Land, Infrastructure, Transport and Tourism's Disaster Prevention Portal site.
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