Constrains on stresses in isotropic homogeneous infinite half-spaces being in welded contact: 2D anti-plane and in-plane cases

Formulas are derived for two-dimensional problems relating stresses across a plane boundary that divides infinite homogeneous half-spaces being in welded contact. The calculations are made for both anti-plane and in-plane stress cases. The results obtained for the former case that involve only two stress components are useful in the analysis of fracture of strike-slip type. For the in-plane case, the relations that link stresses in one half-space with the corresponding homogeneous stresses in the other half-space are presented for arbitrarily oriented shear and normal stresses and for the center of compression (dilatation). The above relations provide a compete set of expressions that, among other things, make it possible to analyze stresses involved in faulting of deep-slip type in an inhomogeneous medium. The quantitative preliminary evaluations based on the results obtained demonstrate the great role of low rigidity media in fracture processes of all kinds within the Earth’s crust.     

Consistency of seven different GNSS global ionospheric mapping techniques during one solar cycle

In the context of the International GNSS Service (IGS), several IGS Ionosphere Associated Analysis Centers have developed different techniques to provide global ionospheric maps (GIMs) of vertical total electron content (VTEC) since 1998. In this paper we present a comparison of the performances of all the GIMs created in the frame of IGS. Indeed we compare the classical ones (for the ionospheric analysis centers CODE, ESA/ESOC, JPL and UPC) with the new ones (NRCAN, CAS, WHU). To assess the quality of them in fair and completely independent ways, two assessment methods are used: a direct comparison to altimeter data (VTEC-altimeter) and to the difference of slant total electron content (STEC) observed in independent ground reference stations (dSTEC-GPS). The main conclusion of this study, performed during one solar cycle, is the consistency of the results between so many different GIM techniques and implementations.     

Remote Sensing Data in Wind Velocity Field Modelling: a Case Study from the Sudetes (SW Poland)

The phenomena of wind-field deformation above complex (mountainous) terrain is a popular subject of research related to numerical modelling using GIS techniques. This type of modelling requires, as input data, information on terrain roughness and a digital terrain/elevation model. This information may be provided by remote sensing data. Consequently, its accuracy and spatial resolution may affect the results of modelling. This paper represents an attempt to conduct wind-field modelling in the area of the ?nie?nik Massif (Eastern Sudetes). The modelling process was conducted in WindStation 2.0.10 software (using the computable fluid dynamics solver Canyon). Two different elevation models were used: the Global Land Survey Digital Elevation Model (GLS DEM) and Digital Terrain Elevation Data (DTED) Level 2. The terrain roughness raster was generated on the basis of Corine Land Cover 2006 (CLC 2006) data. The output data were post-processed in ArcInfo 9.3.1 software to achieve a high-quality cartographic presentation. Experimental modelling was conducted for situations from 26 November 2011, 25 May 2012, and 26 May 2012, based on a limited number of field measurements and using parameters of the atmosphere boundary layer derived from the aerological surveys provided by the closest meteorological stations. The model was run in a 100-m and 250-m spatial resolution. In order to verify the model’s performance, leave-one-out cross-validation was used. The calculated indices allowed for a comparison with results of former studies pertaining to WindStation’s performance. The experiment demonstrated very subtle differences between results in using DTED or GLS DEM elevation data. Additionally, CLC 2006 roughness data provided more noticeable improvements in the model’s performance, but only in the resolution corresponding to the original roughness data. The best input data configuration resulted in the following mean values of error measure: root mean squared error of velocity = 1.0 m/s and mean absolute error of direction = 30°. The author concludes that, within specific meteorological conditions (relatively strong and constant synoptic forcing) and using the aforementioned input data, the Canyon model provides fairly acceptable results. Similarly, the quality of the presented remote sensing data is suitable for wind velocity modelling in the proposed resolution. However, CLC 2006 land use data should be first verified with a higher-resolution satellite or aerial imagery.     

On faulting in a medium containing an inhomogeneity inplane and antiplane strain models

Faulting in a medium with an inhomogeneity is analysed applying two-dimensional models consisting of a shear crack in a presence of a circular inclusion. The stress drop and the stress intensity factor are calculated for mode II and III cracks of various positions in relation to the inclusion. The results demonstrate that the effect of an inhomogeneity on a shear zone strongly depends on the location of a zone for either mode II or mode III shear zone. This effect is mostly due to the spatial distribution of external effective shear stress around an inhomogeneity. Depending on the position, an inhomogeneity may have either a destabilizing effect (the stress intensity factor becomes greater) or a stabilizing influence (the stress intensity factor is decreased or faulting is prohibited so the inhomogeneity acts as an asperity or a barrier). There is a substantial difference, however, between mode II and mode III shear zones approaching an inhomogeneity centrally. Namely, the effect of inhomogeneity on the mode III shear zone located in the immediate vicinity of the inhomogeneity is in this case considerably more pronounced than that for mode II shear zone and depends to a far greater extent on the rigidity contrast between the inhomogeneity and the surrounding medium. Another important conclusion is that the quantitative effect of an inhomogeneity on faulting depends essentially on the initial value of the stress drop of a shear zone approaching an inhomogeneity, being decidedly higher for a shear zone of small stress drop. It means that in specified areas in the proximity of medium inhomogeneities one should expect substantially greater faulting activity in which weak events prevail than in other regions surrounding inhomogeneities where such activity should be distinctly reduced. Such conclusions apply to both high rigidity inhomogeneities, which, in particular, may be associated with intrusions from the upper mantle, and to low rigidity inhomogeneities such as volcanos. The present model sets forth the plausible explanation regarding why earthquakes from the same region are occasionally characterized by various values of the stress drop. The model also presents the quantitative insight concerning how heterogeneity of the medium, in the sense of spatial variation of elastic constants, affects faulting.