Apparent stress scaling and statistical trends     

Piotr Senatorski   《Physics of the Earth and Planetary Interiors》2007,160(3-4):230-244

Statistical relations between different earthquake parameters, such as M₀ (seismic moment), E_S (seismic energy), τ_a (apparent stress), A (rupture area), g (average slip acceleration), are investigated. For this purpose, a kinematic earthquake model representing averaged earthquake rupture process is formulated. The model implies a scaling relationship for τ_a as a function of three other parameters, related to kinematic (M₀), geometric (A) and material (g) source characteristics, which, according to the model, can change independently. This scaling relation is used to explain statistical trends that characterize different earthquake data sets (including micro-, small, moderate and large events) plotted in the log τ_a − log M₀ space, and to determine the area in this space, where typical earthquakes occur. The scaling relationship is interpreted in terms of the apparent stress minimum (i.e., the most uniform among the possible earthquake rupture patterns). It is concluded that, although the apparent stress increases on an average with increasing seismic moment, small and large earthquakes are essentially similar.  相似文献   

Modelling the variability of the Fe Kα line in accreting black holes     

Piotr T. &#;ycki 《Monthly notices of the Royal Astronomical Society》2004,351(4):1180-1186

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Fractal Approach,Analysis of Images and Diagenesis in Pore Space Evaluation     

Grzegorz?Lesniak  Piotr?SuchEmail author 《Natural Resources Research》2005,14(4):317-324

Simple net model constructed by authors, facies analysis and compaction models, were applied to evaluate reservoir properties of sandstone facies of the Carpathian Flysch (the Istebna sandstones). The applied net model was built on the base of fractal approach proposed by Don Turcotte in 1977 and computer analysis of images. Laboratory measurements include porosity, density, permeability to nitrogen, mercury injection capillary pressure tests, and microscopic analysis of thin sections. D.W. Houseknecht's theory, proposed in 1987, was applied for compaction and cementation modeling. The residual saturation data were used to validate obtained results. Net model allows an evaluation of filtration properties of analyzed sandstones and to distinguish the classes of similarity of pore space. The extracted parameters of classes of similarity were correlated with facies scheme of the investigated geological structure. Influence of compaction and cementation on pore space parameters was discussed.  相似文献   

Till kinematics in the Stargard drumlin field,NW Poland constrained by microstructural proxies     

Piotr Hermanowski  Jan A. Piotrowski  Piotr Duda 《第四纪科学杂志》2020,35(7):920-934

Deciphering the relationships between streamlined subglacial landforms and deposits therein helps to constrain the dynamics of past ice sheets. Here we present microstructural analyses of till from the largest drumlin field in the North European Lowland generated by a major palaeo-ice stream of the Scandinavian Ice Sheet. Data derived from thin sections and X-ray microtomography (μCT) reveal multiple microstructures including microshears, circular structures, grain stacks and crushed grains. Long axes of micro-clasts measured in thin sections are directionally clustered and have low, down-ice-oriented dip angles. Some samples reveal subordinate clustering oriented at high angles to the main direction. The μCT data show low clustering strengths of clasts and no systematic fabric pattern in the entire set of samples. There is no correspondence between the clast orientations and the directions of drumlin long axes, suggesting that the till is antecedent in relation to the drumlin-shaping process. The observations indicate spatially and temporally variable, shallow-seated brittle and ductile deformation controlled by porewater pressure fluctuations and generated time-transgressively parallel to till accretion. Consistently with previous studies, the data suggest that the Stargard drumlins are erosional remnants of a pre-existing terrain shaped by material removal from the inter-drumlin areas.  相似文献   

Water chemistry and hydrometeorology in a glacierized catchment in the Polar Urals,Russia     

Łukasz Stachnik  Piotr Wałach  Łukasz Uzarowicz  Jacob C. Yde  Zornitza Tosheva  Dominika Wrońska-Wałach 《山地科学学报》2014,11(5):1097-1111

This study aims to determine the relationships between local meteorological conditions,proglacial river discharge and biogeochemical processes operating in a periglacial basin located in the Polar Ural mountain range, Russia. Fieldwork was conducted in the catchment of Obruchev Glacier(13 km2) during the summer peak flow period in 2008. River discharge was dominated by snowmelt and changed from 3300 l s-1 to less than 1000 l s-1. The mean daily air temperatures of stations situated in the mountain tundra and near Obruchev Glacier from July 11 th to August 1st 2008 were 14.4°C and 10.3°C, respectively. The glacial river had low total dissolved solids varying from 4.5 to 9 mg l-1 and coefficients of correlation between Na+ and Cl-, K+ and Cl-, as well as NH4+ and Cl- were 0.94, 0.90 and 0.84, respectively. Rainfall events affected the snowmelt initiation and provided an essential part of the discharge during the intense snowmelt period, which occurred from July 11 th to July 18 th 2008. Data showed that Na+ and K+ in the surface water derived from snowmelt rather than chemical weathering of silicates. Also, it was obtained that NO3- derived from the melting snowpack, whereas ammonification occurring under the snowpacks was the primary source for NH4+.  相似文献   

The initial stages of cave formation: Beyond the one-dimensional paradigm     

Piotr Szymczak  Anthony J.C. Ladd 《Earth and Planetary Science Letters》2011,301(3-4):424-432

The solutional origin of limestone caves was recognized over a century ago, but the short penetration length of an undersaturated solution made it seem impossible for long conduits to develop. This is contradicted by field observations, where extended conduits, sometimes several kilometers long, are found in karst environments. However, a sharp drop in the dissolution rate of CaCO₃ near saturation provides a mechanism for much deeper penetration of reactant. The notion of a “kinetic trigger” – a sudden change in rate constant over a narrow concentration range – has become a widely accepted paradigm in speleogenesis modeling. However, it is based on one-dimensional models for the fluid and solute transport inside the fracture, assuming that the dissolution front is planar in the direction perpendicular to the flow. Here we show that this assumption is incorrect; a planar dissolution front in an entirely uniform fracture is unstable to infinitesimal perturbations and inevitably breaks up into highly localized regions of dissolution. This provides an alternative mechanism for cave formation, even in the absence of a kinetic trigger. Our results suggest that there is an inherent wavelength to the erosion pattern in dissolving fractures, which depends on the reaction rate and flow rate, but is independent of the initial roughness. In contrast to one-dimensional models, two-dimensional simulations indicate that there is only a weak dependence of the breakthrough time on kinetic order; localization of the flow tends to keep the undersaturation in the dissolution front above the threshold for non-linear kinetics.  相似文献   

Numerical simulations of three-dimensional magnetic swirls in a solar flux-tube     

Piotr Chmielewski  Krzysztof Murawski  Alexandr A.Solov’ev 《中国天文和天体物理学报》2014,(7):855-863

We aim to numerically study evolution of Alfv′en waves that accompany short-lasting swirl events in a solar magnetic flux-tube that can be a simple model of a magnetic pore or a sunspot. With the use of the FLASH code we numerically solve three-dimensional ideal magnetohydrodynamic equations to simulate twists which are implemented at the top of the photosphere in magnetic field lines of the flux-tube. Our numerical results exhibit swirl events and Alfv′en waves with associated clockwise and counterclockwise rotation of magnetic lines, with the largest values of vorticity at the bottom of the chromosphere, and a certain amount of energy flux.  相似文献   

The estimation of the mean density in the Universe     

Piotr Flin 《Astrophysics and Space Science》1982,83(1-2):437-439

The mean density of matter, as estimated from deep optical samples of galaxies, is too low to close the Universe. However, some additional considerations do not exclude such a possibility.  相似文献   

The Electrostatic Blow-Off of Cometary Grains and Variations and Outbursts of Brightness of Comets at Large Heliocentric Distances     

Piotr Gronkowski 《Astrophysics and Space Science》2004,294(3-4):135-150

Interaction between the strong solar wind and the dark side of a cometary nucleus was considered. It was calculated that the potential of the dark side of the cometary nucleus could be numerically large and negative. Assuming that the nucleus of the comet has surface mantle which consists of loose, fine dust-ice particles, it was shown that cometary particles could electrostatically levitate over the nucleus. It was examined how this phenomenon affected the changes in the cometary brightness. Calculations were carried out for realistically assumed values of a large range of cometary parameters. It was shown that the considered mechanism could lead to the variations of cometary brightness, sometimes even to the outbursts of brightness.  相似文献   

Directional Distribution of Observable Comets Induced by A Star Passage Through the Oort Cloud     

Piotr A. Dybczyński 《Earth, Moon, and Planets》2002,90(1-4):483-488

We simulated the passage of a star through the Oort cometary cloud andanalyzed the resulting sample of observable long period comets, noting strong asymmetries in the directional distribution of the perihelion points of thosecomets. We discuss the results previously published byWeissman (1996) for the same case. An explanation is suggestedwhy the isotropic output can be obtained only for a very peculiar case. The``cometary shower' density variation with time is also presented and thetime-dependence of the directional distribution is discussed.  相似文献