Earthquake clustering relative to lunar phases in Taiwan

Abstract

The occurrence of local seismicity recorded in Taiwan for the period of 1973-1991 was converted to lunar time to reassess the notion that some earthquakes may be triggered by tidal forces. The abundant seismicity on the basis of lunar time provides not only sufficient data for statistical analysis but also the most direct and reliable estimation of tidal effects on earthquake triggering. Significant clustering of smaller earthquakes (2.5 5) and lunar phases indicates that larger earthquakes are barely induced by tidal forces, but predominantly by tectonic forces. No clear correlation between micro-earthquakes (ML<2.5) and lunar phases suggests that, in addition to tectonic and tidal forces, their occurrence must be primarily associated with other factors.