Stress field

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

Fringe cracks: Key structures for the interpretation of the progressive Alleghanian deformation of the Appalachian plateau

Abstract: Vertical joints in Devonian clastic sedimentary rocks of the Finger Lakes area of New York State are ornamented with arrays of fringe cracks that reveal the complex deformational history of the Appalachian plateau detachment sheet during the Alleghanian orogeny. Three types of fringe cracks were mapped: gradual twist hackles, abrupt twist hackles, and kinks. Gradual twist hackles are curviplanar en echelon fringe cracks that propagate with an overall vertical direction within the bed hosting the parent crack and are found in all clastic lithologies of the detachment sheet. Abrupt twist hackles propagate as planar features in thick shale beds above or below the siltstone beds hosting parent joints. Kinks propagate horizontally as planar surfaces from the tips of parent joints in siltstone beds. The breakdown of the parent joint into either gradual or abrupt twist hackles depends on the orientation and magnitude of the remote stress field, internal fluid pressure, and the elastic properties of the bed. The twist angle of gradual twist hackles is larger in coarser clastic beds, indicating that stress and internal pressure are more important parameters than elastic properties in controlling breakdown. Assuming that the vertical stress axis (S v ) equals 78 MPa at 3 km burial depth, the difference in twist angle between sandstone and shale beds is used to estimate the maximum horizontal stress difference in the shale beds as S H ‐ S h ∪ 2.5 MPa when S H ‐ S h ∪ 12 MPa in sandstone beds. The twist angle of the fringe cracks and the abutting relationships of parent joints give an indication of the overall change in stress field orientation within the detachment sheet during Alleghanian tectonics. These parent joints indicate a regional clockwise stress rotation of Alleghanian age concordant with the twist angle of fringe cracks throughout the western part of the study area. A counterclockwise twist angle in the eastern portion indicates a local stress attributed to drag where no salt was available to detach the eastern edge of the plateau sheet. The clockwise change in stress orientation is consistent with the rotation in stress orientation found in the anthracite belt of the Pennsylvania Valley and Ridge, but is opposite to the sense of rotation in the southwestern portion of the detachment sheet (western Pennsylvania and West Virginia). The two regional rotation domains are separated by the Juniata culmination.

Fatigue crack propagation in biaxial stress fields

Abstract: The propagation of fatigue cracks in notched and un-notched biaxially stressed plates is investigated. The rate of propagation is found to be affected by both the stress field associated with the notch and the biaxial stress state of the bulk material. It is found that the propagation rate of a crack from a notch may be predicted by the use of a theoretical notch contribution factor in conjunction with propagation data for a crack in un-notched material.

Sequential hydraulic fracturing of a subsurface formation

Abstract: A subsurface formation having original in-situ stresses that favor the propagation of a horizontal fracture is penetrated by a borehole. A first fracturing fluid containing a propping material is pumped through the borehole and into the formation at a first depth to propagate a horizontal fracture which alters the in-situ stress field. The pumping of the first fracturing fluid is stopped and a second fracturing fluid is pumped through the borehole and into the formation at a second depth to form a vertical fracture within the field of altered in-situ stress.

Effects of density contrasts on the orientation of stresses in the lithosphere: Relation to principal stress directions in the Transverse Ranges, California

Abstract: The influence of stresses arising from horizontal density contrasts on the orientation and relative magnitudes of principal stresses in an otherwise uniform lithospheric stress field is investigated. A simple model is constructed, in which a local deviatoric stress due to a density anomaly, embedded within or just below the lithosphere, and a regionally constant deviatoric stress field are each approximated by biaxial tensors. The net stress field is obtained from the sum of the two. Both the relative magnitudes of principal stresses and the magnitude of the angular difference in principal stress direction of the summed tensor compared with that obtained in the absence of buoyancy forces depend on two parameters. The first is the ratio τ/τ′, where τ is a measure of the magnitude of the regional deviatoric stress and τ′ is the magnitude of the stress arising from buoyancy forces associated with the density anomaly. The second parameter is the angle between the trend of the density anomaly and the direction of maximum compressional stress that obtains in the absence of any perturbation by the local buoyancy forces. The directions of the principal axes of the total stress field are found to differ by up to 90° from those of the reference stress field. The model is applied to the Transverse Ranges, California, where the observed 23° difference in orientation of principal horizontal compressive stress compared with the principal compressive stress direction in central California constrains the predicted value of τ/τ′ to be approximately −0.4. This is consistent with an independently calculated range of τ/τ′ in which τ′ is inferred from seismological constraints on the magnitude of density variations underneath the Transverse Ranges and τ is inferred from observations of heat flow along the San Andreas fault in central California. The agreement between the two estimates of τ/τ′ supports the hypothesis that the observed differences in horizontal principal stress orientation in California can be explained by the combined influence of a local negative buoyancy force under the Transverse Ranges and a regional stress field associated with transcurrent deformation within the Pacific-North American plate boundary zone. The observed counterclockwise angular difference in principal horizontal stress direction in the Transverse Ranges compared with central California implies that the plane of maximum right lateral shear stress is also rotated counterclockwise relative to that in central California. This supports the possibility that the “big bend” in the San Andreas fault may be a consequence of the negative buoyancy forces acting in the Transverse Ranges, and not the cause of Transverse Ranges formation, as has often been assumed.