|Early on April 14th and 16th, a series of massive earthquakes hit Kumamoto and Oita prefectures. They took many precious lives and assets. I would like to express my deepest condolences to the victims.
Earthquake Fault Lines
When I heard the news of the first earthquake around 9.00 pm on April 14th, I couldn’t believe it. I had never imagined that such a large earthquake would hit these areas, though I knew they were susceptible to eruptions of Mt. Aso in Kumamoto.
More surprisingly, the magnitude 6.5 main quake was followed by a magnitude 7.3 quake in the early hours of April 16th. Later, there was an announcement that the earthquake on the 16th was the main quake and the previous one on the 14th was a fore-shock.
It is believed that the earthquake on the 14th occurred on an active fault called the Hinagu Fault Belt. Since then, aftershocks have continued and the epicenter's area has stretched northeast into Oita prefecture. Experts are analyzing the causes of these earthquakes, and details will be gradually revealed.
I have dealt with topography and geological conditions across Japan as a river improvement engineer for twenty years. Looking at the distribution of earthquakes, it seems as though the median tectonic line has moved. This median tectonic line was formed during the Cretaceous Period, about 65 to 145 million years ago. It had been thought that such old fault lines would never move. Therefore, no one imagined that the median tectonic line would move. However, when I look at the distribution of epicenters and the stretching of the epicenter to the northeast, it seems to coincide with the median tectonic line.
Those responsible for disaster risk management across the world call Japan “a show window of disasters”. It is true that the country fall victim to all sorts of disasters. In fact, there is no type of disaster that Japan doesn’t experience. There are earthquakes, tsunamis, volcanic eruptions, typhoons, heavy rains, floods, storm surges, heavy snow, avalanches, lightning, tornadoes, landslides, cold-weather damage, and droughts. Among these, the earthquake is the harshest, because it strikes unexpectedly, without warning.
Near the Japanese archipelago, four major tectonic plates collide with each other. Because of this, 20 percent of the earth’s major earthquakes and 10 percent of its active volcanoes occur in Japan, though the country accounts for only 0.3 % of the earth’s surface. The figure below illustrates this.
About 3,000 years ago, the Japanese people began to grow rice on their islands. At that time, the alluvial plains were wetlands surrounded by mountains on one side and the sea on the other. This land formation bordered by mountains, oceans and rivers prevented the Japanese people from moving to other areas. Therefore, they formed rice-growing communities and worked together to recover from the damage caused by whatever disasters they faced.
It is difficult to come to terms with an earthquake, which strikes us unexpectedly without warning. It is an unexplained phenomenon. The cause of an earthquake is always explained after the fact. If we can call something unexplained “irrational”, nothing is more irrational than an earthquake.
I can only pray that all those affected by this latest disaster will overcome their hardships and build stronger communities.