Über Beanspruchung und Verformung von Gesteinen     

Prof. Dr. F. Karl  Dr. H. Kern 《Contributions to Mineralogy and Petrology》1968,18(3):199-224

7 coaxial (p ₁>p ₂=p ₃) and 6 real triaxial (p ₁>p ₂>p ₃) compression tests (0,5 to 6 hours duration) on cubic samples of homogeneous, statistically low anisotropic marble from Auerbach (Germany) were made at room temperature and different ratios of the main pressures and rates of loading. 3 samples of strong anisotropic marble of Drama (Greece) were deformed at p ₁p ₂p ₃=841 and constant rate of loading in the three orientations: parallel, at 45° and perpendicular to the foliation (12 hours duration). As can be deduced from the orientation diagrams, the deformation proceeds mainly by twin gliding. In most of the tests reported here the symmetry of the external loading (coaxial or orthorhombic) can be correlated with the symmetry of the orientation diagrams. Real triaxial deformation (P ₁Nep ₂Nep ₃) produces two sets of planes ± perpendicular to each other as B B. In the tests with the strong anisotropic material the strain was measured in the three main directions and plotted as strain-time curves. When the foliation is oriented perpendicularly or even obliquely to p ₁ compression dominates at the beginning in the direction of the intermediate loading p ₂ producing preferred orientation of the twin lamellae. Later on there is compression in p ₁ and extension in p ₂ and p ₃. This phase of deformation is characterized by brittle fracture and increase of volume.  相似文献   

Über Beanspruchung und Verformung von Gesteinen     

Prof. Dr. F. Karl  Dr. H. Kern 《Contributions to Mineralogy and Petrology》1968,18(3):225-240

A new real triaxial deformation apparatus for p ₁p ₂p ₃ tests and temperatures up to 700° C has been developed. In five creep tests over 8 hours the strain-time curves at 650° C for axial and orthorhombic symmetry of stress are plotted in the three main directions and compared with the petrofabric diagrams of the deformed material. In all tests the symmetry of the petrofabrics can be correlated with the symmetry of the external loading. From the strain-time curves it can be deduced that the intermediate loading p ₂ is of great influence in the stress-strain behavior.Syntectonic recrystallization is found to be common for all tests in the form of broad lensoid and irregular defined {01¯12} lamellae oriented favorably for twinning. Measurements of c-axes in newly recrystallized grains show preferential alingnement subparallel to the axis of maximum principal loading.

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Der Deutschen Forschungsgemeinschaft sei für die finanzielle Unterstützung der Untersuchungen besonders gedankt.  相似文献   

On geoid determination from airborne gravity     

P. Novák  M. Kern  K.-P. Schwarz  M.G. Sideris  B. Heck  S. Ferguson  Y. Hammada  M. Wei 《Journal of Geodesy》2003,76(9-10):510-522

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October 2003     

Katherine Stone  Orville Magoon  Billy Edge  Lesley Ewing 《Environmental Geology》2003,44(7):876-875

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Structure-configurational entropy and its effect on the thermodynamic stability of uranyl phases: With special application for geological disposal of nuclear waste     

陈繁荣  Rodney C.Ewing 《中国科学D辑(英文版)》2003,46(1)

Uranyl phases are found as the alteration products of uraninite under oxidizing condi- tions[1—3]. They are also expected to be the dominant alteration products of spent UO2 fuel in an oxidizing environment, such as at nuclear waste repositories[4—8]. …  相似文献   

Alpha-decay damage in minerals of the pyrochlore group     

Gregory R. Lumpkin  Rodney C. Ewing 《Physics and Chemistry of Minerals》1988,16(1):2-20

X-ray diffraction analysis and transmission electron microscopy have been used to study the effects of alpha-decay damage in pyrochlore group minerals, characterized by the general formula A _1?m B ₂O₆(O,OH,F)_1?n ·pH₂O. As defined by the XRD intensity ratio I/I ₀ , both the saturation dose (for which I/I ₀ =0.1?0.0) and the dose which signifies the initial loss of crystallinity (for which I/I ₀ =1.0?0.8) increase as a function of geologic age. The increase is attributed to annealing of isolated alpha-recoil tracks back to the original crystalline structure. The tracks have calculated mean lives, τ_a, on the order of 10⁸ years. In contrast, minerals which remain crystalline (e.g., uraninite, UO₂) despite doses of up to 10¹⁸ alpha-events/mg have mean alpha-recoil track lives ≈10⁴ years (Eyal and Fleischer 1985). After correcting the calculated dose for annealing of alpha-recoil damage, I/I ₀ is observed to decrease exponentially to zero over the dose range 0.02–1.0 × 10¹⁶ alpha-events/mg. The relationship between I/I ₀ and “corrected” dose was used to calculate an average alpha-recoil track diameter of 4.6 nm, in which < 2600 atoms are displaced. XRD line broadening due to strain dominates the first half of the crystalline-to-metamict transition, reaching a maximum of 0.003, then decreasing to < 0.001. Line broadening due to decreasing crystallite size dominates the latter half of the transition. Estimated crystallite dimensions decrease from 450 nm to < 15 nm prior to reaching the fully metamict state. With increasing dose HRTEM images of microlites from the Harding pegmatite sequentially exhibit: 1) mottled diffraction contrast, 2) isolated 1–5 nm aperiodic areas, 3) coexisting aperiodic and crystalline areas, 4) relict “islands” of crystalline material in an aperiodic matrix, and 5) complete loss of lattice fringe periodicity. With no consideration given to alpha-recoil track fading, the transition covers a dose range of 0.04–1.7 × 10¹⁷ alpha-events/mg. Using a value of τ_a=10⁸ years, this dose range is corrected down to 0.02–1.2 × 10¹⁶ alpha-events/mg. The metamict state is characterized by a range of M-M and M-O distances which give rise to bands of diffuse scattering centered at 0.30 nm and 0.18 nm, respectively, in x-ray and electron diffraction patterns. Random image contrast shown by HRTEM is consistent with a random network type structure, an interpretation supported by EXAFS/XANES studies (Greegor et al. 1985a, b, 1987). The structure of metamict pyrochlore consists of an aperiodic framework of corner-sharing B-O polyhedra. Compared to the crystalline precursor, the metamict state displays a reduced M-O coordination number and mean bond length, increased distortion of the B-site, and a slight increase in the average M-M distance.  相似文献   

The effect of a deviatoric stress on physical rock properties     

H. Kern  T. Popp  R. Schmidt 《Surveys in Geophysics》1994,15(5):467-479

Petrophysical measurements were carried out on dry specimens of mica-gneiss, amphibolite and serpentinite from KTB core samples and samples of surface outcrops in order to determine the effect that a deviatoric stress field, as observed at the KTB area, may have on the in-situ rock properties. Simulating the variation of the actual principal stresses and temperature with depth, seismic wave velocities, densities, linear and volumetric strain (porosity) have been measured, taking into account the overall spatial orientation of the foliation at the KTB area with respect to the principal stress axes. Comparison with respective data evaluated for lithostatic pressure conditions revealed that the stress-related (crack-related) effect on wave velocities respectively on velocity anisotropy is in the range 1–3%, due to microcracks which are selectively closed or kept open by the deviatoric stress. The effect of the deviatoric stress is particularly documented by shear wave splitting due to microfractures that are oriented normal to the minimum principal stress axis.  相似文献   

Power from sea waves: Edited by B. CountAcademic Press,London, 1980, 449 pp., £26.40/$57.00     

J.A. Ewing 《Estuarine, Coastal and Shelf Science》1982,15(3):346-347

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Local housing price index analysis in wind-disaster-prone areas     

Bradley T. Ewing  Jamie B. Kruse  Yongsheng Wang 《Natural Hazards》2007,40(2):463-483

This study examines the effect of severe wind events on the mean and variance of housing price indices of six metropolitan statistical areas (MSA) that are vulnerable to hurricanes and/or tornadoes. The research focuses on three areas that experienced significant tornado activity (Fort Worth-Arlington, Nashville, and Oklahoma City) and three hurricane-prone areas (Corpus Christi, Miami, and Wilmington, NC). An econometric time series model that captures the housing market responses to severe windstorms is utilized. The model estimates changes in the local housing price index (HPI) as a function of several control variables as well as dichotomous variables that correspond to the tornadoes and hurricanes. As expected, the statistical findings indicate an immediate but short-lived decline in housing prices following a tornado or hurricane. Somewhat surprising is the result that the impact on the housing market is remarkably consistent whether the wind event was a hurricane or a tornado. Hurricanes and tornadoes are vastly different in terms of the point probabilities of a hit, the scope of the affected area and the lead time that supports last minute preparation to mitigate damage. It appears that the market response to destruction of real property does not distinguish between the types of wind event that produced the damage to the region. Results suggest that windstorms result in an immediate one-half to two percent reduction in total MSA housing value. This corresponds to a range of $34 million to $580 million in lost housing value. Estimates indicate some differences in how long market values continue to decline in the periods following the wind event; however, most of the decline occurs within four quarters after the windstorm. These differences can be attributed to the particular time series characteristics of the specific housing markets and their respective housing price indices. The market serves the purpose of integrating and normalizing the losses. In so doing the market provides a metric— a method for calibrating and comparing structural damage caused by different phenomenon.

Yongsheng WangEmail:

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Low-temperature anisotropic diffusion of helium in zircon: Implications for zircon (U-Th)/He thermochronometry     

Martin Reich  Rodney C. Ewing  Udo Becker 《Geochimica et cosmochimica acta》2007,71(12):3119-3130

In the last decade the zircon (U-Th)/He (ZHe) thermochronometer has been applied to a variety of geologic problems. Although bulk diffusion coefficients for He in zircon are available from laboratory step-heating experiments, little is known about the diffusion mechanism(s) and their dependence on the crystallographic structure of zircon. Here, we investigate the diffusion of He in perfectly crystalline zircon using atomistic simulation methods that provide insights into the structural pathways of He migration in zircon. Empirical force fields and quantum-mechanical calculations reveal that the energy barriers for He diffusion are strongly dependent on structure. The most favorable pathway for He diffusion is the [0 0 1] direction through the open channels parallel to the c-axis (, activation energy for tracer diffusion of a He atom along [0 0 1]). In contrast, energy barriers are higher in other directions where narrower channels for He diffusion are identified, such as [1 0 0], [1 0 1], and [1 1 0] (ΔE^∗ of 44.8, 101.7, and 421.3 kJ mol⁻¹, respectively). Molecular dynamics simulations are in agreement with these results and provide additional insight in the diffusion mechanisms along different crystallographic directions, as well as the temperature dependence. Below the closure temperature of He in zircon [T_c ∼ 180 °C, Reiners P. W., Spell T. L., Nicolescu S., and Zanetti K. A. (2004) Zircon (U-Th)/He thermochronometry: He diffusion and comparisons with Ar-40/Ar-39 dating. Geochim. Cosmochim. Acta68, 1857-1887], diffusion is anisotropic as He moves preferentially along the [0 0 1] direction, and calculated tracer diffusivities along the two most favorable directions differ by approximately five orders of magnitude (D_[001]/D_[100] ∼ 10⁵, at T = 25 °C). Above this temperature, He atoms start to hop between adjacent [0 0 1] channels, along [1 0 0] and [0 1 0] directions (perpendicular to the c-axis). The diffusion along [1 0 0] and [0 1 0] is thermally activated, such that at higher temperatures, He diffusion in zircon becomes nearly isotropic (D_[001]/D_[100] ∼ 10, at T = 580 °C). These results suggest that the anisotropic nature of He diffusion at temperatures near the closure temperature should be considered in future diffusivity experiments. Furthermore, care should be taken when making geologic interpretations (e.g., exhumation rates, timing of cooling, etc.) from this thermochronometer until the effects of anisotropic diffusion on bulk ages and closure temperature estimates are better quantified.  相似文献