Comparison of 2D debris-flow simulation models with field events

Three two-dimensional (2D) debris-flow simulation models are applied to two large well-documented debris-flow events which caused major deposition of solid material on the fan. The models are based on a Voellmy fluid rheology reflecting turbulent-like and basal frictional stresses, a quadratic rheologic formulation including Bingham, collisional and turbulent stresses, and a Herschel–Bulkley rheology representing a viscoplastic fluid. The rheologic or friction parameters of the models are either assumed a priori or adjusted to best match field observations. All three models are capable of reasonably reproducing the depositional pattern on the alluvial fan after the models have been calibrated using historical data from the torrent. Accurate representation of the channel and fan topography is especially important to achieve a good replication of the observed deposition pattern.     

Test of sediment initial-motion theories using irregular-wave field data

Sediment initial-motion theories predict the flow conditions that coincide with onset of sediment motion, but usually the most that can be determined from burst-sampled field data is whether or not sediment was in motion. Furthermore, initial-motion theories are usually based on regular-wave laboratory data, with little or no guidance given on how such theories are to be transferred to the real world of irregular waves. A field dataset obtained from the zone of wave shoaling beyond the surfzone is used to compare the performance of three initial-motion theories in a way that takes explicit account of wave irregularity and the limitations of burst sampling. The dataset comprises video images of the seabed and measurements of waves, currents and suspended sediment. The initial-motion theories tested were Komar & Miller's (1975 , J. Sedim. Petrol ., 45, 362–367) 'wave-orbital-speed' theory, a 'wave-stress' theory, and a 'wave-plus-current-stress' theory. Fourteen transitions from no sediment motion to sediment motion were observed, but not all of those represented a challenging test of theory. Using the criterion that the best theory is the one that minimizes errors in classifying bursts as 'no sediment motion' or 'sediment in motion', Komar & Miller's (1975 ) theory was found to perform the best when waves were characterized by significant wave height and mean spectral period, both of which can be estimated directly from pressure data alone. Komar and Miller's theory was better at predicting the onset of extended transport events, which occurred during confused seas, rather than the transition back to moribund seabed under clean swell at the end of such events. The conclusion regarding best theory is dependent on the choice of scales used to characterize wave motion. The way forward therefore is to standardize and define terms precisely.     

Investigating 2-D MT inversion codes using real field data

There are currently a significant number of two-dimensional (2-D) and three-dimensional (3-D) inversion codes available for magnetotelluric (MT) data. Through various 2-D inversion algorithms suggested so far, the classical Occam's inversion, the data space Occam's inversion, the nonlinear conjugate gradient (NLCG) method, and the Gauss–Newton (GN) method are fundamental driving methods to find optimum earth models, and OCCAM, DASOCC, NLCG, and MT2DInvMatlab are possible candidates one can find in the public domain that implement these algorithms for 2-D MT inversions, respectively. In this study, we investigate the pros and cons (strength and weakness) of these codes to help one use them efficiently in practical works and, as an introductory guide, further develop (sophisticate or extend) them, especially for the 3-D case. To achieve this goal, we applied each one of the four aforementioned codes on a profile of real MT field dataset. Then, further investigations have been done by performing several inversion tests to see how each code can find the appropriate model to reconstruct the subsurface resistivity structure. Numerical experiments show that the two parameters, regularization and target misfit, in addition to the main criteria of inversion (such as the forward and the sensitivities calculation method, and the type of inversion algorithm), are very important to produce the expected model in inversion. The regularization parameter that acts to trade off between model norm and data misfit can affect the inversion process in terms of both the computational efficiency and the accuracy of the obtained model. Also, lack of insufficient precision to choose the target misfit can lead the inversion to produce and reach an incorrect model.     

External field characterization using CHAMP satellite data for induction studies

Knowledge of external inducing source field morphology is essential for precise estimation of electromagnetic (EM) induction response. A better characterization of the external source field of magnetospheric origin can be achieved by decomposing it into outer and inner magnetospheric contributions, which are best represented in Geocentric Solar Magnetospheric (GSM) and Solar Magnetic (SM) reference frames, respectively. Thus we propose a spherical harmonic (SH) model to estimate the outer magnetospheric contribution, following the iterative reweighted least squares approach, using the vector magnetic data of the CHAMP satellite. The data covers almost a complete solar cycle from July 2001 to September 2010, spanning 54,474 orbits. The SH model, developed using orbit-averaged vector magnetic data, reveals the existence of a stable outer magnetospheric contribution of about 7.39 nT. This stable field was removed from the CHAMP data after transforming to SM frame. The residual field in the SM frame acts as a primary source for induction in the Earth. The analysis of this time-series using wavelet transformation showed a dominant 27-day periodicity of the geomagnetic field. Therefore, we calculated the inductive EM C-response function in a least squares sense considering the 27-day period variation as the inducing signal. From the estimated C-response, we have determined that the global depth to the perfect substitute conductor is about 1132 km and its conductivity is around 1.05 S/m.     

冀西北地区泥石流发育的环境因素遥感研究

文章介绍了利用Landsat—TM遥感图像对影响泥石流发育的环境因素所作的定量研究。该项研究以在冀西北1．8万km^2范围内解译出的339条(处)泥石流沟作为研究对象，在全面分析了该区影响泥石流发育的环境因素后，选择出植被盖度、岩石类别、沟床坡降、流域平面形态、地形地貌特征等5项因素，通过提取遥感图像特征进行分级细化和定量研究。采取大样本统计方法，得出每种因素在不同状态下与泥石流发育的关系，定量表示不同发育状态的环境因素对泥石流发育的影响。文章还对影响泥石流发育的所有环境因素进行了分类和评价，将9类因素归结为影响泥石流发育的物源因素和影响泥石流运动状态的因素2大类，建立了泥石流发育影响因素分类体系，并评价、排序了它们在泥石流孕育过程中的重要性。最后，总结出研究区最易发生泥石流的环境因素组合。     

瞬变电磁法感应电压场与B场探测效果的数值计算对比分析

本文通过一维和三维正演程序分别生成了回线源瞬变电磁法的感应电压场和B z场数据,并从多个角度对比了二者的探测效果。通过多个模型对比分析了这两种数据在当前主流硬件的数据采集精度下的最长有效延迟时间;通过全时视电导率计算与一维反演对比分析了两种数据的纵向分辨率和横向分辨率。结果表明,在本文采用的仪器精度水平和测量方式下,只有当模型中存在电导率≥0.036 S/m的高导异常体时,B z场的有效观测延迟时间才可能比感应电压场更长;B z场相比感应电压场虽然能够提前感知到地下异常体,但是在横向和纵向分辨率以及对异常体电导率的呈现程度上均比感应电压场差。在实际野外测量时,不建议仅开展B z场测量,而是在有条件情况下,同时采集感应电压场和B z场,充分利用感应电压场和B z场各自的优势,达到最佳的探测效果。     

Landslide and debris-flow hazard analysis and prediction using GIS in Minamata–Hougawachi area, Japan

On July 20, 2003, following a short duration of heavy rainfall, a debris-flow disaster occurred in the Minamata–Hougawachi area, Kumamoto Prefecture, Japan. This disaster was triggered by a landslide. In order to assess the landslide and debris-flow hazard potential of this mountainous region, the study of historic landslides is critical. The objective of the study is to couple 3D slope-stability analysis models and 2D numerical simulation of debris flow within a geographical information systems in order to identity the potential landslide-hazard area. Based on field observations, the failure mechanism of the past landslide is analyzed and the mechanical parameters for 3D slope-stability analysis are calculated from the historic landslide. Then, to locate potential new landslides, the studied area is divided into slope units. Based on 3D slope-stability analysis models and on Monte Carlo simulation, the spots of potential landslides are identified. Finally, we propose a depth-averaged 2D numerical model, in which the debris and water mixture is assumed to be a uniform continuous, incompressible, unsteady Newtonian fluid. The method accurately models the historic debris flow. According to the 2D numerical simulation, the results of the debris-flow model, including the potentially inundated areas, are analyzed, and potentially affected houses, river and road are mapped.     

泥石流堆积物的结构维数及其地质意义

研究表明,泥石流堆积物的粒度组成具有分形特征.一般,取Mr为粒径小于r的颗粒含量,据之计算泥石流堆积物的结构维数.这种计算方法忽略了能够反映泥石流动力特征的粗大颗粒,而且不便于现场实施.本文把M定义为粒径大于r的颗粒含量,不仅突出了粗大颗粒的特征,而且便于现场实施.与一般方法相反,新方法所得泥石流粒度分维曲线倾向r轴正向,与粒度轴具有唯一的交点,该交点所表示的粒度反映了泥石流所能携带的最大块度,据之可对该地区泥石流的运动速度及对建筑物的冲击力作出估计.     

Computing the 3D in-situ stress field from shut-in pressure data using statistical regression

The paper describes a multivariable statistical regression technique for computing the 3D stress tensor applied to the shut-in pressure data obtained on fractures during in-situ stress measurement by hydraulic fracturing in a short borehole. This method computes the mean value of components of the 3D stress tensor and their confidence intervals at a desired confidence level. This has been applied to the data of shut-in pressure from Narwapahar mine, India and Kamaishi mine, Japan. The computed in-situ stress tensor is corroborated with that obtained by other methods.     

用静力触探资料估算单桩竖向极限承载力标准值的几点体会

本文通过实例,用静力触探资料进行了单桩竖向极限承载力标准值的估算,并把估算结果和传统的经验参数法估算结果进行了对比,同时,又用单桩静力载荷试验资料进行了验证,从而说明该方法在不断积累经验后,在本地区是可以推广应用的。     

Estimation and analysis of the surface velocity field of mountain glaciers in Muztag Ata using satellite SAR data

Muztag Ata is a mountain known as the “Father of glaciers” in the west of China. However, its glacier flow pattern has never been studied. In this paper, the velocity of mountain glaciers on Muztag Ata is mapped by two methods (InSAR and offset-tacking) using SAR data. This map provides a detailed view of the features of glacier motion on Muztag Ata. A special effort was also made to assess the accuracy of the glacier velocity estimates. To ensure the accuracy of the derived results, the validation of the results was conducted over two glaciers (Saliymek Glacier and Kuksay Glacier). The two methods yielded similar results that agree well with each other. The patterns of glacier velocity on Muztag Ata suggest that mountain topography, westerly winds and the monsoon have a strong influence. Our results show that motion of glaciers in the southern and western regions of Muztag Ata is faster than that in the northern and eastern regions. Eleven glaciers were identified, along which glacier velocities exhibited distinctive behavior in terms of the spatial variability of the glacier motion. The occurrence of the local flow maxima and minima at consistent locations over different parts of different glaciers suggests that the subglacial topography, glacier size and glacier orientation affect the overall flow patterns. The velocities are very low in the surface debris cover of some glaciers, which suggests debris cover has an impact on glacier motion.     

Comparison of debris-flow volumes from burned and unburned areas

The goals of this work are to show the range of debris-flow volumes and watershed characteristics for several locations, and the differences in flow volumes for events triggered soon after wildfire. A dataset of 929 events was divided into groups based on location and burn status. The three unburned locations show significant differences: debris flows from the Italian Alps are larger and generate more debris per unit basin area or unit channel length than flows in the Western USA or in the Pacific Northwest. However, some of the observed differences may be attributed to the skew of the Italian Alps dataset towards larger events, and the small size and limited range of the Pacific Northwest data. For burned watersheds in the Western U.S. events, there is a clear progression in decreasing volume in debris flows as basins recover from the wildfire: it takes approximately 1 year, or at a few locations, as much as 3 years, for debris production to return to pre-fire rates. The difference is most apparent when the data are normalized for basin area (the area yield, which is 2× larger for burned basins) or for channel length (the length yield, which is 1.6× larger for burned basins). When normalized simultaneously for basin area, channel length, and channel gradient, burned areas produce significantly more debris (2.7–5.4 times as much). Burned areas in the Western USA are more sensitive to wildfire and produce larger debris flows than burned areas in more humid climates such as the Pacific Northwest.     

Variability of photosynthetic pigments in the Colombian Pacific Ocean and its relationship with the wind field using ADEOS-I data

Variability of the oceanographic conditions in the Colombian Pacific Ocean, a part of the Panama Basin, is subjected to the variability of wind conditions in the equatorial part of the Pacific Ocean. Data of OCTS and NSCAT of ADEOS-I satellite provided as monthly averages for the period November 1996-June 1997 by NASDA, were processed and manipulated. A meridional (N-S) component and a zonal (E-W) component were run in order to analyse the data variability and correlation. It is concluded that the variability of the oceanic surface chlorophyll and SST in the Colombian Pacific is a seasonal event related to the migration of the ITCZ and the generation of a wind jet at the Isthmus of Panama. Upwelling due to the wind rotor is present throughout the whole period, with variable spatial distribution and a tendency to be located towards the eastern part of the basin. In a similar way, high chlorophyll concentrations observed in March coincide with both the intensification of the vertical velocities during that month, and the maximal rise of the thermocline in the northern part of the Panama Basin. Picture series of surface chlorophyll, SST, wind stress and Ekman pumping are provided for the studied area.     

滑坡泥石流风险评估框架体系

滑坡泥石流灾害风险评估目前没有一个统一的概念体系和理论框架.从滑坡泥石流风险评估的基本概念出发,综合分析不确定性与灾害以及灾害与风险之间的关系,明确区分了“灾害体”、“灾害事件”和“灾害现象”三种含义,界定了灾害易发性、危险性和风险性的内涵.然后从这些明确的概念出发,提出了危险性和易损性的数学表达形式,由此构建了滑坡泥石流风险评估的理论框架,以期能够为今后的滑坡泥石流风险研究工作提供参考.     

Inversion of potential field data

The problem of inversion of potential field data is a challenging one because of the difficulty in obtaining a unique solution. This paper identifies various types of nonuniqueness and argues that it is neither possible nor necessary to remove all categories of nonuniqueness. Some types of nonuniqueness are due to human limitations and choice and these would always persist. Listing all the solutions, imposing additional constraints on the acceptable solutions, a priori idealization, use of a priori or supplementary information, characterizing what is common to all the solutions, obtaining extremal solutions, seeking a distribution of all possible solutions, etc. are various responses in the face of nonuniqueness. It is shown that merely the form of nonuniqueness is changed by all these techniques. Some algorithms, which should be used to obtain the global minimum of the objective function are discussed. The conceptual commonality underlying seemingly different approaches and the possibility of nonunique interpretations of the same numerical results due to different axiomatic contexts are both elucidated.     

Gravity field recovery from airborne gradiometer data using collaction and taking into account correlated errors

Least squares collocation is a very comprehensive method for gravity field modelling, since it may use known noise characteristics of the data. In many earlier applications the errors affecting the data were considered uncorrelated, mainly due to the difficulty in estimating the systematic character of such kind of errors. In this study, error covariance functions of airborne gravity gradiometer data are estimated by comparing model covariance functions with empirical covariance functions of the gravity gradiometer data. The model covariance functions were estimated from accurate surface gravity data and continuated upward to the height of the airborne measurements using the covariance propagation law. The estimated error covariance functions were modeled as finite ones and used as an additional information for the prediction of gravity anomalies from gravity gradiometer data. The assessment of the prediction results was made by comparing the gravity values predicted from the airborne gradient data and showed up to 25% improvement compared to not using correlated errors.     

Quantifying a critical marl thickness for vertical fracture extension using field data and numerical experiments

In fractured reservoirs characterized by low matrix permeability,fracture networks control the main fluid flow paths.However,in layered reservoirs,the vertical extension of fractures is often restricted to single layers.In this study,we explored the effect of changing marl/shale thickness on fracture extension using comprehensive field data and numerical modeling.The field data were sampled from coastal exposures of Liassic limestone-marl/shale alternations in Wales and Somerset(Bristol Channel Basin,UK).The vertical fracture traces of more than 4000 fractures were mapped in detail.Six sections were selected to represent a variety of layer thicknesses.Besides the field data also thin sections were analyzed.Numerical models of fracture extension in a two-layer limestone-marl system were based on field data and laboratory measurements of Young's moduli.The modeled principal stress magnitude σ_3 along the lithological contact was used as an indication for fracture extension through marls.Field data exhibit good correlation(R~2=0.76) between fracture extension and marl thickness,the thicker the marl layer the fewer fractures propagate through.The model results show that almost no tensile stress reaches the top of the marl layer when the marls are thicker than 30 cm.For marls that are less than 20 cm,the propagation of stress is more dependent on the stiffness of the marls.The higher the contrast between limestone and marl stiffness the lower the stress that is transmitted into the marl layer.In both model experiments and field data the critical marl thickness for fracture extension is ca.15-20 cm.This quantification of critical marl thicknesses can be used to improve predictions of fracture networks and permeability in layered rocks.Up-or downsampling methods often ignore spatially continuous impermeable layers with thicknesses that are under the detection limit of seismic data.However,ignoring these layers can lead to overestimates of the overall permeability.Therefore,the understanding of how fractures propagate and terminate through impermeable layers will help to improve the characterization of conventional reservoirs.     

Estimate of heat flux at the ice-water interface in Lake Baikal from experimental data

An original system for measuring temperature in the ice cover and subglacial water and an increase in the ice thickness provides data necessary for calculation of the heat flux at the ice-water interface. Successive freezing of 1-mm temperature sensors during the ice growth allows us to measure temperature gradients in the vicinities of the ice-water interface for the first time. An analytical equation derived from the Stefan condition allows calculations of the heat flux at the phase boundary on the basis of the experimental data, which agree with independent estimates that have been made on the basis of the subglacial temperature gradients and are within the 4–39 W/m² range. The flow at the ice-water interface is comparable with the heat flux inside the ice depth and significantly affects the dynamics of the ice cover thickness.     

Impact of industrial effluents on groundwater around Pali city, Rajasthan using field and satellite data

Groundwater pollution due to industrial effluents from textile units around Pali city area is the major concern to the local villagers and the district administration. Indiscriminate discharge of these effluents in the past two decades caused severe damage to the agricultural land and groundwater resources within 3 km buffer zone of the Bandi river. Remote Sensing and GIS techniques are found to be better tools in assessing the damage in agricultural crops during 1997 and 2006 with the help of high resolution satellite images. Groundwater fluctuation trend with annual rainfall pattern during 1985 and 2005 indicate good recharge in the study area. Detailed analysis of groundwater quality parameters (TDS, Cl and SO₄) and heavy metals (Cu, Pb, Zn, Fe, Cd and Cr) for 1997–98 indicates maximum concentration around Chatelao village and Dholera Jagir in the downstream direction of Bandi river. However, temporal analysis of groundwater samples collected in January, 2009 shows marginal decrease in concentration of TDS, Cl, SO₄, Pb and Cu in both groundwater as well as river effluents. Slight improvement in water quality especially heavy metals in the last 12 years (1998–2009) may be attributed to the appropriate measures (treatment of wastewater and solid waste disposal) taken by the establishment of three Common Effluent Treatment Plants (CETP) in Pali city area. However, a few stringent actions may be taken to avoid direct discharge of the effluents into Bandi river.     

2D inversion of the magnetotelluric data from Mahallat geothermal field in Iran using finite element approach

The natural-field magnetotelluric (MT) method has proven very useful for mapping the geothermal fields as resistivity sections. The depth of investigation of the MT method is sufficiently large to penetrate deep into the upper crust. MT soundings along two transects across Mahallat geothermal field in Iran were carried out to determine the crustal structure in the region. The selected MT profiles in the region cross over the hydrothermally altered zones and different geological structures. Data were acquired along two profiles crossing the Mahallat hot springs with a total of 28 MT stations in a frequency range of 8,000 to 0.008 Hz. Spacing between stations was kept 500 m for a good resolution. We have used the code MT2DInvMATLAB for inversion using the method of finite elements for forward modeling. Apparent resistivity and phase data of transverse electric (TE), transverse magnetic (TM), and TE + TM modes along each profile were modeled. The geothermal fluid reservoir is resolved at 1,000 to 3,000 m depth and the geothermal resource is estimated to be located at 7,000 m or deeper.