For the latter one , we review some recent progresses for systems with both high-order and low-order dissipations . Theoretical and numerical investigations reveal the mechanism and the complex pattern evolving from the nonlinear interaction between dissipations and ellipticity .
Astronomical factor makes the earth 's inner core to vibrate periodically , makes the earth 's orbit , the earth 's volume , the earth 's ellipticity , speed of the earth 's revolution and speed of the earth 's rotation to change periodically , it is the external cause of the intermittent energy liberation .
There are many factors concerning with the earth 's free oscillations , such as the earth 's lateral heterogeneity and radial heterogeneity , self-rotation , ellipticity , anisotropy , anelasticity and focal mechanism , together with other factors such as tidal and atmosphere pressure effects .