Probing the Earth's strength: Can we measure small stress at high pressure?

Simulating the conditions and processes that occur in the Earth's deep interior has been a major goal of experimental geophysics since the 1920s. In particular, pioneers such as P. W. Bridgman, David Griggs, Hugh Heard, Mervyn Paterson, William Brace, and their colleagues sought to establish the basic relations between differential stresses and rock and mineral deformation under pressure-temperature conditions that favor such inelastic processes as brittle fracture, frictional sliding, plastic deformation, and dynamic metamorphism. This work has been applied to diverse problems in the Earth sciences, including the physical nature of earth quake sources, the forces that drive and resist plate movement, deformation under partial-melting conditions at the tops of mantle plumes, the flexure of the lithosphere, post-glacial rebound, and the origin of the preferred orientation of minerals and the resultant seismic anisotropy and metamorphic textures.