The Kumamoto Earthquakes

During the night of April 14, a major earthquake, registering magnitude 7 on the Japanese seismic scale, struck the area of Mashiki-machi town in Kumamoto City. I must say that I was astonished by the stated seismic figure of 7. This relates to the fact that upon the Great East Japan Earthquake of 2011, we experienced seismic intensity of upper 5 in Tokyo, shaking that resulted in groups of huge buildings swaying back and forth. While an intensity level of 7 defies the imagination, a series of temblors measured at the upper 6 level followed that initial shaking.

It was reported that Mashiki-machi is where the Futagawa and Hinagu fault zones intersect. We also learned that the intensity 7 earthquake struck due to the shifting in location of the north side of the Hinagu fault zone over the passage of time.

Following this, the wee morning hours of April 16 brought the main shock, tracked at magnitude 7.3. The Geographical Survey Institute announced that this quake occurred in the Futagawa fault zone. It likewise became clear that the energy released in this main shock was 1.4-times larger than that of the Great Hanshin-Awaji Earthquake of 1995. In the wake of this principle earthquake, furthermore, more shocks have been occurring in the three regions of Kumamoto, Aso and Oita.

Although I was born in Bungo Ono City in Oita Prefecture, this was the first time I had ever heard mention of the Beppu-Haneyama fault zone. Under the impact of the main shock, on April 18 earthquakes of intensity 6 occurred in the cities of Beppu and Yufu, with an upper 5 quake also hitting Takeda City. According to the Meteorological Agency: “There is no precedent for earthquakes to occur in the three distant locations of the Kumamoto region, the Aso region and the central area of Oita Prefecture.”

The “Beppu-Shimabara Graben” stretches from Oita Prefecture to Kumamoto Prefecture, cutting through the Kyushu region in an east-west direction. It is conceivable that such a chain of events is initiated when movement occurs at one fault followed by an earthquake, with the strains that accumulate in the vicinity of that fault triggering further tremors. Considering this, it would appear that this area has truly entered a seismically active phase.

From the time I was a young boy, I felt captivated by two different waterfalls – Harajiri Falls and Chinda Falls. While Chinda Falls contains the remains of a power station, it is also considered a great waterfall visited in the past by historian Sanyo Rai and other persons of note. Then again, it is Harajiri Falls that is included in the list of Japan’s 100 most beautiful waterfalls, and is particularly spectacular for retaining its original natural state.

Stretching 120 meters across and 20 meters in height, Harajiri Falls is truly worthy of its nickname – the “Niagara of the Orient.” It was formed from a lava plateau generated by the massive pyroclastic flow that followed a huge eruption of Mt. Aso some 90,000 years ago. That plateau was eroded by the steady flow of water over the millenniums, effectively pushing down the pillar of the columnar jointing formed after the lava flow cooled.

Be that as it may, the recent rash of earthquakes may also be said to provide a wakeup call for the underlying ties with the ancient eruption of Mt. Aso, the subsequent pyroclastic flow and other geological developments. I say this because the foundation of this region cannot be said to be solid in any true sense of the word. Thus, I can only pray that this seismic activity comes to an end sooner than later, while extending my heartfelt sympathy to those impacted by this disaster.