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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.     

沿海地区区域投资环境的综合评价

中国沿海地区经济持续高速的发展,很大程度上得益于外国投资。吸引外资、刺激经济增长的关键在于不断地改善局部投资环境。文章的宗旨是对中国沿海主要经济发展地区的投资环境进行对比研究。运用层次分析方法,作者得到了一些有益的结论。     

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.     

Montagne Pelée volcano (Martinique,in the French Lesser Antilles) hydrogeological system revealed by high-resolution helicopter-borne electromagnetic imagery

Montagne Pelée, on the French island of Martinique, eastern Caribbean Sea, has been one of the deadliest volcanoes in the world, with 30,000 victims following the 1902 eruption. Thousands of people still live nearby, and this volcano is a strategic “water tank” for Martinique Island, providing 40% of the island’s water supply. This research aimed to better understand its hydrogeological functioning and the relationship with its complex volcanological evolution, taking advantage of a high-resolution helicopter-borne geophysical survey correlated with hydrogeological data from the boreholes and springs databases. Electromagnetic data, correlated with hydrogeological data, allowed for the identification of unsaturated zones, aquifers, and seawater intrusions, as well as the main geological units. In addition, data synthesised from pumping tests revealed that the older the unconsolidated pyroclastic deposits, the lower their hydraulic conductivity. The structural asymmetry between the northeastern and southwestern volcano flanks impacts its hydrogeological functioning. Consequently, the Montagne Pelée hydrogeological conceptual model is marked by several distinguishable aquifers. The upper perched aquifer within recent lava domes is directly involved in, and impacted by, phreatic eruptions, and it supports low flowrate springs. The remaining effective rainfall infiltrates to depth and recharges the hydrothermal system through vertical fractures. The other aquifers are categorized into three groups: northeastern, southeastern and southwestern flank aquifers. This research is a new step toward a better understanding of the Lesser Antilles volcanoes and more broadly of the central and proximal parts of the andesitic active volcanoes.

     

Ground water radon anomalies in Bodrum Peninsula

Bodrum Peninsula is located between Hellenic Trench in the west and Gökova Fault Zone in the east which is affected by hundreds of earthquakes every year. Because of its active environment is allowed to monitor tracers/precursors continuously to analyse natural processes. This study focused on the determination of ground water radon (²²²Rn) concentrations in the Bodrum Peninsula in terms of seismic activities. Radon levels of ten ground water wells were measured periodically throughout the peninsula and these wells were divided into two groups according to the number of earthquakes they are exposed. Radon variations in second group stations are fairly significant as a result of high number of earthquakes. In these stations, radon continuously increased before the seismic storm and then decreased step by step. The results indicated that radon variations in ground waters of Bodrum Peninsula can be a good indicator for seismic storms instead of one specific event.     

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).     

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.