In the paper double seismic zones are discussed as a phenomenon
confirming penetration of oceanic lithosphere through the mantle as
solid and extremely hard medium. Formation of such medium has been
performed by solidification of Earth from core-mantle boundary upwards.
Lower mantle formed under extremely high pressure prevents any
earthquakes. Upper mantle is suitable for formation of embrittlement and
earthquakes in double seismic zones. Continental lithosphere overriding
oceanic lithosphere forms subducton zones firmly anchored in mantle.
Deeply steeping subduction zones penetrate mantle burning its way by
melting probably as far as through core-mantle boundary. Oceanic
lithosphere grows in midocean ridges with half speed of the front of
plate. Driving forces are tides. Movements of plates confirm hotspot
tracks. Hotspots are probably of meteoric origin. They penetrate through
mantle in same way as subducton zones. Material created in penetration
moves upwards by buoyancy and during its subsidence creates hotspot
tracks over 10 000 km, however their penetration as far as coremantle
boundary is not proven.