Multitimescale Anomalies of the Precursory Scale Increase (Ψ) Prior to the 1975 Ms 7.3 Haicheng Earthquake

The 1975 Ms 7.3 Haicheng earthquake, notable for its numerous short-term precursors and successful public warning, provides a unique case to test precursory scale increase (Ψ) theories. Here, we systematically analyze the seismicity preceding the Haicheng earthquake using a composite catalog that combines pre-1970 events with post-1970 events. An automated Ψ detection algorithm is applied to identify statistically significant Ψ anomalies at both short and long timescales preceding the mainshock. We compare these patterns with cumulative Benioff strain and the load–unload response ratio. The results reveal coherent Ψ anomalies before the Haicheng mainshock at both short and longer timescales, suggesting a potential linkage between seismic acceleration, stress loading–unloading behavior, and cumulative energy. These findings provide new insights into the multitimescale preparation of the Haicheng earthquake and highlight the potential value of Ψ for medium-term earthquake forecasting.