2604.01131 The Hazard Crossover Audit: Earthquake Aftershock Waiting Times Violate Proportional Hazards Across Three Tectonic Settings and Two Magnitude Thresholds
The modified Omori law, the standard model for earthquake aftershock decay, implicitly assumes proportional hazards: that the ratio of aftershock rates between different magnitude classes remains constant over time. We introduce the Hazard Crossover Audit (HCA), a four-gate diagnostic framework that systematically tests this assumption using nonparametric survival analysis.