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, earthquakes
are more likely on shallow thrust faults near the edges of continents
and in (underwater) subduction zones. Lunar or solar eclipses
represent, of course, special cases of full and new moon, but do not
cause any special or different tidal effects from full and new moon.
Earth tides (Earth's surface going up and down by a couple of
centimeters) and especially ocean tides (surface of the ocean going up
and down by a meter or more) raise and lower the confining pressure on
shallow, dipping faults near continental edges and in subduction zones.
When the confining pressure is lessened, the faults are unclamped and
more likely to slip. The increased probability is a factor of ~3 during
high tides. But you must stop are realize that the background
probability is, in general, very low in a given place and year
(fractions of a percent), so that raising this tiny probability by a
factor of 3 during high tides still results in a very tiny probability.
There have also 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)
To see locations of current major earthquakes, go the Hazards Viewer and click on one of the Earth globes on the right hand side.
Poll
1. | Tokyo | 68 |
2. | Los Angeles | 25 |
3. | Manila | 18 |
4. | Bandung | 17 |
5. | Santiago | 16 |
6. | Nagoya | 9.4 |
7. | Osaka | 9.4 |
8. | Jakarta | 9 |
9. | Lima | 8 |
10. | Chengdu | 7.5 |