A man examining disaster preparedness goods, taken on August 9, in Shibushi City, Kagoshima Prefecture (Photo: Kyodo News)On August 8, a magnitude 7.1 earthquake occurred off the coast of Hyuga, Miyazaki Prefecture, leading to the issuance of an interim report on the Nankai Trough earthquake, titled “Alert for Major Earthquake,” which continued to call for awareness for a week. It is said that there is a 70-80% probability of the Nankai Trough earthquake occurring within the next 30 years; but is this really true? Geologist Fumio Kakuda and former Cabinet Secretariat information analyst Kazuhiko Fujii question the mechanism that “plate movements” said to be the basis of the Nankai Trough earthquake will cause such an event. What is Kakuda’s theory of “heat transfer,” which posits that the transfer of thermal energy is the cause of earthquakes? And which areas are truly at risk? This series will run for a total of six installments. (JBpress)
(*This article is a reedited excerpt from “The Nankai Trough M9 Earthquake Will Not Occur” (by Fumio Kakuda and Kazuhiko Fujii, Hojosha).
(Kazuhiko Fujii: Former Cabinet Secretariat Information Analyst)
Three earthquakes have been consolidated into the “Nankai Trough Earthquake”
What I find most concerning is the situation where the crisis of the Nankai Trough earthquake is being overly heightened.
The increased interest in the Nankai Trough earthquake dates back about 30 years.
After the Great Hanshin-Awaji Earthquake in 1995, some seismologists living in the Kansai region began to point out that “Western Japan has entered a period of seismic activity.”
The “major earthquake” that was significant during the Great Hanshin-Awaji Earthquake referred not only to the Tokai earthquake, which had been discussed since the 1970s, but also to the Tonankai and Nankai earthquakes occurring to the west of it.
It is said that “these earthquakes have occurred in coordination in the past,” and it is this series of seismic activities that is now referred to as the “Nankai Trough earthquake.”
Subsequently, the statement that “this major earthquake is imminent” began to be heard not only from seismologists but also among disaster prevention officials.
Despite being merely a repetition of scholarly opinions, disaster prevention officials emphasized the possibility of a major earthquake happening as if it could occur at any moment.
However, when the Great East Japan Earthquake occurred on March 11, 2011, their statements changed to “unexpected.” As mentioned earlier, they had not anticipated such a super-sized earthquake at all. However, after that, it seemed like the constraints were lifted, and they began to proclaim the dangers of the Nankai Trough earthquake more vehemently than ever.
The source area of the next giant earthquake is believed to be in the Nankai Trough, off the Pacific coast of Western Japan.
The main player in the Great East Japan Earthquake was the Pacific Plate, but in the next major event, the leading role will belong to the Philippine Sea Plate located just to the west. The Nankai Trough, where the ocean plate sinks beneath Western Japan, is the final destination for the Philippine Sea Plate.
The term “trough” in Japanese translates to “boat-shaped marine basin.” It refers to a marine basin (depression) shaped like the bottom of a boat.
As the plate sinks down, it creates a gently sloping boat-shaped depression in the ocean.
In contrast, a trench is a deep, steep gully that forms where a plate sinks steeply. The Pacific Plate ends at the Japan Trench and the Izu-Ogasawara Trench.
The Nankai Trough earthquake consists of three earthquakes: the Tokai earthquake, the Tonankai earthquake, and the Nankai earthquake.
The probabilities of these occurring within the next 30 years are high: 88% for the Tokai earthquake (magnitude 8.0), 70% for the Tonankai earthquake (magnitude 8.1), and 60% for the Nankai earthquake (magnitude 8.4). Moreover, these numbers are updated annually and are gradually increasing.
These three earthquakes were originally assessed individually, but following the occurrence of the Great East Japan Earthquake, under the slogan of “eliminating unexpected events,” they were consolidated into what is now known as the Nankai Trough earthquake.