Detection of Shallow Tectonic Tremors in Hyuga‐nada, Nankai Trough, Using the Newly Established N‐Net OBS Network

Abstract Monitoring tectonic tremors is crucial for understanding stress release in subduction zones and assessing megathrust earthquake risk. The Hyuga‐nada region, at the western edge of the Nankai Trough, Japan, provides a natural laboratory for investigating links among slow earthquakes, megathrust events, and complex subduction structures. To better understand these interactions, we detected shallow tectonic tremors by applying our machine‐learning workflow to newly established offshore N‐net data. Between July 2024 and September 2025, two major tremor episodes occurred: one immediately after the August 2024 7.0 earthquake and another 3 days before the January 2025 6.7 event. Several tremors migrated concurrently with seismicity, suggesting that slow‐slip transient promoted stress transfer along the plate boundary. Tremor activity was concentrated in fluid‐rich plate‐boundary zones but inactive in drained areas, indicating that structural heterogeneity regulates shallow slow‐earthquake dynamics in Hyuga‐nada. These findings provide new insights into slow‐earthquake mechanics.