Observed Stress Pattern Research Articles

Modeling irradiation-induced intragranular gas bubble in tungsten under external tensile loading

Microstructure damage created by high-energy particle irradiation has an inevitable effect on the performance of material. Helium (He) as the transmutation element in irradiated solid prefers to occupy the vacancy (V) center to form HeV complex, which in turn induces the formation of He bubble. Herein, the external applied stress driven irradiation-induced He bubble formation and evolution in single-crystalline tungsten (W) has been investigated using the phase-field method. Importantly, the trapping and resolution kinetic behavior between He atom and He bubble is described by the diffusion coefficient in terms of rate theory continuum model, and the effect of external stress on the movements of vacancy, self-interstitial and He atom has been implemented into their diffusivities as well. We first concentrate on the intrinsic lattice distortion (stress) patterns of void and bubble to validate the developed model by comparing the reported numerical results. Then, the accelerated growth velocity of bubble along the loading direction is predicted, which agrees well with the previously observed stress pattern around the void/bubble. The evolution behaviors of the stress-assisted single, bi-dispersed and multiple bubbles vary with the direction and magnitude of external loading, indicating a strong correlation between the size and density of bubble and the loading level. It is found that with the contribution of increasing external stress, more bubbles can be generated at the formation stage and visible bubbles tend to reduce at the coarsening stage due to bubble coalescence.

Role of double-subduction dynamics in the topographic evolution of the Sunda Plate

SUMMARY The Sunda Plate has shaped itself in a complex tectonic framework, driven by the interactions of multiple subduction zones in its history. Using thermomechanical computational fluid dynamic models we show in this paper how the in-dip double-subduction dynamics has controlled the first-order 3-D topography of this plate, currently bounded by two major N–S trending active trenches: Andaman–Sumatra–Java and Philippines on its western and eastern margins, respectively. We consider six E–W transects to account for an along-trench variation of the subduction parameters: subduction rate (Vc), shallow-depth (200–300 km) slab dip (α) and intertrench distance (ITD, λ) in our 2-D numerical experiments. The deviatoric stress fields and the topographic patterns are found to strongly depend on λ. For large ITDs (λ = 2000–3000 km), the overriding plate develops dominantly tensile stresses in its central zone, forming low topographic elevations. Decreasing λ results in a transition from extensional to contractional deformation, and promotes topographic uplift in the southern part. We explain these effects of λ in terms of the sublithospheric flow vortex patterns produced by the subducting slabs. Large λ (> 2000 km) generates non-interacting flow vortices, located close to the two trenches, leaving the mantle region beneath the overriding plate weakly perturbed. In contrast, small λ results in their strong interaction to produce a single upwelling zone, which facilitates the overriding plate to gain a higher topographic elevation. The stress field predicted from our model is validated with the observed stress patterns. We also interpolate a 3-D topographic surface and vertical uplift rates from the serial model sections, and compare them with the observed surface topography of the Sunda Plate.

Stress responses in high-fidelity simulation among anesthesiology students

Simulation sessions can produce high-fidelity emergency situations that facilitate the learning process. These sessions may also generate a complex stress response in the learners. This prospective observational study assessed psychological, physiological, immunological, and humoral levels of stress during high-fidelity simulation training. Fifty-six undergraduate medicine students who took part in a medical simulation session were assigned team roles (physician, nurse or assistant). Subsequently, each participant was assessed before the scenario (T0), after the procedure (T1), and two hours later (T2). Psychological stress and anxiety were measured at T0 and T1, using the State-Trait Anxiety Inventory (STAI) and Dundee Stress State Questionnaire (DSSQ). Cortisol, testosterone, secretory immunoglobulin class A (sIgA), alpha-amylase, and oxygen saturation level were measured at T0, T1, and T2, as was the physiological response indicated by heart rate (HR) and blood pressure (BP). It was found that the onset of task performance was related to increased anticipatory worry and higher oxygen saturation. The participants reported decreased worry, followed by increased emotional distress after the simulation training (T1). Participants trait anxiety predicted the intensity of worry, distress and task engagement. In contrast, no clear relationships were found between trait anxiety and biological stress markers. Testosterone levels were growing significantly in each phase of measurement, while physiological responses (BP, HR) increased at T1 and declined at T2. The levels of stress markers varied depending on the assigned roles; however, the trajectories of responses were similar among all team members. No evidence for prolonged cortisol response (T1, T2) was found based on psychological stress at the onset of simulation (T0). Regression analysis followed by receiver operating characteristics analyses showed uncertain evidence that initial state anxiety and worry predicted the levels of sIgA. Medical students are relatively resilient in terms of stress responses to medical simulation. The observed stress patterns and interrelationships between its psychological, physiological, hormonal, and immunological markers are discussed in accordance with theoretical concepts, previous research work, and further recommendations.

Mapping leaf chlorophyll content from Sentinel-2 and RapidEye data in spruce stands using the invertible forest reflectance model

Leaf chlorophyll plays an essential role in controlling photosynthesis, physiological activities and forest health. In this study, the performance of Sentinel-2 and RapidEye satellite data and the Invertible Forest Reflectance Model (INFORM) radiative transfer model (RTM) for retrieving and mapping of leaf chlorophyll content in the Norway spruce (Picea abies) stands of a temperate forest was evaluated. Biochemical properties of leaf samples as well as stand structural characteristics were collected in two subsequent field campaigns during July 2015 and 2016 in the Bavarian Forest National Park (BFNP), Germany, parallel with the timing of the RapidEye and Sentinel-2 images. Leaf chlorophyll was measured both destructively and nondestructively using wet chemical spectrophotometry analysis and a hand-held chlorophyll content meter. The INFORM was utilised in the forward mode to generate two lookup tables (LUTs) in the spectral band settings of RapidEye and Sentinel-2 data using information obtained from the field campaigns. Before generating the LUTs, the sensitivity of the model input parameters to the spectral data from RapidEye and Sentinel-2 were examined. The canopy reflectance of the studied plots were obtained from the satellite images and used as input for the inversion of LUTs. The coefficient of determination (R2), root mean square errors (RMSE), and the normalised root mean square errors (NRMSE), between the retrieved and measured leaf chlorophyll, were then used to examine the attained results from RapidEye and Sentinel-2 data, respectively. The use of multiple solutions and spectral subsets for the inversion process were further investigated to enhance the retrieval accuracy of foliar chlorophyll. The result of the sensitivity analysis demonstrated that the simulated canopy reflectance of Sentinel-2 is sensitive to the alternation of all INFORM input parameters, while the simulated canopy reflectance from RapidEye did not show sensitivity to leaf water content variations. In general, there was agreement between the simulated and measured reflectance spectra from RapidEye and Sentinel-2, particularly in the visible and red-edge regions. However, examining the average absolute error from the simulated and measured reflectance revealed a large discrepancy in spectral bands around the near-infrared shoulder. The relationship between retrieved and measured leaf chlorophyll content from the Sentinel-2 data had a higher coefficient of determination with a higher NRMSE (NRMSE = 0.36 μg/cm2, R2 = 0.45) compared to those obtained using the RapidEye data (NRMSE = 0.31 μg/cm2 and R2 = 0.39). Using the mean of the ten best solutions (retrieved chlorophyll) the retrieval error for both Sentinel-2 and RapidEye data decreased (NRMSE = 0.34, NRMSE = 0.26, respectively), as compared to only selecting the single best solution. When the Sentinel-2 red edge bands were used as the spectral subset, the retrieval error of leaf chlorophyll decreased indicating the importance of red edge, as well as properly located spectral bands, for leaf chlorophyll estimation. The chlorophyll maps produced by the inversion of the two LUTs effectively represented the variation of foliar chlorophyll in BFNP and confirmed our earlier findings on the observed stress pattern caused by insect infestation. Our findings emphasise the importance of multispectral satellites which benefits from red edge spectral bands such as Sentinel-2 as well as RapidEye for regional mapping of vegetation foliar properties, particularly, chlorophyll using RTMs such as INFORM.

Residual Stress in Selective Laser Melted Inconel 718: Influence of the Removal from Base Plate and Deposition Hatch Length

Abstract The residual stress distribution in IN718 elongated prisms produced by selective laser melting was studied by means of neutron (bulk) and laboratory X-ray (surface) diffraction. Two deposition hatch lengths were considered. A horizontal plane near the top surface (perpendicular to the building direction) and a vertical plane near the lateral surface (parallel to the building direction) were investigated. Samples both in as-built (AB) condition and removed from the base plate (RE) were characterized. While surface stress fields seem constant for the AB condition, X-ray diffraction shows stress gradients along the hatch direction in the RE condition. The stress profiles correlate with the distortion maps obtained by tactile probe measurements. Neutron diffraction shows bulk stress gradients for all principal components along the main sample directions. We correlate the observed stress patterns with the hatch length, i.e., with its effect on temperature gradients and heat flow. The bulk stress gradients partially disappear after removal from the base plate.

Intraplate stress field in South America from earthquake focal mechanisms

We present an updated compilation of earthquake focal mechanisms in Brazil together with focal mechanisms from the sub-Andean region (mainly from global CMT catalogs). All earthquakes in the sub-Andean region show reverse (majority) or strike-slip faulting mechanisms. Focal mechanisms in Brazil show reverse, strike-slip and normal faulting. Focal mechanisms of nearby earthquakes in the same tectonic environment were grouped and inverted for the stress tensor. In the sub-Andean region, stresses are compressional, as expected, with the principal major compression (S1) roughly E-W, on average. A slight rotation of S1 can be observed and is controlled by the orientation of the Andean plateau. In the sub-Andean region, the intermediate principal stress (S2) is also compressional (i.e., larger than the lithostatic pressure, Sv), a feature that is not always reproduced in numerical models published in the literature. In mid-plate South America stresses seem to vary in nature and orientation. In SE Brazil and the Chaco-Pantanal basins, S1 tends to be oriented roughly E-W with S2 approximately equal to S3. This stress pattern changes to purely compressional (both SHmax and Shmin larger than Sv) in the São Francisco craton. A rotation of SHmax from E-W to SE-NW is suggested towards the Amazon region. Along the Atlantic margin, the regional stresses are very much affected by coastal effects (due to continent/ocean spreading stresses as well as flexural effects from sediment load at the continental margin). This coastal effect tends to make SHmax parallel to the coastline and Shmin (usually S3) perpendicular to the coastline. Few breakout data and in-situ measurements are available in Brazil and are generally consistent with the pattern derived from the earthquake focal mechanisms. Although numerical models of global lithospheric stresses tend to reproduce the main large-scale features in most mid-plate areas, the S1 rotation from ∼E-W in SE Brazil to SE-NW in the Amazon region are not well explained by the current numerical models. This means that the observed stress pattern in mid-plate South America should provide new insights into upper mantle dynamics, distinct from current global convection models.

Unusual stress rotations within the Philippines possibly caused by slip heterogeneity along the Philippine fault

AbstractTo understand the complex tectonic interactions between subduction margins and transcurrent faults, we investigated the spatial distribution of stress orientations in the Philippines by using focal mechanisms derived from the waveform data of regional broadband seismic stations and Global Centroid Moment Tensor solutions. We investigated the spatial distribution of stress orientations by dividing the region into a central region containing the Philippine fault (PF) and regions to the east and west of the PF. Our stress tensor inversion results show that the σ1 axes in the central and eastern regions are WNW‐ESE oriented and parallel to the relative plate motion orientations. However, in the western region, the orientations of σ1 axes were different. In particular, the orientations of the σ1 axes in the southern part (Bohol region) differ substantially (differences exceed approximately 60°) from those of the relative plate motion. Furthermore, the orientations of the σ1 axes in the northern part (Mindoro and southwestern Luzon regions) differ by approximately 30° from those found throughout the Philippines. The σ1 axes in the Bohol region and the σ3 axes in the Mindoro and southwestern Luzon regions are parallel to the strike of the PF. It was demonstrated that our numerical model incorporating slip on the PF and interplate coupling is able to successfully reproduce the features of the observed stress pattern.

A revised crustal stress orientation database for Canada

The Canadian database on contemporary crustal stress has not been revised systematically in the past two decades. Here we present the results of our new compilation that contains 514 new data records for the orientation data of maximum compressive horizontal stress and 188 data records that were re-assessed. In total the Canadian stress database has now 1667 data records, which is an increase of about 45%. From these data, a new Canadian Stress map as well as one for the Province of Alberta is presented.To analyse the stress pattern, we use the quasi median on the circle as a smoothing algorithm that generates a smoothed stress map of the maximum compressive horizontal stress orientation on a regular grid. The newly introduced quasi interquartile range on the circle estimates the spreading of the data and is used as a measure for the wave-length of the stress pattern. The result of the hybrid wavelength analysis confirms that long spatial wavelength stress patterns (≥1000km) exist in large areas in Canada. The observed stress pattern is transmitted through the intra-plate regions.The results reveal that shorter spatial wave length variation of the maximum compressive horizontal stress orientation of less than 200km, prevails particularly in south-eastern and western Canada. Regional stress sources such as density contrasts, active fault systems, crustal structures, etc. might have a significant impact in these regions. In contrast to these variations, the observed stress pattern in the Alberta Basin is very homogeneous and mainly controlled by plate boundary forces and body forces. The influence of curvature of the Rocky Mountains salient in southern Alberta is minimal. The present-day horizontal stress orientations determined herein have important implications for the production of hydrocarbons and geothermal energy in the Alberta Basin.

Stress state along the Anninghe-Zemuhe fault zone, southwestern China, estimated from an array of stress orientation measurements with a new method

Measurements of in-situ stress orientations at relatively shallow depths were conducted at 11 sites along the Anninghe-Zemuhe fault zone, southwestern China, with a newly developed method. The Anninghe fault in the fault zone has been considered to have a potential for a large earthquake with a magnitude of about 7.5, while the Zemuhe fault shows very little such potential. The present study has mainly two objectives: one is to show new data of the spatial distribution of the stress orientations around the fault zone, which is obtained directly from the measurements; the other is to examine the possibility to detect a stress pattern in relation to the past activities of earthquakes along the fault zone. The observed principal stress orientations are distributed between the NNW-SSE and NW-SE directions, which is consistent with the earthquake focal mechanism solutions near the fault zone. On the other hand, it is unclear whether the observed stress pattern is related to past activities of the fault zone, since the data fluctuation was too large to determine this. We note that the stress orientations are favorable for slip on the Anninghe fault, while being unfavorable on the Zemuhe fault, from the present experimental data.

Seismicity, active faults, stress patterns, and rupture processes in the Hualien region, Taiwan, investigated using the 1990 Hualien earthquake sequence

The Hualien mainshock–aftershock sequence from December 1990 to January 1991 was used to investigate seismicity, active faults, stress patterns, and complex rupture processes in the Hualien region of eastern Taiwan. A combined data set, compiled from observations by the regional seismic network (Taiwan Telemetered Seismograph Network, TTSN) and a dense aftershock monitoring array (Hualien Temporary Seismic Network, HTSN), provided high-quality seismic data. Using these data, earthquake source parameters could be well constrained by the joint hypocenter determination (JHD) and double-difference relocation methods. These two relocation methods presented similar results and produced improved estimations of earthquake location. Station corrections determined by JHD showed significant lateral velocity variations across the Yuehmei fault. The relocated seismicity indicated that a previously known active fault, the Chimei fault, extends to offshore. Earthquake relocations also revealed a northwest dipping seismicity probably related to the Chimei fault. In addition, three sets of focal mechanism solutions are presented and their discrepancies are attributed to the complex rupture process. At first, earthquakes were initiated by thrust motions. Later, the rupture pattern changed to strike–slip motions. Variations in slip may reflect the fault geometry or rupture boundary conditions in the region. The observed stress patterns are considered to relate not only to the regional collision and mountain-building processes, but also to active faults in local structures.

Prefixation and stress in Old English In memoriam Richard Hogg (1944–2007)

Some questions not usually answered in the Old English (OE) philological and linguistic canon are: to what extent is the prosodic behavior of OE prefixes attributable to their lexical form vs. the morphosyntactic nature of the bases they attach to, what taxonomy covers the distribution of stressed and unstressed forms best, how do OE prefixes compare to Present Day English (PDE) prefixes, and what do stacked prefixes reveal about the morphology-prosody interface. The paper reexamines these questions, expands considerably the empirical data-base for their discussion, and offers an account of the observed stress patterns in terms of Optimality Theory (OT).

Orientation and nature of active crustal stresses determined by electromagnetic measurements in the Patagonian segment of the South America Plate

Based on electromagnetic measurements we determined the current stress directions in the uppermost continental crust of Patagonia between the active plate margin of the Chilean Pacific coast and the Argentinean passive Atlantic margin. Regional variations of the observed stress pattern are giving details onto the acting tectonic processes. We distinguish five regional stress domains with different prevailing horizontal stress directions (SH): 1. Southern Coastal Cordillera and Longitudinal Valley (SH = SSW–NNE), 2. Chiloe Island (SH = SW–NE), 3. Northern Patagonian Andes (SH = WSW–ENE), 4. Argentinean Pampa and Atlantic margin (SH = WNW–ESE) and 5. Southern Patagonian Andes (SH = WNW–ESE). These stress regimes can be related to the geometry of the subducting Nazca- and Antarctic plates, to the transform fault between the South America and Scotia plates and to passive margin processes along the Atlantic coast. Absolute plate motion and rapid relative plate convergence control the subduction geometry and therefore the stress directions along the convergent margin of the South America Plate and the structural style within and landward of the Magmatic Arc. The knowledge of current local stress directions permits the characterisation of potential fault kinematics. By in situ measuring of electromagnetic emissions from rocks we determined the maximum horizontal stress orientation in the uppermost crust using a new geophysical tool. Our investigations on the orientation of the stress regimes also allow conclusions about the causative forces of either tectonic or gravitational origin in this part of the South-America Plate.

The Matching of Experimental Polymer Processing Flows to Viscoelastic Numerical Simulation

Abstract This paper describes work carried out in order to match experimental processing flows to numerical simulation. The work has brought together a consortium that has developed reliable experimental methods by which processing flows can be achieved in the laboratory and then ranked against numerical simulation. A full rheological characterisation of a selected range of polymers was made and the results compared from different laboratories. The data was fitted to a number of rheological models. Multi-mode parameter fitting was universal for the linear viscoelastic response. Particular attention was paid to the non linear response of the material. Prototype industrial flow experiments were carried out for a number of geometries in different laboratories and the flow birefringence technique was used to map out the experimentally observed stress fields for different polymers in a range of complex flows that contained both extensional and shear flow components. Numerical simulation was carried out using a number of algorithms and a range of constitutive equations. In order to make a quantitative comparison between experiment and simulation, an Advanced Rheological Tool (ART) module was developed that was able in some cases to quantify the level of fit between the numerically predicted and the experimentally observed stress patterns. In addition the ART module was able to optimise certain non-linear parameters in order to improve the quality of fit between experiment and simulation.

Recent tectonic stress and crustal deformation in and around the Pannonian Basin: data and models

Abstract Recent (active) tectonics of the Pannonian Basin and its surroundings has been investigated using data from over 900 earthquake focal mechanism solutions, 200 borehole breakout analyses, some in-situ stress measurements and by applying finite element modelling technique. We have established a database for indicators of recent stress, and analysed the stress state of the region by the methods of the World Stress Map project. The alignments of the largest horizontal stresses have been mapped and the tectonic regimes were also determined. We present a map of seismoactive faults and seismic energy release combining historical and modern seismicity data and results of local seismotectonic studies. The pattern of earthquake slip vectors and the style of faulting are summarised in order to characterise the active deformations. Our results show that the alignment of the largest horizontal stress exhibits a radial pattern around the Adriatic sea. In the Southern Alps and northwestern Dinarides the largest horizontal stress (SH) is aligned N-S and thrust faulting is dominant. Along the southern Dinarides and the Dalmatian coast thrusting with strike-slip component can be observed. Here the trajectories of SH are aligned NE-SW. E-W aligned SH trajectories and normal faulting are characteristic of the Rhodope Massif. Thrust faulting of the Vrancea region seems to be distinct from the compressive regime around the Adriatic sea. In the Pannonian Basin borehole breakout analyses show that the direction of largest horizontal stress is changing from N-S in the western part to NE-SW in the east. Most of focal mechanisms and available hydraulic fracturing measurements indicate strike-slip and thrust faulting inside the basin. The lack of normal faulting mechanisms indicates that the extension of the basin has been terminated and a new compressive stress regime prevails. The crustal deformation of the area is controlled by the counterclockwise rotation of Adria with respect to Europe around a pole at the 45°N latitude and 6–10°E longitudes, which is inferred from satellite geodesy and supported by earthquake slip vectors. This movement can explain the shortening of the Southern Alps, and squeezing eastward the region between the Adriatic sea and the Mur-Murz line. Rotation of Adria generates thrusts along the Dalmatian coast, and this compressive deformation extends into the land far from the coastline, and leads to squeezing of the Pannonian Basin from the southwest. The seismicity pattern in the Pannonian Basin shows that earthquakes are restricted to the crust and the control by pre-existing (mostly Miocene) fault zones is strongly masked by random activity due to general weakness of the lithosphere. Although earthquakes are of small to medium magnitude (M ≤ 6), the cummulative energy release is remarkably higher than in the surrounding Carpathian arc. The Vrancea zone is the only exception, where high energy release in the crust and down to 200 km depth is associated with a relict subducted slab. Finite element stress modelling has been performed in order to simulate the observed stress pattern and, hence, to understand the importance of different possible stress sources in and around the Pannonian Basin. The observed radial stress pattern of the region can be well explained by the counterclockwise rotation of the Adriatic microplate as a first-order stress source. Additional boundary conditions, such as the active deformation at the Vrancea zone and the role of rigid crustal blocks at the Bohemian Massif and the Moesian Platform, can significantly effect the style of deformation and the alignment of the largest horizontal stress. Furthermore, our calculations show that differences in the crustal thickness and the presence of large scale fault zones in the Pannonian region have only local influence on the model results.

Sources of recent tectonic stress in the Pannonian region:inferences from finite element modelling

We present the results of finite element modelling of the recent stress field in the Pannonian basin and surrounding Alpine orogenic belt. Our results show that the recent, predominantly compressive, stress regime in the Alpine–Pannonian–Carpathian–Dinaric system is governed by distinct tectonic factors. Of great importance is the deformation of crustal blocks with different geometries and rigidities in an overall convergent setting associated with the Africa–Europe collision. The most important stress source appears to be the counterclockwise rotation of the Adriatic microplate at the southwest boundary of the Pannonian basin. This plate tectonic unit has been interpreted as moving independently of both the European plate and the African plate. Additional boundary conditions—active shortening and compression in the Vrancea zone and the Bohemian Massif, and the effect of the immobile Moesian Platform—also significantly influence the modelling results. The incorporation of additional stress sources such as crustal thickness variation and the presence of two main fault zones separating the primary tectonic units in the study area have only locally important effects but improve the fit between the calculated results and the observed stress pattern.

Observation of dislocation stresses in InP using polarization-resolved photoluminescence

Localized stresses have been observed on the surface of InP wafers using spatially resolved and polarization-resolved photoluminescence. These stresses have been identified as the stress fields around individual dislocations based on the match in shape and magnitude between calculated and observed stress patterns. This technique provides an accurate, nondestructive method of detecting and characterizing dislocations in InP and other luminescent semiconductors.

Holographic Investigation of Bone Response to Small Forces

The small forces used in orthodontic treatment when applied to a tooth, teeth or dental arches, generate stress which affects bone not only adjacent to the tooth but bone remote from the site of application of force. A technique employing holography has been devised to study quantitatively and qualitatively the observed stress pattern.

Comment on “The July 9 and 23, 1905, Mongolian earthquakes, a surface-wave investigation” by Emile Okal

We present an updated compilation of earthquake focal mechanisms in Brazil together with focal mechanisms from the sub-Andean region (mainly from global CMT catalogs). All earthquakes in the sub-Andean region show reverse (majority) or strike-slip faulting mechanisms. Focal mechanisms in Brazil show reverse, strike-slip and normal faulting. Focal mechanisms of nearby earthquakes in the same tectonic environment were grouped and inverted for the stress tensor. In the sub-Andean region, stresses are compressional, as expected, with the principal major compression (S1) roughly E-W, on average. A slight rotation of S1 can be observed and is controlled by the orientation of the Andean plateau. In the sub-Andean region, the intermediate principal stress (S2) is also compressional (i.e., larger than the lithostatic pressure, Sv), a feature that is not always reproduced in numerical models published in the literature. In mid-plate South America stresses seem to vary in nature and orientation. In SE Brazil and the Chaco-Pantanal basins, S1 tends to be oriented roughly E-W with S2 approximately equal to S3. This stress pattern changes to purely compressional (both SHmax and Shmin larger than Sv) in the São Francisco craton. A rotation of SHmax from E-W to SE-NW is suggested towards the Amazon region. Along the Atlantic margin, the regional stresses are very much affected by coastal effects (due to continent/ocean spreading stresses as well as flexural effects from sediment load at the continental margin). This coastal effect tends to make SHmax parallel to the coastline and Shmin (usually S3) perpendicular to the coastline. Few breakout data and in-situ measurements are available in Brazil and are generally consistent with the pattern derived from the earthquake focal mechanisms. Although numerical models of global lithospheric stresses tend to reproduce the main large-scale features in most mid-plate areas, the S1 rotation from ∼E-W in SE Brazil to SE-NW in the Amazon region are not well explained by the current numerical models. This means that the observed stress pattern in mid-plate South America should provide new insights into upper mantle dynamics, distinct from current global convection models.

An Analytical Description of Observed Stress Patterns on X-Ray Topographs of Silicon

An Analytical Description of Observed Stress Patterns on X-Ray Topographs of Silicon

Pressure Cell Observations—Garrison Dam Project

Pressure cells installed under a powerhouse and stilling basin indicate a reasonable agreement between the design assumptions and the observed values of stress distribution and seem to support the theoretical concept of high edge pressure. The pressure cells were installed to determine the relationship between vertical loads and the resulting foundation stresses in the Fort Union clay-scale. The results cover the period of construction and approximately 5 yr of operation after the completion of construction. The initial stress distribution is fairly equal under the structure, but as time passes, the edge pressures tend to increase, and their is a decrease of pressure in the central part of the foundation. The qualitative results since completion of the powerhouse indicate a reasonable agreement between the observed stress pattern and two assumed design stress patterns, one determined by rigorous analysis, and the other by an approximation.