Refined Locations of The Swarm Earthquakes In The Nový Kostel Focal Zone and Spatial Distribution of The January 1997 Swarm In Western Bohemia,Czech Republic     

Fischer  Tomáš  Horálek  Josef 《Studia Geophysica et Geodaetica》2000,44(2):210-226

In order to improve the accuracy of the spatial distribution of earthquake foci in the principal Novy Kostel focal zone, refined focal locations of about 1500 micro-earthquakes of the 1991 – 1997 period were determined using the relative Master-Event location method. To estimate the reduction in the scatter of located hypocentres, the results were compared with those obtained by routinely used FASTHYPO method and cluster analysis (the nearest-neighbour method) was applied to the located foci to evaluate the spatial distribution of the foci. Based on the results of refined location and of the cluster analysis, a concept of seismic energy release in space and time in the main focal zone was developed. Especially the January 1997 earthquake swarm was studied in detail: 946 events were located with the Master-Event location method, and the dimensions and geometry of focal clusters were determined. Type analysis was applied to waveforms to divide approximately 800 located events into eight multiplet groups to each of which a characteristic source mechanism was assigned. The spatial distribution of the foci as well as of the eight types of source mechanisms was revealed in this way and also the planes fitting the clusters of foci with two predominant source mechanisms were determined fairly well.  相似文献   

Synthetic gedrite: a stable phase in the system MgO-Al2O3-SiO2-H2O (MASH) at 800 °C and 10 kbar water pressure, and the influence of FeNaCa impurities     

H. Fischer  W. Schreyer  W. V. Maresch 《Contributions to Mineralogy and Petrology》1999,136(1-2):184-191

Seeded, solid-media piston-cylinder runs of unusually long duration up to 31 days indicate growth or persistence of synthetic gedrite of the composition □Mg₆Al[AlSi₇O₂₂](OH)₂(=6:1:7), prepared from the purest chemicals available, at 10 kbar water pressure and 800 °C. Conversely, breakdown was observed at 11 kbar and 850 °C to aluminous enstatite, Al₂SiO₅, and a melt of the composition MgO·Al₂O₃·8SiO₂. Thus, pure gedrite free of iron, sodium, and calcium is likely to have only a small PT stability field in the MASH system, estimated as 10 ± 1 kbar, 800 ± 20 °C, even though metastable growth of gedrite can be observed over a larger PT range. A second starting material with the anhydrous composition 5MgO · 2Al₂O₃ · 6SiO₂ also yielded gedrite of the composition 6:1:7, together with more aluminous phases such as kyanite, corundum or sapphirine, thus suggesting that the end-member gedrite defined as □Mg₅Al₂[Al₂Si₆O₂₂](OH)₂(=5:2:6) by the IMA Commission on New Minerals and Mineral Names probably does not exist. With the use of this second starting material, which contains FeNaCa impurities, growth of 6:1:7-gedrite was observed over a still wider PT-range. Seeded runs indicate that the true stability field of such slightly impure 6:1:7-gedrites may also be larger than that of the pure MASH phase and extend at least to 15 kbar, 800 °C. There is, thus, a remarkable stabilization effect on the orthoamphibole structure by impurities amounting only to a total of less than one weight percent of oxides in the starting material. The gedrites synthesized are structurally well ordered amphiboles nearly free of chain multiplicity faults, as revealed by HRTEM. The X-ray diffraction work on the gedrites synthesized yielded the smallest cell volume yet reported for this phase. The small stability field of the pure MASH gedrite is intersected by the upper pressure stability limit of hydrous cordierite for excess-H₂O conditions, thus leading to complicated phase relations for both gedrite and cordierite involving the additional phases aluminous enstatite, talc, quartz, Al₂SiO₅, melt and perhaps boron-free kornerupine. Received: 29 July 1998 / Accepted: 7 January 1999  相似文献   

Sulfur Hexafluoride and Potassium Bromide as Groundwater Tracers for Managed Aquifer Recharge     

Sarah P. Gerenday  Jordan F. Clark  Jeffrey Hansen  Ida Fischer  John Koreny 《Ground water》2020,58(5):777-787

Sulfur hexafluoride (SF₆) is an established tracer for use in managed aquifer recharge projects. SF₆ exsolves from groundwater when it encounters trapped air according to Henry's law. This results in its retardation relative to groundwater flow, which can help determine porous media saturation and flow dynamics. SF₆ and the conservative, nonpartitioning tracer, bromide (Br⁻ added as KBr), were introduced to recharge water infiltrated into stacked glacial aquifers in Thurston County, Washington, providing the opportunity to observe SF₆ partitioning. Br⁻, which is assumed to travel at the same velocity as the groundwater, precedes SF₆ at most monitoring wells (MWs). Average groundwater velocity in the unconfined aquifer in the study area ranges from 3.9 to 40 m/d, except in the southwestern corner where it is slower. SF₆ in the shallow aquifer exhibits an average retardation factor of 2.5 ± 3.8, suggesting an air-to-water ratio on the order of 10⁻³ to 10⁻² in the pore space. Notable differences in tracer arrival times at adjacent wells indicate very heterogeneous conductivity. One MW exhibits double peaks in concentrations of both tracers with different degrees of retardation for the first and second peaks. This suggests multiple flowpaths to the well with variable saturation. The confining layer between the upper two aquifers appears to allow intermittent connection between aquifers but serves as an aquitard in most areas. This study demonstrates the utility of SF₆ partitioning for evaluating hydrologic conditions at prospective recharge sites.  相似文献   

A new mathematical model of asymmetric hydraulic fracture growth          下载免费PDF全文

J. Mls  T. Fischer 《Geophysical Prospecting》2018,66(3):549-560

Hydraulic fractures generated by fluid injection in rock formations are often mapped by seismic monitoring. In many cases, the microseismicity is asymmetric relative to the injection well, which has been interpreted by stress gradient along the direction of the hydraulic fracture. We present a mathematical model of asymmetric hydrofracture growth based on relations between the solid‐phase stress and the fracture hydraulics. For single fracture and single injection point, the model has three parameters, hydraulic conductivities of the fracture wings, and normalised stress gradient and predicts the positions of the fracture tips as functions of time. The model is applied to a set of microseismic event locations that occurred during and after an injection process. Two different methods are suggested that make it possible to delineate the fracture tips from the set of microseismic events. This makes it possible to determine the model parameters and to check the agreement between the model prediction and the measured data. The comparison of the measured and modelled growth of fracture wings supports both the assumption of the non‐zero stress gradient and the existence of the post‐injection unilateral growth.  相似文献   

How well can we simulate complex hydro‐geomorphic process chains? The 2012 multi‐lake outburst flood in the Santa Cruz Valley (Cordillera Blanca,Perú)          下载免费PDF全文

Martin Mergili  Adam Emmer  Anna Juřicová  Alejo Cochachin  Jan‐Thomas Fischer  Christian Huggel  Shiva P. Pudasaini 《地球表面变化过程与地形》2018,43(7):1373-1389

Changing high‐mountain environments are characterized by destabilizing ice, rock or debris slopes connected to evolving glacial lakes. Such configurations may lead to potentially devastating sequences of mass movements (process chains or cascades). Computer simulations are supposed to assist in anticipating the possible consequences of such phenomena in order to reduce the losses. The present study explores the potential of the novel computational tool r.avaflow for simulating complex process chains. r.avaflow employs an enhanced version of the Pudasaini ( 2012 ) general two‐phase mass flow model, allowing consideration of the interactions between solid and fluid components of the flow. We back‐calculate an event that occurred in 2012 when a landslide from a moraine slope triggered a multi‐lake outburst flood in the Artizón and Santa Cruz valleys, Cordillera Blanca, Peru, involving four lakes and a substantial amount of entrained debris along the path. The documented and reconstructed flow patterns are reproduced in a largely satisfactory way in the sense of empirical adequacy. However, small variations in the uncertain parameters can fundamentally influence the behaviour of the process chain through threshold effects and positive feedbacks. Forward simulations of possible future cascading events will rely on more comprehensive case and parameter studies, but particularly on the development of appropriate strategies for decision‐making based on uncertain simulation results. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Validation of official erosion modelling based on high‐resolution radar rain data by aerial photo erosion classification          下载免费PDF全文

Franziska Katharina Fischer  Michael Kistler  Robert Brandhuber  Harald Maier  Melanie Treisch  Karl Auerswald 《地球表面变化过程与地形》2018,43(1):187-194

The universal soil loss equation (USLE) is the most frequently applied erosion prediction model and it is also implemented as an official decision‐making instrument for agricultural regulations. The USLE itself has been already validated using different approaches. Additional errors, however, arise from input data and interpolation procedures that become necessary for field‐specific predictions on a national scale for administrative purposes. In this study, predicted event soil loss using the official prediction system in Bavaria (Germany) was validated by comparison with aerial photo erosion classifications of 8100 fields. Values for the USLE factors were mainly taken from the official Bavarian high‐resolution (5 × 5 m²) erosion cadastre. As series of erosion events were examined, the cover and management factor was replaced by the soil loss ratio. The event erosivity factor was calculated from high‐resolution (1 × 1 km², 5 min), rain gauge‐adjusted radar rain data (RADOLAN). Aerial photo erosion interpretation worked sufficiently well and average erosion predictions and visual classifications correlated closely. This was also true for data broken down to individual factors and different crops. There was no reason to assume a general invalidity of the USLE and the official parametrization procedures. Event predictions mainly suffered from errors in the assumed crop stage period and tillage practices, which do not reflect interannual and farm‐specific variation. In addition, the resolution of radar data (1 km²) did not seem to be sufficient to predict short‐term erosion on individual fields given the strong spatial gradients within individual rains. The quality of the input data clearly determined prediction quality. Differences between USLE predictions and observations are most likely caused by parametrization weaknesses but not by a failure of the model itself. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Application of Large‐Scale Inversion Algorithms to Hydraulic Tomography in an Alluvial Aquifer          下载免费PDF全文

P. Fischer  A. Jardani  A. Soueid Ahmed  M. Abbas  X. Wang  H. Jourde  N. Lecoq 《Ground water》2017,55(2):208-218

Large‐scale inversion methods have been recently developed and permitted now to considerably reduce the computation time and memory needed for inversions of models with a large amount of parameters and data. In this work, we have applied a deterministic geostatistical inversion algorithm to a hydraulic tomography investigation conducted in an experimental field site situated within an alluvial aquifer in Southern France. This application aims to achieve a 2‐D large‐scale modeling of the spatial transmissivity distribution of the site. The inversion algorithm uses a quasi‐Newton iterative process based on a Bayesian approach. We compared the results obtained by using three different methodologies for sensitivity analysis: an adjoint‐state method, a finite‐difference method, and a principal component geostatistical approach (PCGA). The PCGA is a large‐scale adapted method which was developed for inversions with a large number of parameters by using an approximation of the covariance matrix, and by avoiding the calculation of the full Jacobian sensitivity matrix. We reconstructed high‐resolution transmissivity fields (composed of up to 25,600 cells) which generated good correlations between the measured and computed hydraulic heads. In particular, we show that, by combining the PCGA inversion method and the hydraulic tomography method, we are able to substantially reduce the computation time of the inversions, while still producing high‐quality inversion results as those obtained from the other sensitivity analysis methodologies.  相似文献