Couldt the fluid or magma driven crack born the tensile one?
© Guterman V.G., Khazan Ya.M.
The paper presents the results of numerical and physical modeling of horizontal fluid driven crack propagation. Both the numerical and physical modeling testify that a quasiequilibrium fluid driven crack propagates as a tensile one. If however the internal overlithostatic pressure exceeds the equilibrium value so that both tensile and shear strengths are exceeded an edge shear crack forms resulting in a seismic event. Since the equilibrium pressure decreases with increasing crack length the probability of the edge shear crack formation due to the internal pressure fluctuations increases in the course of the crack propagation in agreement with the basic assumption of the intrusive model of earthquake preparation. It is shown also that the structure of the process zone at the crack tip changes with depth. In the upper crust it is elongated in the crack plane and the fracturing occurs through the tensile in this cohesive zone. In the middle crust and below a macroscopic zone elongated perpendicularly to the crack plane forms, and the fracturing occurs through the shear along it. <<back 
