Effect of a Tidal Wave Caused by Large Gliding Satellite on Formation of 220 km Seismic Boundary and Split of the Mantle into Blocks
The movement of a large satellite around a model planet, which is a thick spherical layer of a heavy, perfect liquid with a solid nucleus, is being discussed. The tidal disturbance caused by the satellite is propagated by long gravity waves. When the satellite is gliding along the layer surface the energy and orbital period decrease, and the tidal height and period of free gravity waves supporting the tide growth increase. To maintain the tide the orbital period should not be less than the period of free long gravity waves. The value of static tide is assessed for the case when orbital period and free gravity waves expending over the surface of spherical liquid layer periods coincide. When this condition is met gliding becomes impossible and the satellite fully submerges. With regard to the Earth, movement of the satellite projection is supersonic for the material composing the mantle above a certain horizon, and subsonic for underlaying horizons. The pressure of the tide bulge has effect on the entire lower layer and on a narrow front area of shock wave in the upper layer. Therefore, a considerable horizontal stress occurs at the abovementioned horizon. When the stress exceeds the shear strength limit, the upper layer of the mantle starts to move at a finite velocity in relation to the lower mantle. A melt forms in the friction layer, so the velocity of longitudinal seismic waves decreases. The boundary of supersonic and subsonic velocities gradually lowers increasing the melt layer thickness and forming an abrupt jump in seismic wave velocities. After the boundary reaches the horizon at 220 km, the satellite submerges into the mantle. This is the reason why at present moment, after the melt solidification there is a low velocity zone of seismic waves in the upper mantle and a 220 km seismic boundary.
KeywordsAsteroid Satellite Spherical layer Ideal fluid Gliding Long gravity waves Earth’s mantle Tide Seismic waves velocity Melt Seismic boundary Low velocity zone of seismic waves
The work was done with the support of Grant RFBR No. 16-01-00466.
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