Rock deformation and fracture mechanics
Understanding how fractures originate, propagate, and terminate in the Earth interiors is of great importance for many fields of science and engineering (e.g., the earthquake source physics, structural geology, volcanology, mining, petroleum exploration). My work has involved generation and testing of predictive models of fracture growth in crystalline materials under ambient stresses corresponding to the in situ conditions in the Earth. One of the important outcomes of this work has been a demonstration of the inadequacy of the standard Linear Elastic Fracture Mechanics (LEFM) models in describing rock failure at depth (more specifically, when confining pressure exceeds the intrinsic rock strength). Using physicallly sound models that explicitly consider inelastic deformation (e.g., the Barenblatt-type model of a cohesive zone) at the crack tip, we demonstrated for the first time that at high confining pressures the rock tensile fracture energy is not a material property and that it may depend on the near-tip stress field and overall loading configuration. This result is unexpected because propagation of Mode I (i.e., tensile) cracks requires absolute tension at the crack tip, and therefore the rock that fails at the crack tip should not be "aware" of ambient compression. This work may be a starting point for explaining various scalings of the rock fracture energy with the crack size and/or the ambient stress field that have been inferred from field observations.
For more details please see these papers:
- Fialko, Y., Y. Khazan, and M. Simons, Deformation due to a pressurized horizontal circular crack in an elastic half-space, with applications to volcano geodesy, Geophys. J. Int., 146, 181-190, 2001 (download PDF)
- Fialko, Y., M. Simons, and Y. Khazan, Finite source modeling of magmatic unrest in Socorro, New Mexico, and Long Valley, California, Geophys. J. Int., 146, 191-200, 2001 (download PDF)
- Fialko, Y., and M. Simons, Deformation and seismicity in the Coso geothermal area, Inyo County, California: Observations and modeling using satellite radar interferometry, J. Geophys. Res., 105, 21,781-21,794, 2000 (download PDF)