Playback ’16] Bridges Collapsed and Kumamoto Castle Collapsed… Kumamoto Earthquake Struck Twice with Seismic Intensity 7 in Just 28 Hours

A loud “gurgling” sound was accompanied by a huge tremor.

What did “FRIDAY” report 10, 20, or 30 years ago? In “Playback Friday,” we revisit the topics that were hot at the time. This time, we take a look at the May 6, 2004 issue, which was published 10 years ago, in the section “Is the M7.3 Kumamoto Earthquake the Beginning of the Next Terror?

At 9:26 p.m. on April 14, 2004, a major earthquake of magnitude 6.5 occurred in the Kumamoto region of Kumamoto Prefecture, and a seismic intensity of 7 was recorded in Mashiki Town in the same prefecture. By the evening of the following day, April 15, nine people were dead, 12,300 houses were without power, and 80,500 houses were without water. Just 28 hours later, however, the “main quake” struck Kumamoto, causing even greater damage… (Descriptions in parentheses are quotations from past articles, titles are those of the time).

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The reporter who experienced the “main quake” on site described the situation at the time of the quake in his article as follows.

At 1:25 a.m. on April 16, this reporter, who was sleeping in a hotel in Kumamoto City, was awakened by a strong shock that felt like a jolt. The next moment, he was hit by a huge tremor with a “thumping” sound. The canned coffee on the table and the 30-inch TV on the shelf fell one after another.

After the shaking subsided, I took the emergency stairs down to the lobby, where I found water spewing from the ceiling. The building’s water tank seemed to have burst, and the sound of a waterfall was echoing from the cafeteria next to the lobby.

Overnight in Kumamoto City, signboards had fallen down everywhere in the shopping district, and debris was scattered here and there. At Kumamoto Castle, two turrets designated as important cultural properties collapsed along with their stone walls.

The reporter for this magazine traveled to Mashiki Town in Kamimashiki County, about 30 minutes by car from the center of Kumamoto City, to report on the situation. The town had already been severely damaged by the earthquake on March 14, and the second quake caused even more damage, leaving a devastation that made one want to cover one’s eyes.

The first floors of many houses were crushed, traffic lights were tilted, and some roads caved in several meters. Twenty people were killed. Two thousand buildings were damaged. The road to Minamiaso Village, a 40-minute drive from Mashiki Town, was also cracked in many places. In the village, many buildings were engulfed by landslides, the Aso Ohashi Bridge collapsed, and the road leading to the center of the village was cut off, leaving many victims isolated. We spoke to a man who had returned to check on his home.

He said, “I was fine, but my mother, who was sleeping at home, was pushed against a shelf and hurt herself. The hospital was not functioning due to the power outage, and I was only given painkillers, but I could not be hospitalized. The shelter was also full and we couldn’t get in. My mother still has three broken ribs, but she is living in the car with me.

In Kumamoto Prefecture, the number of earthquakes measuring 1 or higher on the Japanese seismic intensity scale has reached over 700 in a week since March 14, and another earthquake measuring 5 or higher on the Japanese seismic intensity scale occurred on the evening of March 19. People were only growing anxious about the earthquakes that seemed to have no end in sight.

Uneasy to face due to “disturbing activity on an active fault line

The earthquake caused 278 deaths (50 direct and 228 disaster-related), 8,667 houses were completely destroyed, and 183,882 people were evacuated. Due to the confusion at evacuation centers immediately after the earthquake, it was noted that 80% of the deaths were disaster-related, and care for evacuees staying in their cars became an issue.

After the main quake occurred on March 16, the earthquake-stricken area expanded from around Kumamoto City to the Aso region and then to the central part of Oita Prefecture, extending 150 km in a belt. The Japan Meteorological Agency named the series of seismic activity that began on March 14 the “Heisei 28 Kumamoto Earthquake. Although seismic activity gradually subsided, by April 2005, one year later, aftershocks of intensity 1 or higher had occurred approximately 4,000 times. This number far exceeded the 999 aftershocks of the Chuetsu Earthquake in Niigata Prefecture, which was an inland-type earthquake.

It was the first time in recorded history that two magnitude 7 earthquakes occurred at the same location, with the second being larger in magnitude than the first, and the first time a magnitude 7 earthquake was observed in Kyushu.

Ten years have passed since the earthquake, and reconstruction has progressed in the affected areas. Kumamoto Castle, which had been a symbol of the damage caused by the earthquake, had its keep and long walls restored in 2009. The number of visitors to the park, which had temporarily dropped to 120,000, has recovered to 1.42 million, just before the pre-earthquake level. However, the turrets and stonewalls have not yet been restored, and in particular, more than 100,000 stones need to be relaid for the stonewalls, which will take many more months. The complete restoration is scheduled to be completed in fiscal year 1952.

The Kumamoto earthquake is believed to have been caused by misalignment of the Hinagu Fault Zone and the Nunagawa Fault Zone, which extend to the southwest of Kumamoto City. Some scholars familiar with crustal deformation have pointed out that the earthquake could be linked to activity along the Median Tectonic Line fault zone, which stretches from Kashiba, Nara Prefecture, to off the coast of Iyo City, Ehime Prefecture. In fact, on September 1, 1596, a 7.0-magnitude Keicho-Bungo earthquake occurred in Oita Prefecture, which lies to the west of the Median Tectonic Line fault zone. Four days later, the M7.5 Keicho-Fushimi earthquake occurred in the Kinki region, which lies to the east of the fault zone.

Yet another seismologist had long predicted that several active faults inland would be stressed by old wounds in the active faults, causing earthquakes as a precursor to a Nankai Trough earthquake. These active faults were the Hinaku Fault Zone, which caused the Kumamoto earthquake, “the area from the center of the Kii Peninsula in the Median Tectonic Line Fault Zone to Wakayama City in the west,” and “the eastern margin fault zone of the Nara Basin. As if to support this theory, an earthquake of maximum intensity 4 was recorded in Wakayama Prefecture at the eastern end of the Median Tectonic Line on April 1, ’16.

It is believed that there is no direct relationship between the Kumamoto earthquake and the Nankai Trough earthquake. However, as the seismologist mentioned earlier, the occurrence of earthquakes caused by active faults is said to be a sign that a Nankai Trough earthquake is near. Nine years after the aforementioned Keicho-Bungo earthquake, a major earthquake centered on the Nankai Trough occurred.

Even though 10 years have passed since the Kumamoto earthquake, we must not forget that the next major earthquake could come as early as tomorrow.