National

Hokkaido and Pacific coast now understood to face higher risk of powerful earthquakes

Kyodo

The government released its annual update to Japan’s earthquake probability map on Tuesday, indicating an increased likelihood of strong earthquakes occurring within the next 30 years across a wide area of the Pacific coast including parts of Hokkaido.

The map showed a sharp increase in the probability of a powerful earthquake, measuring lower 6 or stronger on the Japanese seismic intensity scale of 7, in Kushiro, Hokkaido, in the next 30 years, jumping 22 percentage points to 69 percent.

The sharp rise reflected research suggesting major earthquakes accompanying massive tsunami have repeatedly occurred along Chishima Trench, off eastern Hokkaido, in the past.

Elsewhere in Hokkaido, the likelihood of such a quake rose 15 percentage points in both Nemuro and Hidaka to 78 percent and 70 percent, respectively.

The most recent major earthquake hitting Japan’s Pacific coast area occurred in March 2011. The magnitude 9.0 quake triggered a huge tsunami that inundated northeastern coastal regions, leaving over 18,000 people dead or presumed dead.

More recently, earthquakes registering a low or high 6 have occurred in the southwestern region centering on Kumamoto in April 2016, the western prefecture of Tottori in October 2016 and Osaka in June this year.

As of Jan. 1, the probability of such a quake remained high for the greater Tokyo region, Shizuoka in central Japan, parts of the western region of Shikoku and the Kinki region — which includes Osaka.

In a quake with an intensity of lower 6, it is difficult for people to remain standing, and furniture moves or topples over. Older wooden buildings with low seismic resistance could collapse.

“We want people to be mindful of the fact that an earthquake can strike anywhere,” said science minister Yoshimasa Hayashi, who oversees an earthquake survey panel. He urged people to take necessary measures to minimize damage.

Located in the Kanto region around Tokyo, where many crustal plates overlap, Chiba had the highest probability among Japanese cities of a major quake, at 85 percent. That was followed by 82 percent for Yokohama, which is near the Sagamihara Trough, and 81 percent for Mito — both a 1 percentage point increase from the year before.

Shizuoka’s quake risk stood at 70 percent, up 1 percentage point from the year before as the city could be hit by a major earthquake along the Nankai Trough that extends southwest from the Pacific Coast. The updated evaluation of risk related to the Nankai Trough left the probability for Nagoya at 46 percent and Wakayama at 58 percent, according to the report.

The probability of a major earthquake occurring in the Nankai Trough has generally been rising every year as it is assumed to occur in a cycle and a major earthquake last occurred there in 1946.

All four prefectures on the island of Shikoku saw the probability rise by 1 to 2 percentage points from the previous year, as experts re-evaluated risks posed by the massive active fault zone along the median tectonic line that stretches over the Kinki, Shikoku and Kyushu regions. The city of Kochi marked 75 percent probability.

A number of cities in Kinki also have substantial risks of a strong quake, at over 50 percent, as the western Japan region has a number of active faults and has large plains prone to tremors, the panel said.

Naoshi Hirata, who heads the government panel that compiled the latest report, urged people to check that their homes, offices and local buildings have sufficient quake resistance and to reinforce the structures if necessary.

“There is no place with zero probability of experiencing an earthquake with an intensity of lower 6 or more,” he said.

The latest estimates are available on the website of the National Research Institute of Earth Science and Disaster Resilience, allowing visitors to check on probabilities by address.

As Japan is prone to earthquakes, the government has been releasing the map almost annually since 2005 to help residents, firms and municipalities prepare for major earthquakes.