Showing papers on "Stress field published in 1991"
TL;DR: In this paper, the inverse problem of 3D rotation of double-couple earthquake sources is solved in an analytical form, where each pair of focal mechanisms or seismic moment tensor solutions is found all four rotations which rotate one mechanism into another.
Abstract: SUMMARY
We discuss 3-D rotations by which one double-couple earthquake source can be rotated into another arbitrary double-couple. Due to the symmetry of double-couple sources, there are four such rotations. An algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3-D rotation of double-couple earthquake sources, i.e., for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another. This algorithm may be used in a wide variety of studies of stress field causing earthquakes, investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region, etc. The same inversion algorithm can be used to study the 3-D rotation of any symmetric second-rank tensor, such as the stress or strain tensor.
297 citations
TL;DR: In this paper, an asymptotic elasticity problem is analyzed to predict whether a straight crack path can occur within a brittle adhesive layer, and the location of the crack in terms of the combination of applied intensity factors and the mismatch in elastic moduli between the layer and the adjoining material.
242 citations
TL;DR: In this paper, a plane-strain finite-element analysis and a local stress-based criterion for cleavage fracture are combined to establish specimen size requirements (deformation limits) for testing in the transition region which assure a single parameter characterization of the crack-tip stress field.
Abstract: Single edge-notched bend (SENB) specimens containing shallow cracks (a/W < 0.2) are commonly employed for fracture testing of ferritic materials in the lower-transition region where extensive plasticity (but no significant ductile crack growth) precedes unstable fracture. Critical J-values Jc) for shallow crack specimens are significantly larger (factor of 2–3) than the Jc)-values for corresponding deep crack specimens at identical temperatures. The increase of fracture toughness arises from the loss of constraint that occurs when the gross plastic zones of bending impinge on the otherwise autonomous crack-tip plastic zones. Consequently, SENB specimens with small and large a/W ratios loaded to the same J-value have markedly different crack-tip stresses under large-scale plasticity. Detailed, plane-strain finite-element analyses and a local stress-based criterion for cleavage fracture are combined to establish specimen size requirements (deformation limits) for testing in the transition region which assure a single parameter characterization of the crack-tip stress field. Moreover, these analyses provide a framework to correlate Jc)-values with a/W ratio once the deformation limits are exceeded. The correlation procedure is shown to remove the geometry dependence of fracture toughness values for an A36 steel in the transition region across a/W ratios and to reduce the scatter of toughness values for nominally identical specimens.
209 citations
TL;DR: In this paper, a non-local statistical theory of size effect was proposed, which combines the size effect due to fracture energy release with the effect of random variability of strength having Weibull distribution.
Abstract: The failure probability of structures must be calculated from the stress field that exists just before failure, rather than the initial elastic field. Accordingly, fracture‐mechanics stress solutions are utilized to obtain the failure probabilities. This leads to an amalgamated theory that combines the size effect due to fracture energy release with the effect of random variability of strength having Weibull distribution. For the singular stress field of linear elastic fracture mechanics, the failure‐probability integral diverges. Convergent solution, however, can be obtained with the nonlocal‐continuum concept. This leads to nonlocal statistical theory of size effect. According to this theory, the asymptotic size‐effect law for very small structure sizes agrees with the classical‐power law based on Weibull theory. For very large structures, the asymptotic size‐effect law coincides with that of linear elastic fracture mechanics of bodies with similar cracks, and the failure probability is dominated by the...
160 citations
TL;DR: In this paper, the stiffness reduction as a result of multiple transverse cracking in cross-ply laminates and the crack density dependence on the applied tensile stress are analyzed by linear elastic fracture mechanics.
Abstract: The stiffness reduction as a result of multiple transverse cracking in cross-ply laminates and the crack density dependence on the applied tensile stress are analyzed by linear elastic fracture mechanics. The stress field distribution is obtained by the principle of minimum complementary energy. Two models are suggested which describe the non-uniform stress distribution in the thickness direction of the 0° layer. They contain the variational approach presented by Hashin as a particular case. Elastic ply properties and the Mode I critical strain energy release rate GIc for transverse cracking are the experimental data needed. Model predictions are compared with experimental data for glass fiber/epoxy, AS4/3502, and AS/3501-06 carbon fiber/epoxy cross-ply laminates. The predictions from the suggested models describe both the constraint effect and the crack saturation phenomenon.
143 citations
TL;DR: In this article, three methods are described: displacement extrapolation, the stiffness derivative and the area and volume J-integrals, and the virtual crack extension which is employed by the latter two methods.
Abstract: Use of the finite element method to treat two and three-dimensional linear elastic fracture mechanics problems is becoming common place. In general, the behavior of the displacement field in ordinary elements is at most quadratic or cubic, so that the stress field is at most linear or quadratic. On the other hand, the stresses in the neighborhood of a crack tip in a linear elastic material have been shown to be square root singular. Hence, the problem begins by properly modeling the stresses in the region adjacent to the crack tip with finite elements. To this end, quarter-point, singular, isoparametric elements may be employed; these will be discussed in detail. After that difficulty has been overcome, the stress intensity factor must be extracted from either the stress or displacement field or by an energy based method. Three methods are described here: displacement extrapolation, the stiffness derivative and the area and volume J-integrals. Special attention will be given to the virtual crack extension which is employed by the latter two methods. A methodology for calculating stress intensity factors in two and three-dimensional bodies will be recommended.
128 citations
TL;DR: In this article, a new inversion technique was developed that solves for a uniform stress field that is superimposed on a given spatially varying stress field, and a series of simulations were performed to test both the new method and an older method that uses only the uniform component of the stress field.
Abstract: The ML = 5.9 Whittier Narrows, California, earthquake of October 1, 1987, triggered a complex aftershock sequence. The aftershocks had many different focal mechanisms including thrusting on E-W striking, north dipping planes (similar to the main shock), right-lateral motion on NW-SE striking planes (similar to the ML = 5.3 aftershock on October 4, 1987), thrusting on N-S striking planes, and left-lateral motion on N-S striking planes. I attempt to interpret these mechanisms in terms of a stress field that may have caused them. Previously, stress inversion methods based on focal mechanisms assumed that the stress field was spatially uniform. In order to test for the spatially varying effect of the main shock's dislocation on the aftershocks' focal mechanisms a new inversion technique was developed that solves for a uniform stress field that is superimposed on a given spatially varying stress field. A series of simulations were performed to test both the new method and an older method that uses only the uniform component of the stress field. These simulations show that both techniques work but will be limited by the amount of noise in the data and the accuracy to which the given spatially varying stress field resembles the actual spatially varying stresses. Most importantly, the simulations show that the older methods do work when the stress field has a uniform component that is at least as large as the spatially varying component. The simulations also show that when applying the older stress inversion techniques, one can determine if the results are valid, and the amount of spatially varying stresses present, by examining the misfit between the data and the model. Application of these techniques to the Whittier Narrows aftershocks suggests that the uniform component of the stress field, and the complex faulting, corresponds to the response of an elastic halfspace to a simple regional N-S compression. The misfit between the data and the uniform model demonstrate the presence of spatially varying stresses at Whittier Narrows; however, their form, as shown by the simulations, can not be determined with this data set and these techniques.
128 citations
TL;DR: In this article, the direction of fracture initiation for in-plane shear load was found to be away from the line that bisects the notch, and the fracture angle decreases from ± 70.5° to ± 52.0° as the half notch angle is increased from 0° to 60°.
122 citations
TL;DR: In this article, various aspects of stress fields near an interface crack in three-dimensional bimaterial plates are investigated, and accurate prediction of the interface fracture behavior requires not only the G distribution but also the variations of phase angles along the crack front.
Abstract: Various aspects of stress fields near an interface crack in three-dimensional bimaterial plates are investigated. Due to the nature of the resulting deformation field, three-dimensional effects are more critical in a bimaterial plate than in a homogeneous plate. In the close vicinity of the crack front, the stress field is characterized by the asymptotic bimaterial K -field, and its domain size is a very small fraction of a plate thickness. Unlike a homogeneous case, the asymptotic field always consists all three modes of fracture, and an interface crack must propagate under mixed-mode conditions. Furthermore, computational results have shown that the two phase angles representing the relative magnitudes of the three modes strongly depend on the bimaterial properties. It has been also observed that a significant antiplane (Mode III) deformation exists along the crack front, especially near the free surface. Since experimental investigations have shown that critical energy release rate G c is highly dependent on the phase angles, accurate prediction of the interface fracture behavior requires not only the G distribution but also the variations of phase angles along the crack front.
121 citations
TL;DR: In this paper, Solfatara Creek, a 5.2m-wide, 0.7m-deep gravel bed channel where flow exits an upstream bend and shoals over a bar in a straight reach, is used to examine patterns of flow and the fluid forces determining the flow field.
Abstract: Alternate bars are important features in alluvial channels as they determine flow and transport patterns. They appear fundamental to selection of meander wavelengths and the geometry of bends. Bend flow has been studied extensively: far less study has been made of flow over alternate bars. Field results from Solfatara Creek, a 5.2-m-wide, 0.2–0.7-m-deep gravel bed channel where flow exits an upstream bend and shoals over a bar in a straight reach, are used to examine patterns of flow and the fluid forces determining the flow field. Large cross-sectional area changes, tied primarily to variation in depth, force large stream-wise accelerations and substantial cross-stream flow off the central bar. The topographically driven downstream and cross-stream accelerations are sufficiently large that their influence upon the balance of forces is of the same order as the pressure gradient and the boundary shear stress. The importance of convective accelerations in the downstream flow equation in this straight reach concurs with bend flow results, but the similar importance of convective accelerations in the cross-stream equation contrasts with results from bend flow. While part of the difference may be attributed to the lower stage conditions herein, in the absence of significant curvature change the cross-stream force balance depends upon the flow going over and around the bar. Local boundary shear stress estimated from the law-of-the-wall and a roughness algorithm decreases out of the upstream bend, increases over the bar top to values approaching the threshold for motion, and then decreases in deeper flow. Strong bed surface coarsening maintains the topography in a stress field that would otherwise lead to planation of the bar top and filling of the deeper regions.
119 citations
01 Nov 1991
TL;DR: In this article, a finite element procedure is presented for the analysis of the buckling and postbuckling behavior of cracks in plates loaded in tension, where the loading direction is perpendicular to the crack faces.
Abstract: A finite element procedure is presented for the analysis of the buckling and postbuckling behavior of cracks in plates loaded in tension. The procedure proposed is applied to the problem of the centrally cracked plate in tension where the loading direction is perpendicular to the crack faces. The results of the analysis show that the buckling deformations can cause a considerable amplification of the stress intensity around the crack tip. This effect, which is due to a redistribution of the stress field in the plate, increases with the length of the crack.
TL;DR: In this article, the authors carried out a systematic search for common features associated with intraplate earthquakes and found that intra-plate earthquakes occur by reactivation of pre-existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion.
TL;DR: In this article, a model for the Neogene tectonic evolution of the Pannonian area combines three contrasting mechanisms to explain this observation: 1) Appropriate rotation of the regional (e.g., European) stress field, 2) rotation of larger tectonics under a stable regional stress field; and 3) coherent rotation of smaller, detached continental blocks under a consistent regional stress fields.
TL;DR: In this paper, the authors show that the image force of an edge dislocation near a finite length crack depends on where the dislocation is originated, and that the dislocations will shield or antishield both crack tips if it is originated from elsewhere.
Abstract: The stress field of an edge dislocation near a finite length crack depends on where the dislocation is originated. If the dislocation is emitted from the crack which is originally stress-free, the image force increases with decreasing crack length. But the opposite is true if the dislocation is originated from elsewhere. At the same distance from the crack tip, the image force for the former is always larger than that for the latter. They become equal only if the crack is semi-infinitely long. If the dislocation is emitted from one of the crack tips, it generally will shield this crack tip but antishield the other tip. However the dislocation will shield or antishield both crack tips if it is originated from elsewhere.
TL;DR: In this paper, a fundamental description of slow crack growth in polyethylene is given in terms of tie molecules and the stress field on the boundary of the craze from which fracture initiates.
Abstract: Slow crack growth in a wide variety of polyethylenes have been investigated. The quantitative relationship between: (1) the external variables such as stress, temperature, stress intensity and J-integral; (2) the morphological variable such as density and crystal size and (3) molecular variables such as molecular weight, branch density and branch distribution and the rate and time to failure for slow crack growth will be presented. The kinetics of slow crack growth is correlated with the microstructural changes. A fundamental description of slow crack growth is given in terms of tie molecules and the stress field on the boundary of the craze from which fracture initiates.
TL;DR: Major advantages of the present system over those previously described in the literature are that sample mounting procedures are simplified, there is provision for independent adjustment of stress field uniformity and measurement of the applied point forces and faster strain rates can be imposed on the relatively small samples tested.
Abstract: A testing facility for measuring the biaxial mechanical properties of highly deformable membranes is described. Forces are applied, via strain-gauge force transducers, to four points on each side of an initially square 12 to 25 mm membrane sample to produce biaxial extensions of up to 80 percent of undeformed length. Strain is estimated from the displacement of markers bounding a 1 to 2 mm central square. The accuracy of stress and strain field measurements has been assessed by finite element analysis of a biaxially-loaded isotropic elastic membrane. Major advantages of the present system over those previously described in the literature are that 1) sample mounting procedures are simplified, 2) there is provision for independent adjustment of stress field uniformity and measurement of the applied point forces and 3) faster strain rates can be imposed on the relatively small samples tested.
TL;DR: In this paper, the authors considered the mode 3 crack problem for two bonded homogeneous half planes, where the interfacial zone was modelled by a nonhomogeneous strip in such a way that the shear modulus is a continuous function throughout the composite medium and has discontinuous derivatives along the boundaries.
Abstract: The mode 3 crack problem for two bonded homogeneous half planes was considered. The interfacial zone was modelled by a nonhomogeneous strip in such a way that the shear modulus is a continuous function throughout the composite medium and has discontinuous derivatives along the boundaries of the interfacial zone. The problem was formulated for cracks perpendicular to the nominal interface and was solved for various crack locations in and around the interfacial region. The asymptotic stress field near the tip of a crack terminating at an interface was examined and it was shown that, unlike the corresponding stress field in piecewise homogeneous materials, in this case the stresses have the standard square root singularity and their angular variation was identical to that of a crack in a homogeneous medium. With application to the subcritical crack growth process in mind, the results given include mostly the stress intensity factors for some typical crack geometries and various material combinations.
TL;DR: In this paper, a Multigrid extension of a stationary solver is outlined for the EHL solution of a line contact under transient conditions, which is applied to calculate pressure and film thickness profiles at each time step.
Abstract: In this paper a Multigrid extension of a stationary solver is outlined for the EHL solution of a line contact under transient conditions. The solver is applied to calculate pressure and film thickness profiles at each time step when an indentation is moving through the contact, which results in an asymmetric pressure profile. The time-dependent results are compared with the stationary solutions. The pressure as a function of time is presented as well as the integrated pressure (over time) as a function of the spatial coordinate. These time-dependent pressures are used to compute the sub-surface stress field, which shows higher stresses below the trailing edge of the indentation. Therefore the risk of fatigue is higher below the trailing edge of the indentation, as is experimentally observed. The transient pressures can be used for a fundamental study of the emitted frequency spectrum of rolling bearings, as used in condition monitoring.
TL;DR: In this article, the authors used edge-cracked bend bar specimens loaded in anti-symmetric and symmetric four-point bend configurations to investigate fracture micro-mechanisms of four grades of steel.
TL;DR: In this paper, the authors used polarity and amplitude data to detect posteruption earthquakes in the country rock surrounding a cylindrical magma body located within the aseismic volume.
Abstract: Earthquakes following the May 18, 1980, and June 12, 1980, explosive eruptions of Mount St. Helens were concentrated at depths below 6 km. The hypocenters of these posteruption earthquakes define two seismic lobes separated by an aseismic volume of 2 km width that is located beneath the position of the crater. The timing and location of the posteruption seismicity suggests that the earthquakes occurred in the country rock surrounding a magma body located within the aseismic volume. The withdrawal of magma caused a pressure decrease within the reservoir, and the earthquakes occurred as a brittle response to the resulting stress change. Focal mechanism solutions for posteruption earthquakes distributed within the seismic lobes are calculated using polarity and amplitude data. Results show that a perturbation from the regional stress field occurs between depths of 7 and 11 km. This anomalous stress field is successfully modeled by a decrease in pressure within a cylindrical magma body located between the seismic lobes and subject to conditions representing the regional shear stress regime. In the best fitting model the magma body is centered at 46.204°N, 122.187°W, 600 m to the north of the present dome, and is under a regional shear stress of 20 bars. The radius of the chamber is calculated to be between 0.65 and 0.75 km when using pressure drops within the cylinder of 220 and 150 bars respectively. The magma body extends from 7 to 11 km and has a volume of between 5 and 7 km3 Posteruption earthquakes located below 11 km fall on a northeast striking fault that is preferentially aligned with the regional tectonic stress regime. This fault may be a conduit to transport magma to the shallow reservoir from greater depths within the crust.
TL;DR: In this paper, the influence of the stress field and the material parameters on the development of Riedel shears was investigated by applying a numerical model to evaluate the effect of these parameters.
TL;DR: The main results from the Fennoscandian Rock Stress Data Base (FRSDB) are presented in this article, where it is suggested that ridge push from the Mid-Atlantic Ridge is the major stress-generating mechanism.
TL;DR: In this paper, analytical solutions for displacement and stress fields of in-plane deformation of two anisotropic half-planes, forming a composite bimaterial, with an interface crack, assuming strictly two-dimensional problems are given.
Abstract: Based on linear elastic fracture mechanics, analytic solutions are given for displacement and stress fields of in-plane deformation of two anisotropic half-planes, forming a composite bimaterial, with an interface crack, assuming strictly two-dimensional problems; this requires suitable orientation of the material symmetry axes to ensure decoupling of the anti-plane fracture mode from the in-plane ones. It is shown that the field equations are fully characterized in terms of four dimensionless parameters, and these parameters are expressed in terms of the twelve involved elastic constants, six for each half-plane. Analytic solutions are given for two models: (1) the fully open-crack model, involving oscillatory square-root singularities at crack tips ; and (2) the Comninou model which allows possible small contact zones close to the crack tips. Analytic expressions are obtained for the crack opening displacement, the size of the contact zone, the total force transmitted across the contact zone, and the stress field. The results are discussed and related to those for isotropic bimaterials, given by Gautesen and Dundurs.
TL;DR: In this paper, a classification of dilational fracture geometry is proposed, which applies to structures that can be characterized by the combination of a fracture system and a dilation vector field.
Abstract: A classification of dilational fracture geometry is proposed. It applies to structures that can be characterized by the combination of a fracture system and a dilation vector field. The classification is illustrated with examples of igneous dykes, pegmatites, and pseudotachylites. Segmentation in the form of offsets, jogs, or bifurcations is common to most fracture systems. Four basic types of dilational fracture systems are distinguished on the basis of the geometry of segmentation. These are: irregular, braided, en-echelon, and zigzag. Zigzag fracture systems are further differentiated. They consist of newly formed, obliquely dilated fractures or, alternatively, of pre-existing planes in the host-rock that are reactivated by oblique dilation. This paper is the first to actually report an igneous zigzag-dyke involving newly formed fractures. Rotation of the regional stress field in the direction of propagation leads to en-echelon segmentation. Braided fracture systems reflect high local stress-intensities, probably related to propagation rate. Two possibilities exist for the formation of zigzag dykes consisting of newly formed fractures that are obliquely dilated. They may form by extreme interaction of tensile fracture segments in a regional stress field with a low differential stress. Alternatively, they may form in a regional stress field with high differential stress through the propagation of shear fractures. Segmentation of dykes, characterized by offsets, is common. Such segmentation can be the result of protrusions of the fracture termination. Offsets also occur where a dyke cuts an older planar structure. Such offsets are the result of the local inhibition of fracture propagation. The resulting apparent offset can lead to a misinterpretation of relative age. Apophyses form as a result of the dilation of a segmented fracture system.
TL;DR: In this article, the relationship between dynamics and stress field of the oceanic lithosphere is investigated and the ridge-push force is modelled as a pressure gradient integrated over all contributing parts of the lithosphere, while the slab-pull force is dependent on the age of the subducting lithosphere.
Abstract: We outline the methodology of our numerical studies aimed at increasing the understanding of the relation between dynamics and stress field of the lithosphere with particular reference to oceanic lithosphere. The ridge-push force is modelled as a pressure gradient integrated over all contributing parts of the lithosphere. The slab-pull force is modelled as being dependent on the age of the subducting lithosphere. We parametrize the resistive forces and determine the unknown parameters by requiring the total torque of all forces acting on the plate to vanish. We illustrate the approach by the presentation and discussion of new modelling results for the Pacific plate.
TL;DR: In this paper, the equilibrium shape of a martensite plate can be calculated by treating the interface as a distributed array of dislocations and by calculating their equilibrium distribution, and it is shown that the shape of an isolated twin is an ellipse to first approximation.
Abstract: It is shown that the equilibrium shape of a twin or martensite plate can be calculated by treating the interface as a distributed array of dislocations and by calculating their equilibrium distribution. The shape of an isolated twin is an ellipse to first approximation. Second approximation treatments show that the tip of the twin sharpens with increasing stress for the screw dislocation case while it becomes blunter with increasing stress for the edge dislocation case. A colony of twins is treated in much the same way as a stacked array of piled-up dislocations for the screw dislocation case. It is found that the twins flatten out with decreasing separation. Expressions are derived for the stress-field and for the strain energy of such stacked twins. It is shown that the twin spacing should be proportional to the square root of the twin length, from which the twin boundary energy can be calculated.
TL;DR: In this paper, the 3-D stress field of a cylindrical fiber embedded into a resin matrix is analyzed and a debonding initiation at the fiber/matrix interface is predicted.
Abstract: This paper deals with the 3-D stress field of a cylindrical fiber which is embedded into a resin matrix. The composite is then subjected to a uniform tensile load so. The strain energy release rate is computed and the criterion is used to predict debonding initiation at the fiber/matrix interface. The analysis shows that this failure is most likely to occur at the free surface, i.e. the region where the fiber intersects a free surface, for example a hole, an edge, or a crack. Moreover, it will occur at approximately (1/10) the load value required for the same failure to commence at the center of the fiber length.The results are also extended to include a doubly periodic array of fibers which are embedded into a matrix. Based on 3-D considerations, the stiffness matrix is shown to increase as the volume fraction of the fibers increases. Similarly, the stress sr, in the matrix is shown to decrease as the volume fraction of the fibers increases.
TL;DR: The Ebro basin joints strike uniformly NNW-SSE throughout an area of at least 10000 km2 and they are parallel or subparallel to the direction of greatest horizontal stress extrapolated from in situ stress measurements and fault-plane solutions of earthquakes as discussed by the authors.
Abstract: A neotectonic joint is a crack which propagated in a tectonic stress field that has persisted with little or no change of orientation until the present day. Investigating neotectonic joints is of value because the approximate orientation of the contemporary stress field can be inferred from them. Although exposed neotectonic joints in the flat-lying sedimentary rocks of some cratons are related to regional stress fields, their initiation and propagation occurred close to the Earth's surface. For example, neotectonic joints in the centre of the Ebro basin (N. Spain) preferentially developed in a thin, near-surface channel sited within a sequence of weak Miocene limestones underlying the upper levels of plateaux. The Ebro basin joints strike uniformly NNW-SSE throughout an area of at least 10000 km2 and they are parallel or subparallel to the direction of greatest horizontal stress extrapolated from in situ stress measurements and fault-plane solutions of earthquakes. 1. Preamble This paper has three aims. Firstly, to review the general attributes of exposed neotectonic joints, secondly, to demonstrate that in S. England/N. France and the Ebro basin (Spain) the directions of greatest horizontal principal stress that were inferred from neotectonic joints are parallel to those determined later from geophysical observations, and thirdly, to discuss why neotectonic joints in the Ebro basin are better developed in weak limestones cropping out in the upper parts of plateaux. In this paper the word neotectonic is used to indicate that a fracture was propagated in a tectonic stress field that has persisted with little or no change of orientation until the present day (Hancock & Engelder 1989). A fracture is called a joint if, at the scale of observation possible in the field, it is barren and there is no measurable offset related to shear, dilation or pressure solution. Because joints are the most abundant of non-penetrative geological structures they are of great potential value for tracking the orientations of principal stress axes at the time of failure. Confidence in the value of joints as stress indicators is greatest where they are uniformly arranged throughout a large area of flat-lying rocks.
15 Oct 1991
TL;DR: In this article, the stresses associated with large-scale tectonic deformation have three possible origins: (1) plate-boundary forces counterbalanced by viscous drag beneath the plates; (2) density heterogeneities situated within the plates (say at depths shallower than 200 km); and (3) mass heterogeneity in the deep mantle.
Abstract: The stresses associated with large-scale tectonic deformation have three possible origins: (1) plate-boundary forces counterbalanced by viscous drag beneath the plates; (2) density heterogeneities situated within the plates (say at depths shallower than 200 km); (3) mass heterogeneities in the deep mantle. The first two are shown to be equally important for the understanding of the stress field. No topography (no vertical stress) seems to be associated with lower-mantle mass anomalies. This is most compatible with a two-layer convective mantle where the lower-mantle mass anomalies, mechanically decoupled from the lithosphere, are unable to induce tectonic stresses.
TL;DR: The World Stress Map Project (WSMP) as mentioned in this paper is a global cooperative effort to compile and interpret data on the orientation and relative magnitudes of the contemporary in situ tectonic stress field in the Earth's lithosphere.
Abstract: The World Stress Map Project is a global cooperative effort to compile and interpret data on the orientation and relative magnitudes of the contemporary in situ tectonic stress field in the Earth's lithosphere. Horizontal stress orientations show regionally uniform patterns throughout many continental intraplate regions. These regional intraplate stress fields are consistent over regions 1000-5000 km wide or ca. 100 times the thickness of the upper brittle part of the lithosphere (ca. 20 km) and about 10-15 times the thickness of typical continental lithosphere (ca. 150-200 km). Relative stress magnitudes or stress regimes in the lithosphere are inferred from direct in situ stress measurements and from the style of active faulting. The intraplate stress field in both the oceans and continents is largely compressional with one or both of the horizontal stresses greater than the vertical stress. The regionally uniform horizontal intraplate stress orientations are generally consistent with either relative or absolute plate motions indicating that plate-boundary forces dominate the stress distribution within the plates. Since most regions of normal faulting occur in areas of high elevation, the extensional stress regimes in these areas can be attributed to superimposed bouyancy forces related to crustal thickening and/or lithosphere thinning; stresses derived from these bouyancy forces locally exceed midplate compressional stresses. Evaluating the effect of viscous drag forces acting on the plates is difficult. Simple driving or resisting drag models (with shear tractions acting parallel or antiparallel to plate motion) are consistent with stress orientation data; however, the large lateral stress gradients across broad plates required to balance these tractions are not observed in the relative stress magnitude data. Current models of stresses due to whole mantle flow inferred from seismic tomography models (and with the inclusion of the effect of high density slabs) predict a general compressional stress state within continents but do not match the broad-scale horizontal stress orientations. The broad regionally uniform intraplate stress orientations are best correlated with compressional plate-boundary forces and the geometry of the plate boundaries.