  The applicability of the linear theory of elasticity to the Moon has been
studied. As a criterion was taken the smallness of the strain tensor. The
elastic moduli are obtained from the data of the project "Apollo". The pressure
was calculated in the framework of the model of a homogeneous solid sphere
under the action of its own gravity. The strain tensor trace is of the order
$0.02$, which indicates the applicability.
  The strain tensor in the body of the Moon is calculated taking into account
the self-gravity and the Earth's tidal potential. Respectively the free energy
density is calculated. Since the axis of the Moon rotation has its own non-zero
declination to the ecliptic plane, the tidal potential variations take place
during the rotation of the Moon around the Earth.
  The estimation of the corresponding free energy density variations are made.
Their dependence on the depth exhibit qualitative agreement with the data of
depth dependence in the energy of deep moonquakes obtained in the project
"Apollo."
  Integral estimations of variations in the free energy for the year shows that
it is many orders of magnitude greater than estimates of energy for the year of
deep moonquakes energy. Thus offering an answer to the fundamental question:
where is the source of energy released in the deep moonquakes.
