Stress field

About: Stress field is a research topic. Over the lifetime, 11926 publications have been published within this topic receiving 226417 citations.

Is there a genetic relationship between selected regional joints and contemporary stress within the lithosphere of North America

Abstract: On the Appalachian Plateau of New York, ENE striking joints parallel the mid-continent contemporary stress field and do not correlate with other structures. Joints within Ohio, Indiana, Michigan, and West Virginia also parallel the mid-continent maximum horizontal compression as indicated by hydraulic fracture measurements. In northern Indiana, where the contemporary stress field deviates significantly from the orientation of the mid-continent stress, the attitude of the joints deviates accordingly. In addition to joints, structures on several scales from subcontinent size fracture systems to microfabrics in shales apparently parallel the mid-continent stress field. From this I conclude that these joints are mode I cracks whose orientation corresponds to the contemporary tectonic stress field. In itself, the formation of these structures constitutes a tectonic event that has often been overlooked in favor of tectonic events that produce the more spectacular but less pervasive faults and folds.

A Bayesian approach to estimating tectonic stress from seismological data

Abstract: SUMMARY Earthquakes are conspicuous manifestations of tectonic stress, but the non-linear relationships between the stresses acting on a fault plane, its frictional slip, and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress. Moreover, observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations. However, by assuming that each earthquake in a small volume of the crust represents a single, uniform state of stress, the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated. Here, we outline a probabilistic (Bayesian) technique for estimating tectonic stress directions from primary seismological observations. The Bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation. We show our Bayesian formulation to be equivalent to a well-known analytical solution for a single, errorless focal mechanism observation. The new approach has the distinct advantage, however, of including (1) multiple earthquakes, (2) fault plane ambiguities, (3) observational errors and (4) any prior knowledge of the stress field. Our approach, while computationally demanding in some cases, is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters, such as seismic anisotropy and geodetic strain rate observations, and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations.

Mixed mode near-tip fields for cracks in materials with strain-gradient effects

Abstract: Large strain gradients exist near the tip of a crack due to stress singularity. The strain-gradient effect becomes significant when the size of the fracture process zone around a crack tip is comparable to the intrinsic material length, l , typically on the order of microns. Fleck and Hutchinson's [(1993) A phenomenological theory for strain-gradient effects in plasticity. J. Mech. Phys. Solid 41 , 1825–1857], strain-gradient plasticity theory is applied to investigate the asymptotic field near a mixed mode crack tip in elastic as well as elastic-plastic materials with strain-gradient effects. It is established that the dominant strain field is irrotational. For an elastic material, stresses and couple stresses have the square-root singularity near the crack tip, and are governed by three variables (two for mode I and II stress fields, and the third, resulting from higher order stresses, for the couple stress field). Stresses ahead of a crack tip in elastic materials with strain-gradient effects could be more than 50% higher than their counterparts in materials without strain-gradient effects. For an elastic-power law hardening strain-gradient material, an analytical solution is obtained. The mixed mode stress field in strain-gradient plasticity is the linear superposition of their counterparts in mode I and II. The angular distribution of stresses and couple stresses for several near-tip mode mixities clearly indicate that the new near-tip field in strain-gradient plasticity differs significantly from the HRR field. Stresses ahead of a crack tip in elastic-plastic solids with strain-gradient effects could be more than 2.5 times their counterparts in the HRR field. The asymptotic analysis compares favorably with available finite element results. The relevance of this solution to materials, in particular the size of the dominant zone, is discussed.