Geomechanics (from the Greek prefix geo- meaning "earth"; and "mechanics") involves the geologic study of the behavior of soil and rock. The two main disciplines of geomechanics are soil mechanics and rock mechanics. The former deals with the behaviour of soil from a small scale to a landslide scale. The latter deals with issues in geosciences related to rock mass characterization and rock mass mechanics, such as applied to petroleum industry or high depths, tunnel design, rock breakage, and rock drilling. Many aspects of geomechanics overlap with parts of geotechnical engineering, engineering geology, and geological engineering. Modern developments relate to seismology, continuum mechanics, discontinuum mechanics, and transport phenomena. In the petroleum engineering Industry, geomechanics is used to predict important parameters, such as in-situ rock stresses, modulus of elasticity, leak-off coefficient and Poisson's ratio. Reservoir parameters that include: formation porosity, permeability and bottom hole pressure can be derived from geomechanical evaluation. The geotechnical engineer or geophysicist relies on various techniques to obtain reliable geomechanical models. These techniques that have evolved over the years, are: coring, log analysis; well testing methods like hydraulic fracturing, and geophysical sonar methods such as acoustic emission.