FAQ - Common Myths about Earthquakes

Q: Can the position of the moon or the planets affect seismicity?

A: 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

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. (UC Berkeley)

For further information, see:
Gravitational Forces - University of California, Berkeley, Seismological Laboratory

« Previous FAQ | All FAQ's | All FAQ Categories | Next FAQ »