Geological Data for Storage Sites
—— Thousand-Year Risk Assessment for Sado and Maui

1. Comparison Summary

2. Sado Island — A 30-Million-Year Continental Island

Geological Structure

Sado Island formed approximately 30 million years ago as part of the Eurasian continent and separated as the Sea of Japan expanded. Its infinity shape comes from the Great Sado Mountains in the north and Small Sado Mountains in the south, connected by the Kunaka Plain. This geological age is orders of magnitude older than volcanic islands like Maui (1–2 million years) or Tahiti (1–3 million years).

Being a continental island matters profoundly. Volcanic islands are born above hotspots, drift with plate movement, and eventually submerge through erosion and subsidence — the Emperor Seamounts northwest of Hawaii are a textbook example. Continental islands, however, are part of continental crust and do not follow this submersion cycle. The fact that Sado has existed as an island for 30 million years is itself proof of its stability.

Earthquake Risk

Sado lies near the Japan Sea eastern margin deformation zone. This zone, near the boundary of the Eurasian and North American plates, has produced the 1964 Niigata earthquake (M7.5), the 2004 Chuetsu earthquake (M6.8), the 2007 Chuetsu-oki earthquake (M6.8), and the 2024 Noto Peninsula earthquake (M7.6).

However, none of these earthquakes had epicenters on Sado itself — they were located on the mainland side or on the seafloor. Recorded shaking on Sado has been intensity 4–5 at most. Active faults have been identified on the island, but there is no record of a major direct earthquake beneath it.

Thousand-year assessment: Strong shaking from an M7-class earthquake is possible. But quartz glass does not break from shaking. Seismic design of the storage facility is the essential countermeasure.

Sea Level Rise Projections

According to the IPCC Sixth Assessment Report (AR6, 2021), global mean sea level rise by 2100 is projected at 0.32–0.62 m under SSP1-2.6 and 0.63–1.01 m under SSP5-8.5. Long-term projections to 2300 suggest the possibility of several meters under SSP5-8.5.

Sado's highest point is 1,172 m (Mt. Kinpoku). Placing a storage facility at 100 m or higher elevation means sea level rise of several meters would have no impact. Coastal settlements may be affected, but the storage site can be positioned to avoid this entirely.

3. Maui — Haleakalā's Dormant Volcanic Island

Geological Structure

Maui is a volcanic island born from the Hawaiian hotspot on the Pacific Plate. West Maui Mountain (Mauna Kahalawai) and Haleakalā are connected by a central isthmus, forming the infinity shape. Geological age is 1–2 million years.

The Pacific Plate moves northwest at approximately 7 cm per year, and Maui is already drifting away from the hotspot. Current volcanic activity is centered on the Big Island to the southeast (Kīlauea, Mauna Loa). This means Maui's volcanic activity is on a declining trend going forward.

Volcanic Risk

The date of Haleakalā's last eruption is debated. The USGS estimates the 1480s–1600s, while some sources record an eruption around 1790. Regardless, over 200 years have passed without eruption, and the USGS Volcanic Threat Assessment (2018 edition) classifies Haleakalā as a "moderate threat."

We must honestly acknowledge that it is "dormant," not "extinct." The probability of Haleakalā erupting within the next 1,000 years is not zero. But even if it does erupt, lava flows follow terrain. Siting the storage facility away from predicted lava flow paths avoids direct damage.

Earthquake Risk

Maui's own seismic activity is low. Earthquakes in the Hawaiian Islands are concentrated on the volcanically active Big Island. Even during the 2018 Kīlauea eruption's M6.9 earthquake, shaking on Maui was minimal.

On a thousand-year scale, large volcanic earthquakes from the Big Island or Pacific Plate intraplate fault activity may cause shaking. But as with Sado, the risk to quartz glass is manageable through seismic facility design.

Sea Level Rise Projections

Haleakalā stands at 3,055 m. Sea level rise vulnerability is limited to coastal areas. However, Hawaiian islands slowly subside as they drift from the hotspot. Maui's estimated subsidence rate is 0.02–0.05 mm per year — extremely gradual, amounting to a few centimeters to a few tens of centimeters over a millennium. Even combining subsidence with sea level rise, the risk of a highland storage facility being submerged is extremely low.

4. Why Two Sites

Neither Sado nor Maui alone is sufficient.

Sado is overwhelmingly superior in geological stability. Its 30-million-year track record speaks louder than any risk model. But earthquake risk from the Japan Sea eastern margin cannot be ignored.

Maui carries inherent risk as a volcanic island. But its trend is one of declining activity as plate movement carries it from the hotspot. And it belongs to an entirely different geological structure from Sado, separated by the Pacific Ocean.

The probability of the same disaster simultaneously destroying both Sado and Maui is vanishingly close to zero.

Planet-scale distribution means driving the correlation of geological risks toward zero. A Japan Sea earthquake does not affect Maui. A Haleakalā eruption does not affect Sado. The geological risks of the two islands are independent.

And even if one site is hit, the physical layer (quartz glass in the owner's hands), national layer (National Diet Library), and private layer (GitHub) preserve data through separate channels. Geological risk is managed as part of a redundant design across three layers and two sites.

5. Limitations of This Assessment

Honestly, no one can accurately predict geological risk a thousand years into the future.

IPCC projections extend to 2100 (at most 2300). Beyond that, uncertainty is too great for scientific consensus. For long-term volcanic eruption prediction, nothing more can be said than "probability distributions based on historical data."

What this essay can demonstrate is this: "Based on the best data available in 2026, Sado and Maui are rational choices as thousand-year storage sites." Nothing more, nothing less.

The 10-year review cycle defined in our technology roadmap applies not only to technology but also to geological data updates. New fault discoveries, revised sea level projections, advances in volcanic monitoring — all will be incorporated every 10 years, and this document updated accordingly.