Radiocarbon Analysis of Seabed Sediments Reveals Hidden Earthquakes near Nankai Trough

Scientists have identified hidden earthquakes near the Nankai Trough off the coast of Japan by analyzing seafloor sediment deposits, reports Nauka.ua. The study, published in the journal Radiocarbon, focused on a 40-centimeter core sampled near the Kumano Basin, an area situated in the forearc basin of the seismically active subduction zone nauka.uaНаука.uanauka.uaOpen source ↗. Tectonic activity was dated by measuring the decay of carbon-14 accumulated in marine organic matter.

Carbon-14 Profiling and Sediment Disturbance

Researchers took samples at intervals of 0.5 to 1 centimeter along the core to evaluate the radioactive decay of carbon-14. The oldest undisturbed layers were reliably dated to 1440 CE. While the sediment appeared visually uniform, isotopic measurements revealed anomalies where older layers were positioned above younger ones, indicating significant physical displacement and mixing of seafloor material.

To ensure that the isotopic discrepancies were not caused by terrestrial sediment washed in by nearby rivers, the team analyzed the ratios of carbon isotopes and the carbon-to-nitrogen ratios. These geochemical signatures confirmed that the disturbed horizons were indeed older marine deposits rather than riverborne influx. The core layers were additionally dated through the presence of microscopic marine organisms known as foraminifera.

Correlation with Historical Seismic Catalogs

By comparing the reconstructed timeline with historical earthquake records, the researchers determined that several mixing events precisely aligned with known major seismic events nauka.uaНаука.uanauka.uaOpen source ↗. Other detected disruptions did not correlate with recorded history, pointing to previously undetected tectonic activity. The authors expect that high-resolution radiocarbon profiling of forearc basins will facilitate the reconstruction of historical megathrust ruptures and tectonic processes beyond Japan.