Figure 1 – Spatial evolution of cumulative vertical displacement from Sentinel-1 MT-DInSAR 3.2 Zone stratification and deformation-rate statistics To support spatial interpretation and enable zone-aware modelling, the 85 monitoring points were grouped into four zones based on dam geometry and structural position: Crest, Toe, East, and West. Table 3 summarises the zone-level statistics of vertical deformation rate. The West and Crest sectors show the highest mean deformation rates and the widest dispersion, indicating more heterogeneous deformation behaviour, likely driven by active construction, material variability, and staged loading conditions typical of TSF operations. The Toe is comparatively, whereas the East shows intermediate rates with moderate variability. A notable exception in the time series occurs on 5 January 2025, when the mean deformation increments across the network reached 34 mm, markedly higher than the preceding and following acquisitions. Because this anomalous increment was observed in more than 90% of monitoring points, it is interpreted as an acquisition-wide InSAR artefact rather than a genuine short-term deformation event. In practice, such scene-wide spikes are typically associated with residual atmospheric phase delays, temporal decorrelation, or phase-unwrapping errors, particularly under low-coherence conditions (Yunjun et al., 2019). Table 3 – Zone-level statistics of vertical deformation rate magnitude (mm/day) Crest Toe West East N. points 14 9 32 30 Average -0.180 -0.072 -0.193 -0.121 Maximum -0.056 -0.051 -0.021 0.001 Minimum -0.296 -0.114 -0.324 -0.272 Standard deviation 0.078 0.023 0.090 0.070 3.3 Sector-based weather-deformation analysis To evaluate the influence of rainfall on short-term surface deformation, 12-day rainfall totals were aligned with the Sentinel-1 acquisition intervals, and high-rain periods were defined as values above the 90th percentile of the record (>177.7 mm per 12-day interval; 17 of 166 intervals). Figure 2 shows the sector-scale distributions of mean absolute deformation rates under high-rain and other intervals. Strong overlap is observed across all sectors, indicating that high rainfall did not produce a consistent increase in short-term deformation. The clearest contrast is spatial rather than meteorological: the West and Crest sectors show the widest distributions and highest uppertail values, whereas the Toe shows the narrowest spread. Importantly, this analysis considers
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