Observation of an 18.1-Minute Precursory Nucleation Window in Fault Damage Zone: Topological Phase-Space Dispersion (θ) at Milun Fault

We report the detection of an 18.1-minute precursory nucleation window preceding the 2024-04-03 M7.4 Hualien earthquake, observed in 200 Hz pore fluid pressure (Pf) data from the Milun Fault Integrated Groundwater Observation System, Taiwan. Key Results T-1086s (18.1 min) onset: P424 θspread baseline 1.5049 ± 0.0508, threshold (2σ) 1.6065, peak 1.6429 at T-156s (z=2.7σ) θ-space decoupling: P424×P464 coupling increases 4× in the 10 minutes before rupture (0.0809 → 0.3264) EffRank singularity: At T-27s, EffRank peaks at 2.977 with θ₁=6.3° (critical opalescence) Coseismic isolation: 37× pressure asymmetry (23.74 vs 0.64 bar) confirms flow compartment boundaries Cross-event validation: D₁ precursor signal reproduced in 7/7 Taiwan earthquakes with 0/3 control day false positives Methodological finding: Topological measurements (θ) uniquely sensitive to micro-changes; dCor/Pearson fail to detect pre-seismic onset Physical Interpretation The observed sequence constitutes a complete fluid-driven nucleation chain: dilatancy → Pf drop → compartment decoupling → critical slowing down → rupture, observed at temporal resolution unprecedented in borehole Pf monitoring. Dataset Marginingsih, A. S., Wang, S.-J., Ma, K.-F., & Lin, Y.-Y. (2026). Mendeley Data, CC BY 4.0 — 10.17632/dn4338tv9g.2