Abstract: The authors apply the Morishita index IW to analyze the features of the daynigh and seasonal distribution of earthquakes in China. They found that: IW for earthquakes with M≥8 is 1.40 and 1.20, showing sw arm distribution; IW for earthquakes with M≥7 is 1.03 and 1.12, showing the feature of weakly swarming; IW for earthquakes with M≥6 is 0.94 and 1.02, distributed uniformly and sto chastically; IW for earthquakes with M≥5 is 1.01 and 0.99, distributed also uniformly and stochastically. The feature of swarming distribution for strong earthquakes is obvious, and the feature of uniform and stochastic distribution appears in small and moderate earthquakes. The statistical results indicate that occurrence of strong earthquakes in China's inland is mainly concentrated at night.

Key words: Day and night, Season, Morishita index