Pre-Seismic Quiescence Detected by K–R Critical Slowing-Down Indicators: Independent Replication in Japan and Chile Subduction Zone Catalogs

We present the K–R excitation–regulation framework — a coupled ordinary differential equation (ODE) system producing Critical Slowing Down (CSD) indicators from rolling earthquake magnitude windows — and demonstrate independent cross-catalog replication of a pre-seismic CSD quiescence signal across two subduction-zone settings. In the Japan USGS catalog (Mc ≥ 4.5, N = 14,501 events, 2000–2022), CSD₅₀ is suppressed − 17.2% to − 20.9% across four consecutive pre-seismic lags (− 14, − 7, −3, − 1 days) before clean M ≥ 6.0 mainshocks (60-day isolation criterion, n = 41). All four lags survive Benjamini–Hochberg FDR correction (p = 0.003–0.005) and permutation test (p = 0.004–0.012). The identical pipeline applied to the Chile USGS catalog (Mc ≥ 4.5, N = 9,150 events, 2000–2024) independently replicates the signal: CSD₅₀ suppressed − 17.7% to − 22.0% across the same four lags (n = 58, all FDR-significant, permutation p ≤ 0.002). Effect sizes are statistically indistinguishable between the two subduction zones. The signal is absent in unfiltered catalogs, and rolling b-value analysis shows no concurrent change at any lag (all p > 0.30), confirming CSD₅₀ captures a signal distinct from frequency-magnitude variation. Controlled synthetic validation identifies the causal mechanism: variance reduction alone produces strong CSD suppression (− 54.3%, p < 0.001); rate reduction alone does not (− 8.5%, p = 0.091). A physically realistic rate+variance scenario (− 38.2%, p < 0.001) matches the observed effect. A pure ETAS control shows CSD increase (+ 28.7%, p = 1.000), confirming no false positives. Rate-and-state friction simulation (Dieterich, 1994) yields − 60.3% suppression during a locking phase (p < 0.0001). Time-shuffle surrogate testing confirms temporal anchoring (p = 0.004). The K–R ODE identifies four seismic regimes (Markov persistence 0.941; S3/S4 hazard ratio 1.77×). CSD₁₀₀ achieves AUC = 0.549 [0.510, 0.590] for M ≥ 5.5 forecasting on the Japan test set (2016–2022), framed as a complementary diagnostic. We do not claim spatial universality, operational forecasting, or deterministic prediction. The cross-catalog replication elevates this from a single-catalog observation to a reproducible seismological finding.