Japanese authorities are urging people across their country to take precautions against the possibility of a mega-earthquake in the coming days; if such a huge earthquake were to occur, there could be significant tsunami impacts across Hawaii and the west coast of North America.
A strong magnitude 7.1 earthquake struck southwestern Japan early on Thursday and more tremors hit the area on Friday. The Japan Meteorological Agency, the equivalent of the US-based USGS, says that seismic activity remains high and they are concerned this initial strong quake could be a precursor to a much more intense earthquake.
As a result, for the first time ever, the Japan Meteorological Agency issued an advisory for the possibility of an earthquake; the specific measure is known as the “Nankai Trough Earthquake Extra Information Protocol.”
Experts believe that the Nankai Trough quake could occur along the plate boundary between Suruga Bay in Shizuoka Prefecture and the Hyuganada Sea off Kyushu. They believe there is a 70-80% chance that it will strike within the next three decades and have a magnitude in the range of 8 to 9. However, the same experts believe there is a heightened risk that such a megaquake could occur in the coming days, which is why the Megaquake Earthquake Advisory is in effect for the next 7 days.
The Japan Meteorological Agency is urging municipalities in the region that extends from the areas around Tokyo to those in southern Okinawa Prefecture to check their earthquake preparedness. Officials are advising people to secure pieces of furniture, so that they will not fall. The authorities are also advising people to make note of evacuate sites and ways to confirm that family members are safe. They say households with infants, seniors or handicapped members should consider evacuating voluntarily.
According to a recent government estimate, in the worst-case scenario, it could claim more than 320,000 lives and destroy about 2 million buildings in Japan.
Prime Minister Fumio Kishida called on the public to “prepare to evacuate immediately if an earthquake occurs,” telling reporters in Tokyo, “To avoid unnecessary confusion, please absolutely refrain from spreading so-called false information” through social media.
In the worst-case scenario, a powerful quake could shake a wide area of Japan, from the Kanto region centering on Tokyo to the southwestern Kyushu region , and high tsunami waves could engulf the coastal areas of Kanto to Okinawa, according to the Japan Meteorological Agency.
But the tsunami threat could expand far from there. Some of the most impactful tsunamis to impact Hawaii and the North American West coast were generated by large earthquakes in Japan.
On March 11, 2011, Fukushima, Japan was home to one such megaquake. A magnitude 9.0 earthquake struck there and created a destructive Pacific-wide tsunami that destroyed buildings as far away as Hawaii. Along the coast of Japan, 30 foot waves lashed the coast, claiming the lives of more than 18,000 people. There were $220 billion in damages across Japan, with more than 400,000 homes completely or partially destroyed and more than 500,000 people displaced in the aftermath.
The earthquake generated a Pacific-wide tsunami, reaching the State of Hawai’i, and causing extensive damage to private and public property in the counties of Honolulu, Maui, and Hawaii. Over 200 waves were recorded in varying heights. The counties sustained damage of approximately $9 million. Then-President Obama declared this a Major Disaster for the State of Hawaii on April 8, 2011.
The Japanese weather agency started operating a system to release special information regarding the Nankai Trough quake in 2017, which is activated when an earthquake with magnitude 6.8 or above hits areas where megaquakes are predicted or when unusual crustal movements are observed at plate boundaries. The advisory will expire next Friday if no significant earthquake occurs. If any earthquake of consequence occurs, the Japan Meteorological Agency will issue an update.
Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases. According to the National Ocean Service, the speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves. The location, depth, movement, and intensity associated with today’s earthquake wasn’t enough to trigger a tsunami from today’s earthquake.
The United States has two tsunami warning centers, one in Hawaii and one in Alaska, that are operated by the National Oceanic and Atmospheric Administration’s (NOAA) National Weather Service. The National Tsunami Warning Center (NTWC) is located in Palmer, Alaska; this center monitors for earthquakes that could cause a tsunami and issues warnings for Alaska, British Columbia, Washington, Oregon, and California and the balance of the continental United States. The Pacific Tsunami Warning Center (PTWC), located in Honolulu, Hawaii, monitors for earthquakes that could cause a tsunami and issues warnings for Hawaii, American Samoa, Guam, Northern Mariana Islands, Puerto Rico, U.S. Virgin Islands, and the British Virgin Islands. It also serves as a national and international warning center for tsunamis that could threaten anywhere in the Pacific.
