The stress state at a point in the crust can be specified by describing the orientation and magnitude of the three principal stresses. It is not uncommon in structural geology that a depiction of the three principal stresses is used to implicitly or explicitly infer a homogenous stress field within the crust. This is an approximation or an assumption, and it is useful to remind ourselves that homogenous stress fields are a simplifying fiction. Stress fields exist due to increasing overburden with depth (lithostatic gradient), due to small and large scale topography, due to inhomogeneties and discontinuities in the crust (e.g. faults), due to openings (tunnels), due to intrusions, and due to variable plate boundary conditions. Stress fields in turn determine the patterns of structures that result. It is therefore insightful to consider some stress fields.

Student entries on stress fields (forthcoming):

** Some relevant references: **

- Coblentz, D. D. and Richardson, R. M., 1995, Statistical trends in the intraplate stress field; Journal of Geophysical Research, v. 100, #B10, p. 20,245-20,255.
- Cornet, F. H. and Burlet, D., 1992, Stress field determinations in France by hydraulic tests in boreholes; Journal of Geophysical Research, v.97, B, 11,829-11,849.
- Engelger, T., 1993, Stress regimes in the lithosphere; Princeton University Press, Princeton, 457 p.
- Goodman, R. E., 1989, Introduction to Rock Mechanics; John WIley, New York, 562 p.
- Grana, J. P. and Richardson, R. M., 1996, Tectonic stress within the New Madrid seismic zone; Journal of Geophysical Research, v. 101, #B3, p. 5,445-5,458.
- Jaeger, 1969, Elasticity, Fracture and Flow, Chapman and Hall, London, 267p.
- Means, 1976, Stress and Strain, Springer-Verlag, New York, 339 p.
- Miller, D. J., 1996, Topographic pertubations of regional stresses and consequent bedrock fracturing; Journal of Geophysical Research, v. 101, #B11, p. 25,523-25,536.
- Zoback, M. L., and others, 1989, Global patterns of tectonic stress; Nature, v. 341, p. 291-298
- Zoback, M. L. and Richardson, R. M., 1996, Stress pertubation associated with the Amazonas and other ancient continental rifts; Journal of Geophysical Research, v. 101, #B3, p. 5459-5475