Iwato Log: Tsukahara Kofun Cluster and the Kumamoto Earthquake, a Place Where Two Tremors Overlap
The burial mounds are shaking.
At 16:27 on July 28, 2026, an earthquake with a magnitude of 7.1 occurred in the Kumamoto region of Kumamoto Prefecture. The epicenter was at 32.6 degrees north latitude and 130.7 degrees east longitude, at a depth of approximately 16 km. A maximum seismic intensity of 7 was observed in Uki City and Hikawa Town, and the Japan Meteorological Agency named this the '2026 Kumamoto Earthquake' (Reiwa 8 Kumamoto Earthquake). (Japan Meteorological Agency)
And even after entering August, this focal region has continued to shake. In the early hours of August 9, an earthquake with a magnitude of 3.0 and a maximum seismic intensity of 1 occurred in the Kumamoto region of Kumamoto Prefecture. Looking at the map of the epicenter, it overlaps directly on top of the Tsukahara Kofun Park in Uto City.
In the previous Iwato Log, I recorded this series of tremors as a question of time: 'Has the solar calendar begun to revolve?' This time, I would like to record the 'memory of the land' that overlaps in the same focal region—the Tsukahara Kofun Cluster.
1. What is the Tsukahara Kofun Cluster?
The Tsukahara Kofun Cluster is one of the largest kofun (burial mound) clusters in Kyushu, spanning Uto City and Jonan Town in Kumamoto Prefecture. It is a burial ground that was used over a remarkably long period, from the Jomon period through the Yayoi period and into the Kofun period (6th to 7th centuries). A total of approximately 500 graves of various types, including square-shaped moated graves, round burial mounds, and keyhole-shaped burial mounds, have been identified, with 77 currently restored and open to the public.
In 1972, when these ruins were discovered during the construction of the Kyushu Expressway, a method was adopted for the first time in Japan to pass the expressway through a tunnel beneath the kofun cluster in order to preserve the ruins without destroying them. In other words, this land is a rare place where modern infrastructure and ancient burial grounds physically overlap.
Within the cluster is a keyhole-shaped burial mound called the Hanamizuka Kofun (46.2m in total length, built between the late 6th and early 7th centuries).
2. In 2016, this burial mound also shook.
Records remain that the Hanamizuka Kofun was actually damaged during the 2016 Kumamoto Earthquake and was subsequently restored.
In other words, this kofun cluster is a place that has directly received the shaking of the same focal region in both the 2016 earthquake and the 2026 earthquake.
However, regarding the specific damage sustained by the Tsukahara Kofun Cluster and the Hanamizuka Kofun due to the 2026 Reiwa 8 Kumamoto Earthquake, I have not been able to confirm primary sources at this time. As with the previous log, I will hold this as 'unconfirmed' until it can be verified.
3. The Nameless Mound
At Aso Shrine, there is a deity named Takeiwatatsu-no-Mikoto, and the Otaue Shinko-shiki (rice planting ritual) to worship that deity was held on July 28.
The Tsukahara Kofun Cluster has no such name.
The people buried in the more than 500 graves are thought to be local leaders whose names were not recorded in the Kojiki or Nihon Shoki, nor in the Fudoki. Unlike shrines that have a presiding deity, the story of 'who is buried here' remains hidden.
This is different from the structure of 'deities being layered and overwritten' that I have seen in previous Iwato Logs. In the Tsukahara Kofun Cluster, the names that would be the subject of overwriting were not recorded from the very beginning.
A land that was not "hidden," but "unnamed." There, the power from the same epicenter has reached twice.
4. Direction as seen from Amagi
Calculating based on the Amagi-san origin (34.920°N, 139.018°E), the results are as follows.
2026 Kumamoto Earthquake Mainshock (32.6°N, 130.7°E): Direction 253.8° (WSW), distance approx. 810.8 km
Tsukahara Kofun Park (32.6935°N, 130.7089°E): Direction 254.5° (WSW), distance approx. 806.3 km
Earthquake in the early hours of August 9 (32.7°N, 130.7°E): Direction 254.5° (WSW), distance approx. 806.9 km
The difference in direction between the mainshock and Tsukahara Kofun Park is a mere 0.7 degrees. As for the August 9 earthquake and Tsukahara Kofun Park, they are at almost the exact same direction and distance.
This entire area lies on the axis that has been recorded in previous Iwato Logs as the "WSW 254° axis." This means that two M7-class earthquakes have occurred on the same axis, 10 years apart, in 2016 and 2026.
5. The current layers
Layer 1 — Earthquake
July 28, 2026, 16:27, Kumamoto Prefecture, Kumamoto region, M7.1, Seismic Intensity 7 (mainshock). An M3.0 aftershock also occurred in the same area in the early hours of August 9. (Japan Meteorological Agency)
Layer 2 — Kofun
Tsukahara Kofun Cluster, one of the largest in Kyushu. From the Jomon to the Kofun period, totaling about 500 burial mounds. A site preserved by routing an expressway through a tunnel.
Layer 3 — Overlap with 2016
Hanamizuka Kofun, damaged and restored during the 2016 Kumamoto Earthquake. Damage from 2026 remains unconfirmed and pending.
Layer 4 — Name
Aso has the name Takeiwatatsu-no-Mikoto. The Tsukahara Kofun Cluster has no name for those buried within.
Layer 5 — Direction
As seen from Amagi, the mainshock, the Kofun Park, and this latest aftershock all overlap almost perfectly on the WSW 254° axis.
Postscript: The Iwato that has not yet opened
The Tsukahara Kofun Cluster is not a place that was "discovered" by an earthquake. It is a place that was discovered by chance during expressway construction, and has continued to shake with every earthquake since.
A land without a name has been struck by major earthquakes twice, 10 years apart, on the same directional axis.
Does this mean something, or are we just trying to find meaning in it?
Beyond that point, it has not yet opened.
I will pause the Iwato Log here.