Strong earthquakes correlate closely with lunar phases in North China and its seismic belts. The times of most of the strong earthquakes cluster around the times of new moon in North China region and the Hebei Plain, Hehuai, as well as southern Yellow Sea belts. Most of the,events seem to occurrence around the times of the first quarter in the Tanlu and Fenwei belts. Based on the structures of the crust-upper mantle for the source regions of some strong earthquakes in North China, possible mechanism of tidal triggering earthquakes, called triggering model of upwelling fluids driven by the tidal forces, was discussed. Its main point as follows: (I) The essential condition of strong earthquakes preparation is that the fluids exist in the crust and upper mantle. (2) The speeding upwelling of the deep fluids is possible. (3) The tidal force seems to be main one triggering deep fluids speedy upwelling. (4) The deep fluids trigger the occurrences of strong earthquakes by means of some nonlinear mechanism, such as stress corrosion or Rebinder effect.
