The rotation of the Moon around the Earth, like the rotation of the latter around the Sun, does not occur in a circle, due to which they periodically approach and move away from each other. As a result of this interaction, forces arise that are capable, for example, of pulling our atmosphere and oceans towards the Moon, creating ebb and flow. Recently, American geologists have found that this phenomenon can affect the state of the Earth's interior.
A team of scientists led by Paul Johnson of the Los Alamos National Laboratory in the United States investigated seismic activity in the state of California near the San Andreas Fault, where weak tremors or earthquakes occur almost daily.
Earlier, experts from the US Geological Survey found that the stress of the rocks in this place and the frequency of tremors naturally change at different times. Johnson and his colleagues decided to check whether this does not depend on the change in the position of the moon in relation to our planet.
They correlated the strength of the tremors, the frequency of earthquakes and the speed of the oscillations with the position of the Moon relative to the Earth. Calculations have revealed the dependence of these seismic processes on a 14-day cycle, which is half of the classical one and to which the action on the Earth of the lunar attraction and similar forces generated by the interaction with the Sun is subordinated.
It is noteworthy that, contrary to the expectations of scientists, earthquakes more often occurred when tidal forces weakened. So far, geologists have no answer to this question, but it probably lies in the peculiarities of the interaction of lunar and earthly forces.
The research article was published in the journal PNAS.