For hundreds of years, Japan, an East Asian island nation, has been deeply worried, the narrow land and lack of natural resources have greatly limited Japan's development, and more importantly, Japan, located in the Pacific Ring of Volcanic Seismic Belt, is the most frequent volcanic and earthquake-prone place in the world. What many people don't know is that there is a bigger threat lurking beneath the coast of the southern part of the island of Japan, with geophysicists warning that Japan's next magnitude 9 earthquake could erupt as a result.
In recent years, the Japan Ocean-Earth Science and Technology Agency (JAMSTEC) has used supercomputers to vigorously develop earth visualization technology, and created the first complete 3D visualization model by processing seismic data from 20 years , the Kumano Pluton, a giant igneous rock (magmatic rock) hidden several kilometers below the southern coast of Japan, known as Kumano Magma Rock.
The so-called magmatic rock is a rock formed after the magma is cooled after volcanic eruption, and often appears in the volcanic area at the junction of the crust and plate.
Thanks to the help of supercomputers, geophysicists have finally been able to get a glimpse of the rock mass hidden beneath the coast. Kumano Magmatic Rock is located in a very special location, right at the junction of the Philippine Plate and the Eurasian Plate, and is the core area of the subduction zone – which becomes an energy buffer for squeezing or colliding between the two plates. This absorption of the earth's internal energy has prevented Japan from many major earthquakes and become a lightning rod for earthquakes on the japanese island. However, things are far from being so simple...
Kumano Magma Rock Like a "Time Bomb"
As early as 1944 and 1946, the 8.2-magnitude Showa Southeast Sea Earthquake and the 8.1-magnitude Nankaido Earthquake erupted one after another, and the power of those two earthquakes could be felt as far away as Hokkaido. The source of the two earthquakes is the side of the Kumano magmatic rock (pictured below), and the researchers believe that the Kumano magma rock has accumulated a huge amount of energy during a long geological activity, which is like a "time bomb" that can detonate at any time.
The analysis shows that the Kumano magmatic rock extends down the subduction layer under the southern coast of Japan, and its scale is like a majestic mountain range. 3D seismic imaging near the subduction zone showed that Kumano magmatic rocks had a greater density than the surrounding rocks, and as a result, the crustal layer below had been bent by Kumano magmatic rocks. To make matters worse, the mass opened up a waterway from the earth's crust to the deep mantle, allowing seawater to seep into the mantle layer continuously. It is conceivable that the Kumano magmatic rocks are profoundly changing the geological structure of southern Japan, and it is likely to trigger a larger earthquake (magnitude 8-9).
Predictions for a magnitude 9 mega earthquake in Japan
As early as 10 years ago, on the evening of March 31, 2012, a news that Japan could erupt into a magnitude 9 earthquake was frantically forwarded. The Earthquake Expert Committee of the Cabinet Office of Japan met and issued a forecast report that a "super earthquake" of magnitude 9 on the Richter scale will occur in the area centered on the coast of Osaka and Kobe, and the height of the tsunami will reach 34 meters, equivalent to 10 stories high, and the tsunami may affect the coastal areas of Jiangsu and Zhejiang on the mainland and directly hit cities such as Shanghai. Soon, the Zhejiang Provincial Earthquake Bureau responded in writing, saying:
"Experts believe that even if a magnitude 9 earthquake occurs in the South China Sea, it is unlikely to have a destructive impact on the coast of Jiangsu and Zhejiang." The rationale for this result is that even if a strong earthquake occurs in Japan, the resulting tsunami will decay significantly before it reaches China.
As for Japan, the island with the most seismic volcanoes in the world, I'm afraid it's not that lucky. In recent years, there have been reports of strong earthquakes in Japan, which shows that they are not out of thin air. For example, Japanese officials have estimated that Tokyo, a super-city of nearly 40 million people, will be hit by a mega-earthquake every 100 years, which could kill tens of thousands of people, and seismologists believe that the window of the Tokyo earthquake has arrived, and that the Tokyo area may be hit by a strong earthquake at any time in the next 30 years.
The Kumano magmatic mass was first discovered in 2006, but it is only today that its full picture has come into view. Adrien Arnulf of the University of Texas' Institute of Geophysics said the discovery could provide "eye-opening" insights for other regions.
Shuichi Kodaira, a geophysicist who conducted the collaborative study, also said that although it is impossible to accurately predict the future, it will at least provide very important data for the Japanese people, hoping that Japan will prepare for the next devastating earthquake.
In any case, hopefully Japan is fully prepared ...
参考文献：Adrien F. Arnulf et al, Upper-plate controls on subduction zone geometry, hydration and earthquake behaviour, Nature Geoscience (2022).