Can the position of the moon or the planets affect seismicity?
The moon, sun, and other planets have an influence on the earth in the form of perturbations (small changes) to the gravitational field. The relative amount of influence is proportional to the objects mass, and inversely proportional to the third power of its distance from the earth. The stresses induced in the earth by an extraterrestrial mass are proportional to the gravitational field gradient dg( r ) / dr and NOT to the gravitational field g( r ). g( r ) = GMm / r^2 thus: dg( r ) / dr = -2 * g( r ) / r = -2GMm / r^3 Many studies in the past have shown no significant correlations between the rate of earthquake occurrence and the semi-diurnal tides when using large earthquake catalogs. Several recent studies, however, have found a correlation between earth tides (caused by the position of the moon relative to the earth) and some types of earthquakes. One study, for example, concludes that during times of higher earth and ocean tides, such as during times of full or new moon, earthqua
