Over 20m-tsunami could hit Sea of Japan

August 27, 2014

Tsunami risk in Sea of Japan region just as high as Pacific coastline

http://ajw.asahi.com/article/behind_news/social_affairs/AJ201408270056

THE ASAHI SHIMBUN

A panel of experts has found that the previously unexamined Sea of Japan region is just as vulnerable to devastating tsunami in a big earthquake as the Pacific Ocean coastline on the opposite side of the country.

The study was undertaken in light of the March 11, 2011, Great East Japan Earthquake that generated tsunami in Pacific waters, turned parts of the Tohoku region into a wasteland and triggered a triple meltdown at the Fukushima No. 1 nuclear power plant.

The experts said tsunami as high as 23.4 meters could strike Setana in western Hokkaido. Estimates were calculated for 173 municipalities in 16 prefectures facing the Sea of Japan.

Tsunami heights were also estimated for areas that host nuclear power plants.

The maximum height of one projected to hit the Tomari plant in Hokkaido was 5.8 meters.

A 3.8-meter-high tsunami was expected to reach the Shika nuclear plant in Ishikawa Prefecture, while one of 3.4 meters was projected for the Kashiwazaki-Kariwa plant in Niigata Prefecture.

The estimates were all below the expected tsunami heights previously announced by electric power plants for the 11 nuclear plants, including those under construction and covered by the latest study.

A panel member said: "Faults are shallower on the Sea of Japan side in comparison to the Pacific side, and the angle of movement is sharper so tsunami heights become larger in comparison to the scale of the quake. Tsunami also reach land more quickly because the faults are closer to land."

In some areas, it was calculated that tsunami would arrive just one minute after the earthquake struck.

The panel of experts, which was brought together by the land ministry, the Cabinet Office and science ministry, selected 60 major faults in the Sea of Japan and estimated the effects of earthquakes ranging in magnitude from 6.8 to 7.9.

The members simulated 253 tsunami patterns on the basis of location, angle and length of the fault. Estimates were then made of the maximum tsunami height for 50-meter squares drawn up along the coastal area extending from the Shiretoko Peninsula of Hokkaido to Hirado, Nagasaki Prefecture.

According to the estimates, the other area where a tsunami exceeding 20 meters would likely hit was Kamoenai, Hokkaido. The maximum height was put at 20.3 meters.

A total of 30 municipalities in six prefectures were expected to be hit by tsunami exceeding 10 meters.

The panel also released estimates for areas that could be considered ordinary residential districts located within 200 meters or so from the coast and with an elevation of under 8 meters.

The highest estimate was for Okushiri, Hokkaido, where the maximum tsunami height was calculated to be 12.4 meters.

The region from Hokkaido to Fukui was expected to be hit by tsunami ranging in height between 5 to 12 meters, while the region from Kyoto to northern Kyushu was likely to see tsunami between 3 to 4 meters high.

Calculations were also made on how quickly tsunami of at least 30 centimeters would strike after the quake.

The tsunami would reach 15 municipalities in six prefectures within a minute after the quake. Among those municipalities are Okushiri and Sakata, Yamagata Prefecture. The tsunami was expected to reach 82 municipalities in 14 prefectures within 10 minutes.

Tsunami was expected to reach the city of Niigata in seven minutes and Fukuoka in eight minutes.

No calculation was made on how quickly the maximum estimated tsunami would reach a particular location because panel members said the speed would differ depending on the quake.

August 27, 2014

Over 20-meter tsunami could hit Sea of Japan coast: gov't panel

http://mainichi.jp/english/english/newsselect/news/20140827p2g00m0dm036000c.html

TOKYO (Kyodo) -- A tsunami of over 20 meters could hit a town on the Sea of Japan coast, a government panel on large-scale earthquakes said Tuesday.

The town of Setana in Hokkaido faces the biggest potential tsunami hitting coastal areas on the Sea of Japan at 23.4 meters high, according to the panel, which studied heights of possible tsunamis covering 16 prefectures from Hokkaido in the north to Nagasaki in the southwest.

The largest possible tsunami to hit flat land areas would be 12.4 meters high in the town of Okushiri in Hokkaido, according to the study.

The first study on tsunami on the Sea of Japan coast will be used by prefectural governments for estimating inundation and designating warning zones.

The government is expected to ask municipal governments to bolster their safety measures as faults in the Sea of Japan tend to be close to land areas, possibly causing relatively high tsunamis to hit the coast quickly.

As for 11 nuclear power stations on the coast, a 5.8-meter tsunami could reach an area near Hokkaido Electric Power Co.'s Tomari nuclear power plant while a 3.8-meter tsunami could hit an area near Hokuriku Electric Power Co.'s Shiga nuclear plant in central Japan, the panel said.

The study showed relatively higher tsunamis could be observed in northern parts of the coastline compared with other parts and some areas could be hit by a first tsunami wave about a minute after an earthquake.

The study selected 60 faults on the seabed where an earthquake with a magnitude of 7 to 8 could be triggered. It was compiled after legislation was established to strengthen measures against tsunamis following the 2011 earthquake and tsunamis that devastated northeastern Japan.

August 27, 2014(Mainichi Japan)