Seismicity velocity jump

Abstract The well-known features of the Earth s crust are interpreted as the result of rock fracturing under deep thermodynamic conditions. For this aim, triaxial failure data are scaled up to the crust taking into account temperatures and rock types. The critical depth of hydraulically permeable cracks coincides with the Mohorovicic boundary and that relates to the crust genesis. The annihilation of a crack system at this depth is in accordance with seismic velocity jump known from geophysical exploration. The features of crust floors as well as total thickness, fault inclination, etc, are explained by the suggested mechanical approach. 

Shearer P. M. and Flanagan M. P. (1999) Seismic velocity and density jumps across the 410- and 660-kilometer discontinuities. Science 285, 1545-1548. 

The Moho was discovered by reflection of seismic waves that corresponds to the velocity of P-waves increase up to 8.2 km/s. Let us show that the crack net annihilation leads to the necessary jump from the values 6-7 km/s typical for the lower crust which itself is often LVZ huge layer. 

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