Interdecadal seismic periodicity modulated by solar and oceanic variability revealed from Chinese historical documents.

Understanding the interdecadal periodicity of large-scale seismic activities is critical for improving long-term earthquake forecasting, yet it remains constrained by the limited duration of instrumental records. Here we apply high-resolution spectral analysis to a millennia-long catalog of historical earthquakes in China, extending to 1831 BC. The most pronounced seismic activities occurred during the 1620-1630 s AD, a period that coincided with a major regime shift that preceded the collapse of the Chinese Ming Dynasty. High-resolution spectral analysis was performed on the historical dataset to identify robust ~ 10- and ~ 50-year periodicities in seismic frequency. The ~ 10-year periodicity exhibits a significant lagged correlation with solar (sunspot) activity, while the ~ 50-year periodicity aligns with multidecadal variability in solar irradiance, sea level fluctuations, and tropical sea surface temperatures (SSTs). We propose that enhanced solar irradiance modulates the mean state and variability of tropical Pacific climate modes, particularly the El Niño-Southern Oscillation (ENSO), which is associated with changes in inter-basin sea-level gradients and crustal stress regimes. These findings reveal a potential coupling between external solar forcing and internal climate variability in shaping seismic cyclicity at interdecadal scales, offering a novel framework for assessing long-term earthquake risks.