The moon, sun, and other planets have an influence on the earth in the form of perturbations to the gravitational field. The relative amount of influence is proportional to the objects mass, and inversely proportional to the square of its distance from the earth. No significant correlations have been identified between the rate of earthquake occurrence and the semi-diurnal tides when using large earthquake catalogs. There have, however, been some small but significant correlations reported between the semi-diurnal tides and the rate of occurrence of aftershocks in some volcanic regions, such as Mammoth Lakes.   _{Your Comment}