Seismic source mechanism inversion from a linear array of receivers reveals non-double-couple seismic events induced by hydraulic fracturing in sedimentary formation

We developed a new method to invert source mechanisms of seismic events observed from a single (vertical or near vertical) array of receivers. This method was tested on a synthetic dataset and applied to a seismic dataset acquired during hydraulic fracturing of a sedimentary formation. We show that a crack-opening seismic event recorded on a single vertical array can be inverted as a pure shear seismic event, indicating that the best fitting shear mechanisms inverted from seismic data acquired along a vertical borehole provide misleading information. We found that the majority of the analyzed source mechanisms of the induced events are not consistent with pure shear faulting as previously thought. The non-shear source mechanisms are required even when seismic noise, location uncertainty, and uncertainty in the attenuation structural model are considered.     

Isotope and trace element evidence for depleted lithosphere in the source of enriched Ko’olau basalts

We have measured the Hf and Nd isotopic compositions of 38 basalts from the Ko’olau drill hole, Hawai’i. The basalts show limited variations in both ¹⁷⁶Hf/¹⁷⁷Hf and ¹⁴³Nd/¹⁴⁴Nd (ε _Nd varies from +4.2 to +7.3 and ε _Hf from +8.0 to +12.3). Their correlated variation has an R ² of 0.86. The data form an array with a slope of 1.2 on an ε _Hf–ε _Nd isotope correlation diagram, while the slope of all Hawai’ian basalt data is 0.98. Both slopes are significantly shallower than that of the mantle array of 1.4 defined by ocean island basalts. Previous studies have shown that a shallow slope in Hf–Nd isotope space can be related to ancient pelagic sediments in the mantle source (Blichert-Toft et al. 1999; Salters and White 1998). However, the combined variations in Ko’olau basalts of Hf–Nd–Pb–Os isotopic compositions and trace element ratios, such as La/Nb, Th/La and Sr/Nd, are not consistent with the simple addition of a sediment component to the mantle. We instead propose that the shallow slope on the Hf–Nd isotope correlation diagram for Ko’olau shield stage basalts can be better explained if the enriched endmember contains either an ancient oceanic lithosphere component or the high-¹⁷⁶Hf/¹⁷⁷Hf component observed in the Salt Lake Crater (SLC) peridotite xenoliths (which also have a depleted lithosphere origin). Since Ko’olau basalts have high ¹⁸⁷Os/¹⁸⁸Os (0.135–0.160) and the SLC xenoliths have ¹⁸⁷Os/¹⁸⁸Os up to 0.13 (Lassiter et al. 2000) Os-isotopes are consistent with the latter being a component in the enriched Ko’olau source.

---

How can stream bank erosion be predicted on small water courses? Verification of BANCS model on the Kubrica watershed

The current paper deals with the evaluation of the BANCS erosion prediction model and its two componentsethe Bank Erosion Hazard Index(BEHI)and Near-Bank Stress(NBS)indices.To construct the erosion prediction curves,18 experimental sections were established on the Kubrica Stream,district of Trencín,Slovakia.Each section was assessed through the NBS index and BEHI index and real annual bank erosion was measured using erosion toe pins.Subsequently,the relations between the BEHI and real annual bank erosion was assessed through regression and correlation analyses.The relation proved to be moderately strong,with the correlation coefficient(R)reaching 0.47.Further,the relation between the NBS index and real annual bank erosion was evaluated,which was also moderately strong,with R=0.65.Based on the measured data,two erosion prediction curves were constructed,the first for moderate BEHI,with R=0.69 and coefficient of determination(R2)of 0.47 and the second for high BEHI with R=0.74 and R2=0.55.The prediction curves were based on data from one year of measurements and can,therefore,be used only for discharges that occurred within that year and in the region where the model was developed.In the current case,according to runoff Curve Numbers(CN),the real culmination discharge was Q=1.88 m3/s,which is roughly equivalent to 1.5-year recurrence interval flow(Q1.5).     

The zooplankton communities of small water reservoirs with different trophic conditions in two catchments in western Slovakia

Our study summarizes data from six small water reservoirs in West Slovakia and analyzes the occurrence of zooplankton groups in relation to physico-chemical and catchment variables. The reservoirs are in two different catchments – of the Morava and Váh rivers. A total of 103 species were identified; 64 crustaceans (in both the pelagic and littoral zones) and 39 planktonic Rotifera in the pelagic zones. Significant differences were observed in species richness, abundance and biomass of planktonic crustaceans: 48 species were characteristic of the Váh catchment, while 53 were found in the Morava catchment. The density of zooplankton in the three reservoirs of the Váh River catchment ranged from 102 ind L^?1 to 21,488 ind L^?1 and the zooplankton biomass ranged from 0.12 mg L^?1 to 103.29 mg L^?1. The density of zooplankton in three Morava River catchment reservoirs ranged from 2 ind L^?1 to 3928 ind L^?1 and the zooplankton biomass ranged from 0.1 mg L^?1 to 27.3 mg L^?1. The differences were found to be related to catchment (altitude and catchment affiliation), chemical (BOD5, DO) and biological (Chromophyta, Chlorophyta) factors. Eutrophication of reservoirs in the Váh catchment was mainly due to agriculture and fish management, resulting in high nutrient concentrations. Species richness showed an unimodal response to BOD₅ and N-NH₄ with near optimum low values, 4.6 and 0.19 respectively. The relationship to oxygen content reflects preferences for less eutrophic waters and species richness tended to decrease with increasing DO and to decrease with increasing nutrient content.     

Distribution patterns of medicinal plants along an elevational gradient in central Himalaya, Nepal

This study aimed to compare the distribution patterns and trends of plant parts used among different groups of medicinal plants, geographical regions,and between medicinal plants and all vascular plants.We used the published sources for elevation records of 2,331 medicinal plant species to interpolate presence between minimum and maximum elevations and estimated medicinal plant richness for each 100-m elevational band. Monte Carlo simulations were used to test whether differences in elevational distribution between different groups of medicinal plants were significant. Total number of medicinal plants as well as different groups showed unimodal relationship with elevation. The elevational distributions of medicinal plants significantly differ between regions and between medicinal plant groups.When comparing the richness of all medicinal plants to all vascular plants,Monte Carlo simulations indicated that the numbers of medicinal plants are higher than expected at low elevations.The highest richness of medicinal plants at low elevation could be possibly due to favorable environmental factors such as high temperature, rainfall,sunlight or due to higher density of human population and thus higher pressure on use of any plants in lower elevations.     

Thermomechanical behavior of Pravcicka Brana Rock Arch (Czech Republic)

The paper discusses the results of research devoted to the preservation of a natural heritage site carried out at Pravcicka Brana Rock Arch, the largest natural sandstone bridge in Europe, located in the Bohemian Switzerland National Park, Czech Republic. One of the objectives of the study was to explore natural diurnal and annual temperature oscillations at the shallowest part of the rock mass and to acquire an insight into the heat balance both at the surface and within the rock mass. In 2009, four thermocouples were embedded at two positions (eastern and western sides) in a longitudinal direction sequence: rock surface and three different depths 0.10, 0.40, and 0.90 m. Calculation of heat flux inside the rock mass was treated with Fourier’s series which analyzes periodic temperature variation into a set of harmonics of the dominant diurnal or annual waves. Based on the results of Fourier’s analysis, fundamental thermophysical parameters were determined. These were used as the input data to establish a numerical model of temperature distribution in the near surface depth and thermomechanical (kinematic) behavior of the rock arch. Apart from in situ temperature monitoring data, the displacement time series data for the period 1993–2012 recorded by portable crack gauges in 1-month intervals were available. Finally, the rate of displacements in the model simulations was analyzed and compared with those recorded by on site displacement monitoring. Model simulations detected the existence of thermally driven deformation comprising both quasi-cyclic (reversible) movements and irreversible (plastic) deformations which in fact affirm the idea that temperature oscillations are the most contributing factor to the total displacement rate observed at the Pravcicka Brana Rock Arch. Based on the results of model simulation, the authors address the key issue whether the actual deformation mechanism and dynamics will have any influence on the stability of the Pravcicka Brana Rock Arch.     

Non-scaled analogue modelling of AMS development during viscous flow: A simulation on diapir-like structures

Development of magnetic fabric within a diapirically ascending columnar body was investigated using non-scaled analogue model made of plaster of Paris containing small amount of fine-grained homogeneously mixed magnetite. The apparatus for the modelling consists of a manual squeezer with calibrated spring and a Perspex container. Set of weak coloured layers at the bottom of the container was forced to intrude overlying fine-grained sand through a hole in a board attached to the squeezer. The development of AMS fabric is correlated with complex flow pattern indicated by coloured and originally horizontal plaster layers. Strongly constrictional and vertical fabric in the base and in the lower domain of the diapir resulting from convergent and upwards flows is overprinted by subhorizontal oblate fabrics due to vertical flattening and initial divergent flow in the apical parts. The measured AMS fabrics are compared with natural examples of magmatic stocks and dykes.     

Geodynamic hazard and risk assessments for sites close or in tectonic zones with shear movements

No region is excluded from actions of recent geodynamic short- or long-term effects which can be observed even on the Earth’s surface. The article delivers a geodynamic hazard assessment for the anthropogenic objects threatened by permanent shear movements occurring along tectonic faults and a way how to mitigate and/or eliminate the object risk. The proposed approach is applied to a case example of a motorway tunnel leading through rock masses where dynamically active zones with shear movements along their faults are expected. To detect the shear movements among rock masses, the contemporary satellite geodetic GPS methodology was used.     

Magnetic scanning and interpretation of paleomagnetic data from Prague Synform’s volcanics

Magnetic images have been produced at the distance of 0.1 mm from the polished basaltic thin sections of rocks from Prague Synform in Barrandian area. Three different magnetic textures were seen and when combined with optical imaging could be related to petrological features. The first magnetic texture revealed that most of the magnetic signature is localized within the amygdales formed later after the basalts became part of the sedimentary sequence. The second texture showed that the basaltic body contains large grain size distribution of magnetic carriers possibly with variable viscous magnetizations. The third texture suggested a presence of magnetic anisotropy of igneous origin. Such textural magnetic information along with the paleomagnetic characteristics of the basaltic rocks of Silurian age constrained the overall geological interpretation.