Cause of scale inconsistencies in DORIS time series

In this paper we analyze the scale of the DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) solutions with respect to DORIS extension of the International Terrestrial Reference Frame (ITRF) for Precise Orbit Determination DPOD2014. The main goal is to explain the scale inconsistencies and to find the optimal solution reaching low-biased and consistent scale time series. Our analysis profits from 4 different strategies based only on the Geodetic Observatory Pecný analysis center solution, using DORIS exchange format data 2.2. A difference in the sequence of the solutions directly corresponds to one of the changes in the solution settings: data elevation dependent weighting, application of data validity indicators and application of phase center - reference point correction. We process multi-satellite and single-satellite solutions for the time period 2011.0–2017.0. Our analysis examines scale inconsistency issues in 2011/2012 and in 2015. The scale increment in 2011/2012 is explained as a result of the concurrence of changes in satellite constellation and change in the provider data validity standards for Cryosat-2 and Jason-2 satellites. The scale increment in 2015 is explained as the effect of change in the standards for phase center - reference center corrections for Saral, Jason-2 and Cryosat-2 satellites. Moreover, comparing the solutions with and without elevation dependent data downweighting using the same elevation cutoff (10°), we found a significant reduction of scale bias and scale variation applying the data downweighting. The data downweighting improved also the station positioning repeatability. We demonstrate that the solution, which is completely free from the additional data associated with observations in DORIS exchange format 2.2 and includes the data downweighting law, eventuates in a consistent scale time series with the lowest offset with respect to DPOD2014 (version 1.0) (12.7 ± 2.3 mm for 2011.0–2017.0). The only remaining scale issue is the part of 2011/2012 increment of around 5 mm, explained by a change in the DORIS satellite constellation.     

Prevailing-frequency approximation of the coupling ray theory for electromagnetic waves or elastic S waves

The coupling–ray–theory tensor Green function for electromagnetic waves or elastic S waves is frequency dependent, and is usually calculated for many frequencies. This frequency dependence represents no problem in calculating the Green function, but may represent a great problem in storing the Green function at the nodes of dense grids, typical for applications such as the Born approximation. This paper is devoted to the approximation of the coupling–ray–theory tensor Green function, which practically eliminates this frequency dependence within a reasonably broad frequency band.     

Effects of 1-D versus 3-D velocity models on moment tensor inversion in the Dobrá Voda area in the Little Carpathians region,Slovakia

Retrieving the parameters of a seismic source from seismograms involves deconvolving the response of the medium from seismic records. Thus, in general, source parameters are determined from both seismograms and the Green functions describing the properties of the medium in which the earthquake focus is buried. The quality of each of these two datasets is equally significant for the successful determination of source characteristics. As a rule, both sets are subject to contamination by effects that decrease the resolution of the source parameters. Seismic records are generally contaminated by noise that appears as a spurious signal unrelated to the source. Since an improper model of the medium is quite often employed, due to poor knowledge of the seismic velocity of the area under study, and since the hypocentre may be mislocated, the Green functions are not without fault. Thus, structures not modelled by Green functions are assigned to the source, distorting the source mechanism. To demonstrate these effects, we performed a synthetic case study by simulating seismic observations in the Dobrá Voda area of the Little Carpathians region of Slovakia. Simplified 1-D and 3-D laterally inhomogeneous structural models were constructed, and synthetic data were calculated using the 3-D model. Both models were employed during a moment tensor inversion. The synthetic data were contaminated by random noise up to 10 and 20 % of the maximum signal amplitude. We compared the influence of these two effects on retrieving moment tensors, and determined that a poor structural model can be compensated for by high-quality data; and that, in a similar manner, a lack of data can be compensated for by a detailed model of the medium. For examples, five local events from the Dobrá Voda area were processed.     

Automatic tracing of the foot of the continental slope

The UNCLOS III (Article 76, Section 4(b)) defines the foot of the continental slope as the point of maximum change in the gradient at its base. It is impossible to locate so defined afoot and thus to trace the foot‐line objectively by eye. In this study we show a method designed automatically to detect and trace the foot‐line of the continental slope from an irregular array of bathymetrical data. Our algorithm first transforms the bathymetric surface to a maximum curvature surface. On this new surface, the foot‐line corresponds to one of the ridges; instead of tracing the foot‐line on the bathymetric surface, we now can trace the ridges on the maximum curvature surface. The tracing of the ridges can be done automatically and objectively and the foot‐line is identified as being one of these ridges. We devote particular attention to the case when the ridge‐line is not defined, i.e., to the case when the point of maximum gradient change becomes a region of maximum gradient change.     

A new approach to modeling perpendicular fabrics in porphyritic plutonic rocks using the finite element method

A growing body of field evidence indicates that hypersolidus fabrics preserved in syntectonic plutons are likely to have formed in highly crystallized ‘rigid sponge’ magma. This paper demonstrates that such magma could be idealized as a rheological solid and that the development of non-coaxial fabrics in plutonic rocks can very conveniently be modeled in the framework of solid mechanics. Using the finite element method (FEM), we modeled two strain regimes of small magnitudes (plane-strain horizontal simple shear with the shear strain γ of up to 0.30 and plane-strain pure shear of up to 15% shortening) superposed onto vertically oriented and variously spaced elastic phenocrysts set in the viscoelastic matrix. In the simple shear regime, the phenocrysts slightly rotate toward the shear plane, while the principal strain directions in the matrix are instantaneously oriented at an angle of about 45° or less to the phenocryst fabric. Simple shear thus can only lead to the formation of oblique phenocryst and matrix fabrics. By contrast, the vertical phenocryst fabric is maintained in the pure shear regime, and a new horizontal fabric can develop almost instantaneously in the matrix even for small amounts of superposed shortening (5% shortening after 10 ky in our model). We conclude that such a mechanism can easily produce perpendicular hypersolidus fabrics in plutonic rocks and that only a very short time span (first thousands of years) is required to develop magmatic fabric in a pluton for ‘normal’ rates (10⁻¹⁵ to 10⁻¹³ s⁻¹) of tectonic deformation.     

Shear wave crustal velocity model of the Western Bohemian Massif from Love wave phase velocity dispersion

We propose a new quantitative determination of shear wave velocities for distinct geological units in the Bohemian Massif, Czech Republic (Central Europe). The phase velocities of fundamental Love wave modes are measured along two long profiles (~200 km) crossing three major geological units and one rift-like structure of the studied region. We have developed a modified version of the classical multiple filtering technique for the frequency-time analysis and we apply it to two-station phase velocity estimation. Tests of both the analysis and inversion are provided. Seismograms of three Aegean Sea earthquakes are analyzed. One of the two profiles is further divided into four shorter sub-profiles. The long profiles yield smooth dispersion curves; while the curves of the sub-profiles have complicated shapes. Dispersion curve undulations are interpreted as period-dependent apparent velocity anomalies caused both by different backazimuths of surface wave propagation and by surface wave mode coupling. An appropriate backazimuth of propagation is found for each period, and the dispersion curves are corrected for this true propagation direction. Both the curves for the long and short profiles are inverted for a 1D shear wave velocity model of the crust. Subsurface shear wave velocities are found to be around 2.9 km/s for all four studied sub-profiles. Two of the profiles crossing the older Moldanubian and Teplá-Barrandian units are characterized by higher velocities of 3.8 km/s in the upper crust while for the Saxothuringian unit we find the velocity slightly lower, around 3.6 km/s at the same depths. We obtain an indication of a shear wave low velocity zone above Moho in the Moldanubian and Teplá-Barrandian units. The area of the Eger Rift (Teplá-Barrandian–Saxothuringian unit contact) is significantly different from all other three units. Low upper crust velocities suggest sedimentary and volcanic filling of the rift as well as fluid activity causing the earthquake swarms. Higher velocities in the lower crust together with weak or even missing Moho implies the upper mantle updoming.     

Palynological and geochemical response to environmental changes in the Lower Cretaceous in the Outer Western Carpathians; a record from the Silesian unit, Czech Republic

Rich dinoflagellate cyst assemblages recorded from the Vendryne Formation, Tesin Limestone, and Hradiste Formation of the Silesian unit, Czech Republic are presented. The results of a qualitative and quantitative study of dinoflagellate cysts are presented and discussed. Age-assessment of the sediments based on 86 species suggests a Late Tithonian to Early Berriasian age for the Vendryne Formation and a Late Berriasian (Otopeta Ammonite Zone) to the basal part of the Late Valanginian (Verrucosum Ammonite Zone) age for the Tesin Limestone. Pelitic flyschoid sediments of the Hradiste Formation belong to the Late Valanginian - Early Hauterivian age. Quantitative palynological study and carbon isotope analysis were applied to understand the change from the grey clays to dark grey clays sedimentation. The dinoflagellate cyst assemblages show deposition in a shallow-sea environment. An increasing amount of sporomorphs towards the overlying layers (they are the most abundant in the Hradiste Formation) shows a growing supply of terrestrial material at the same time. The values of δ¹³C increased significantly from a level of 0.43 or 0.75-1.81‰ in the Late Valanginian. This change probably indicates an increase in organic matter storage and perturbation of the carbon cycle connected with the dark grey clays sedimentation.     

Recent Climate Warming: Surface Air Temperature Series and Geothermal Evidence

Long-term (1961 – 1996) meteorological air temperature series together with the reconstructed ground surface temperature histories, obtained by inverting borehole temperature-depth profiles, were used to project regional patterns of the recent (climate) warming rate on the territory of the Czech Republic. The characteristic magnitude of the warming rate of 0.02 –0.03 K/yr was confirmed by the results of several years of monitoring the temperature in two experimental boreholes. The monitoring of shallow temperatures at depths of about 30 –40 m, i.e. below the reach of the seasonal surface temperature variations, can serve as an alternative tool of direct quantitative assessment of the present warming rate. The data also seem to sustain a potential man-made component contributing to the more pronounced recent warming rate observed in the areas of large agglomeration.