SH-waves scattering from a partially filled semi-circular alluvial valley

A series solution of the plane SH-waves incident on a partially filled semi-circular alluvial valley imbedded in a half-space is presented. Based on the region-matching method, the analysed region is decomposed into two subregions by the interface between two media. The antiplane displacement field of each subregion is expressed in terms of an infinite series of cylindrical wavefunctions with unknown expansion coefficients. After imposing the traction-free condition on the curved valley surface and the matching conditions on the interface with the aid of Graf's addition theorem, the unknown coefficients are obtained. Both the frequency- and time-domain responses are evaluated. In the theoretical derivation of this work, two classical exact series solutions are also included, so the present series solution is more general than those given before. Visible effects of different physical parameters on ground surface motions are illustrated in graphical form.     

Jutulhogget — canyon og refugium

Aas, B. 1970. Jutulhogget, canyon and refuge. Norsk geogr. Tidsskr. 24, 59-81.

Jutulhogget is a big canyon in northern Hedmark, cut down by water from an ice-dammed lake in Österdalen flowing over the mountain ridge east of Barkald into Tylldal. In this canyon vigorous elms (Ulmus glabra) occur in three neighbouring localities. The upper parts of the screes on the steep south-facing side of the canyon nourish a rich and varied flora. The south-exposed screes with good light conditions, are thermally favoured, and soil and water conditions are suitable The elm trees and also several thermophilous herbs, rare elsewhere in the northern part of Österdalen, must be relicts from the Post-glacial warm period. Jutulhogget is a preserve.     

20世纪末的一次重大地理发现──雅鲁藏布江大峡谷为世界之最的论证

雅鲁藏布江下游围绕喜马拉雅山东端最高峰南迦巴瓦峰（７７８２ｍ）作奇特的马蹄形大拐弯，连续的深切割在青藏高原东南斜面上，长达４９６．３ｋｍ，最深达５３８２ｍ，是世界上最大的峡谷。它的论证和被发现，是２０世纪末一次重大的地理发现。大峡谷是适应板块缝合构造带发育的构造谷，它还是南来水汽进入青藏高原的最大通道，它所造就的独特自然环境和地理景观，以及以生物和水力为主的丰富自然资源，是人类共同的财富。进行世界最大峡谷的地学、生物学理论与应用的系统研究，对大峡谷的开发、规划、永续利用提供科学依据，建立大峡谷自然保护区是当务之急。     

20世纪末的一次重大地理发现──雅鲁藏布江大峡谷为世界之最的论证

雅鲁藏布江下游围绕喜马拉雅山东端最高峰南迦巴瓦峰(7782m)作奇特的马蹄形大拐弯,连续的深切割在青藏高原东南斜面上,长达496.3km,最深达5382m,是世界上最大的峡谷。它的论证和被发现,是20世纪末一次重大的地理发现。大峡谷是适应板块缝合构造带发育的构造谷,它还是南来水汽进入青藏高原的最大通道,它所造就的独特自然环境和地理景观,以及以生物和水力为主的丰富自然资源,是人类共同的财富。进行世界最大峡谷的地学、生物学理论与应用的系统研究,对大峡谷的开发、规划、永续利用提供科学依据,建立大峡谷自然保护区是当务之急。     

Outflow of Pacific water from the Chukchi Sea to the Arctic Ocean

Pacific water exits the Chukchi Sea shelf through Barrow Canyon in the east and Herald Canyon in the west,forming an eastward-directed shelfbreak boundary current that flows into the Beaufort Sea.Here we summarize the transformation that the Pacific water undergoes in the two canyons,and describe the characteristics and variability of the resulting sbelfbreak jet,using recently collected summertime hydrographic data and a year-long mooring data set.In both canyons the northward-flowing Pacific winter water switches from the western to the eastern flank of the canyon,interacting with the northward-flowing summer water.In Barrow canyon the vorticity structure of the current is altered,while in Herald canyon a new water mass mode is created.In both instances hydraulic effects are believed to be partly responsible for the observed changes.The shelfbreak jet that forms from the canyon outflows has distinct seasonal configurations,from a bottom-intensified flow carrying cold,dense Pacific water in spring,to a surface-intensified current advecting warm,buoyant water in summer.The current also varies significantly on short timescales,from less than a day to a week.In fall and winter much of this mesoscale variability is driven by storm events,whose easterly winds reverse the current and cause upwelling.Different types of eddies are spawned from the current,which are characterized here using hydrographic and satellite data.     

Morphotectonics and incision of the Kaoping submarine canyon, SW Taiwan orogenic wedge

The Kaoping submarine canyon developed on the frontal orogenic wedge off SW Taiwan and is the largest one among others. The canyon begins at the mouth of the Kaoping River, crosses the narrow shelf and broad slope region, and finally merges into the northern Manila Trench for a distance of about 260 km. Using reflection seismic sections and bathymetric mapping this paper reveals the geomorphic characteristics of the Kaoping Canyon strongly related to structural and sedimentary processes. The combined morphometry statistics analysis, seismic interpretations of structures and examinations of detailed bathymetric charts indicate that regional canyon morphology is strongly linked to intrusions of mud diapirs in the upper reach of the canyon and thrust faulting in the middle and lower reaches which produce two prominent morphological breaks of the course of the Kaoping Canyon with two sharp bends. Although excavation of floor and enlargement of the Kaoping Canyon are mainly attributed to downslope erosion of seabed, incision of this canyon is also strongly complicated by mud diapiric intrusions (upper reach), westward thrust faults (middle reach), and regional base level tilting (lower reach). The resultant cross-sectional morphology along the Kaoping Canyon changes considerably, ranging from U-shaped, broad V-shaped, to irregular troughs. The Kaoping Canyon may be served as a variant of canyon model of active margins with a distinct morphology of two sharp bends along the canyon course associated with structure deformation.     

青藏高原东部样带农牧民生计脆弱性评估

脆弱性评估为脆弱性地区农户摆脱贫困、区域可持续发展提供科学依据。以青藏高原东部样带为例,基于可持续生计框架,建立了农牧民生计脆弱性评估的指标体系,利用11个乡镇的879户农牧民样本数据,开展了不同地带生计脆弱性评估。该指标体系反映了农牧民面临的主要风险,其生计资产,以及农牧民和政府应对风险的措施。结果表明:高原区农牧民生计脆弱性程度高于山原区和高山峡谷区。高原区的满掌乡最为脆弱,即便有政府的帮助,农牧民也不能应对风险。脆弱性程度高的山原区上部和高原区,处于不能适应的边缘,如不采取措施,当地牧民将不能应对气候变化、草地退化、药材退化等多种风险。导致该区牧民生计脆弱的原因既有各种风险的冲击,也因牧民自身生计资产和适应能力的不足。高山峡谷区和山原区下部的乡镇,农牧民能有效地应对风险,需进一步拓宽第二、第三产业就业渠道。因此,高原区和山原区上部的纯牧区是脆弱区域,政府应采取积极的措施,增强农牧民的适应能力。政府的救助措施应从改善自然资产转变到改善人力资产和金融资产,如技能培训、实行医保和畜病防治全覆盖、提供低息和无息贷款、在黑土滩区全面实行退牧还草、对退化草场进行治理和恢复。     

Synthetic logs of multipole sources in boreholes based on the Kelvin–Voigt stress–strain relation

We design a numerical algorithm for wave simulation in a borehole due to multipole sources. The stress–strain relation of the formation is based on the Kelvin–Voigt mechanical model to describe the attenuation. The modelling, which requires two anelastic parameters and twice the spatial derivatives of the lossless case, simulates 3-D waves in an axisymmetric medium by using the Fourier and Chebyshev methods to compute the spatial derivatives along the vertical and horizontal directions, respectively. Instabilities of the Chebyshev differential operator due to the implementation of the fluid–solid boundary conditions are solved with a characteristic approach, where the characteristic variables are evaluated at the source central frequency. The algorithm uses two meshes to model the fluid and the solid. The presence of the logging tool is modelled by imposing rigid boundary conditions at the inner surface of the fluid mesh. Examples illustrating the propagation of waves are presented, namely, by using monopoles, dipoles and a quadrupoles as sources in hard and soft formations. Moreover, the presence of casing and layers is considered. The modelling correctly simulates the features—traveltime and attenuation—of the wave modes observed in sonic logs, namely, the P and S body waves, the Stoneley wave, and the dispersive S waves in the case of multipole sources.     

Implementation of perfectly matched layers in an arbitrary geometrical boundary for elastic wave modelling

The perfectly matched layer (PML) absorbing boundary condition is incorporated into an irregular-grid elastic-wave modelling scheme, thus resulting in an irregular-grid PML method. We develop the irregular-grid PML method using the local coordinate system based PML splitting equations and integral formulation of the PML equations. The irregular-grid PML method is implemented under a discretization of triangular grid cells, which has the ability to absorb incident waves in arbitrary directions. This allows the PML absorbing layer to be imposed along arbitrary geometrical boundaries. As a result, the computational domain can be constructed with smaller nodes, for instance, to represent the 2-D half-space by a semi-circle rather than a rectangle. By using a smooth artificial boundary, the irregular-grid PML method can also avoid the special treatments to the corners, which lead to complex computer implementations in the conventional PML method. We implement the irregular-grid PML method in both 2-D elastic isotropic and anisotropic media. The numerical simulations of a VTI lamb's problem, wave propagation in an isotropic elastic medium with curved surface and in a TTI medium demonstrate the good behaviour of the irregular-grid PML method.     

CANYON GEOMETRY,THE URBAN FABRIC AND NOCTURNAL COOLING: A SIMULATION APPROACH

A simulation model for surface cooling in urban street canyons under calm conditions is described, based upon a simplified energy budget for the canyon facets containing only the net longwave and substrate heat flux densities. The former term is evaluated from the canyon radiation budget model of Arnfield (1976), the latter by numerically approximating the Fourier heat conduction equation. Equilibrium temperatures evolve through the nocturnal period for specified canyon and incoming longwave irradiance characteristics. Numerical experiments conducted with the model show that canyon geometry alone exerts a significant effect on cooling rates and, hence, on heat island intensity. Construction materials and internal building climate control tend to enhance spatial variations in nocturnal temperatures. The effects of wall thickness, sky radiance distribution and cloud cover also are investigated. Results show qualitative and quantitative correspondences with previous field and scale-model studies. Sources of error and desirable model refinements are discussed. [Key words: urban climatology, heat island, heat flux, nocturnal cooling, simulation model.]     

A new nutation series for a more realistic model earth

The frequency-dependent correction coefficients with respect to the forced nutations of a rigid earth are computed using the complex scalar gravitational-motion equations for an earth model with an anelastic mantle. Oceanic loads and tidal currents enter the model via outer boundary conditions. The ellipticity of the core-mantle boundary and the dynamical ellipticity are adjusted to observations. This requires the behaviour inside the model earth to be regarded as non-hydrostatic. Some relevant equations for the evaluation of boundary conditions and some terms in the equations of motion are expanded to second order in ellipticity. The computation of the equipotential-surface ellipticity profile is carried to second order as well. These second-order expansions lead to increased accuracy of the results in general. Moreover, one achieves a better reliability for the integration at frequencies close to a resonance. This allows the integration of the equations of motion at any relevant nutation period without the need for a normal-mode expansion. A complete new nutation series for a realistic model earth is presented.     

A 2-D spectral-element method for computing spherical-earth seismograms—II. Waves in solid–fluid media

We portray a dedicated spectral-element method to solve the elastodynamic wave equation upon spherically symmetric earth models at the expense of a 2-D domain. Using this method, 3-D wavefields of arbitrary resolution may be computed to obtain Fréchet sensitivity kernels, especially for diffracted arrivals. The meshing process is presented for varying frequencies in terms of its efficiency as measured by the total number of elements, their spacing variations and stability criteria. We assess the mesh quantitatively by defining these numerical parameters in a general non-dimensionalized form such that comparisons to other grid-based methods are straightforward. Efficient-mesh generation for the PREM example and a minimum-messaging domain decomposition and parallelization strategy lay foundations for waveforms up to frequencies of 1 Hz on moderate PC clusters. The discretization of fluid, solid and respective boundary regions is similar to previous spectral-element implementations, save for a fluid potential formulation that incorporates the density, thereby yielding identical boundary terms on fluid and solid sides. We compare the second-order Newmark time extrapolation scheme with a newly implemented fourth-order symplectic scheme and argue in favour of the latter in cases of propagation over many wavelengths due to drastic accuracy improvements. Various validation examples such as full moment-tensor seismograms, wavefield snapshots, and energy conservation illustrate the favourable behaviour and potential of the method.     

VALIDATION OF AN ESTIMATION MODEL FOR URBAN SURFACE ALBEDO

The albedo measurements of Aida (1982), made over simulated urban surfaces constructed from arrangements of concrete blocks into canyon and grid configurations, are used to evaluate the performance of the urban canyon radiation model of Arnfield (1976a, 1982). The model is shown to be capable of producing acceptable estimates of surface albedo for city land-use zones consisting predominantly of canyons with lengths considerably greater than their width, especially for high sun (high irradiance) conditions. For the data best suited to model validation, about half the albedos were estimated to within ±5% and all were within ±10%. For grid canyon configurations, the method yields less satisfactory results but it is argued that errors will be less significant for surface geometries more realistic than those employed by Aida which possessed very short block lengths in relation to street widths. [Key words: urban climate, energy-budget climatology, albedo, radiation model.]     

云贵高原区南昆铁路沿线溶洞发育规律

云贵高原可分为高原面、阶状河谷和深切峡谷三种地貌区,基于对南昆铁路沿线的调查,总结各区的溶洞发育规律与铁路定线原则。     

生态地理区域界线划分的指标体系

生态地理区域界线由一系列反映生态地理区域特征的指标为依据 ,通过其空间差异落实到具体的空间位置上。客观地认识和划定生态地理区域界线是揭示生态环境时空有序性的重要途径 ,是地域系统研究的基础。生态地理区域界线是两个相邻的、彼此不同的生态地理区质上转变的线或带 ,反映同一等级内划分出来的内部相对一致性与外部的差异性。界线代表有一定宽度的带 ,而且可能随着时间而迁移变化 ,等级越低界线越明显 ,等级越高界线越宽。在生态地理区域划分中 ,先选择人力不能大规模改变的几个主要因素 :温度指标 ,主要指标是日平均气温≥ 1 0℃的天数和积温 ,最冷月平均气温 ,最暖月平均气温等 ;水分指标 ,干湿指数 ,目前比较普遍采用的是年干燥度 ,它可以近似地表征某一地方的干湿程度 ;年降水量的资料通常比较可靠 ,但潜在蒸发的计算需要改进和提高。生态地理区域较高级单位的划分依据侧重考虑生物气候的差异 ,先注意水平地带性 ,由于气候台站的有限性 ,所划分出的界线往往用植被界线去修正 ;而垂直地带性则将潜在植被与气候联系起来 ,按照降水量、潜在蒸发率和生物温度来进行划分。如何处理级别与依据和指标之间的关系是另一个重要问题 ,在这个问题的处理上 ,国内外很不统一。     

Eco-environment range in the source regions of the Yangtze and Yellow rivers

Based on geographical and hydrological extents delimited, four principles are identified, as the bases for delineating the ranges of the source regions of the Yangtze and Yellow rivers in the paper. According to the comprehensive analysis of topographical characteristics, climate conditions, vegetation distribution and hydrological features, the source region ranges for eco-environmental study are defined. The eastern boundary point is Dari hydrological station in the upper reach of the Yellow River. The watershed above Dari hydrological station is the source region of the Yellow River which drains an area of 4.49×104 km2. Natural environment is characterized by the major topographical types of plateau lakes and marshland, gentle landforms, alpine cold semi-arid climate, and steppe and meadow vegetation in the source region of the Yellow River. The eastern boundary point is the convergent site of the Nieqiaqu and the Tongtian River in the upstream of the Yangtze River. The watershed above the convergent site is the source region of the Yangtze River, with a watershed area of 12.24×104 km2. Hills and alpine plain topography, gentle terrain, alpine cold arid and semi-arid climate, and alpine cold grassland and meadow are natural conditions in the source region of the Yangtze River.     

Headless submarine canyons and fluid flow on the toe of the Cascadia accretionary complex

Headless submarine canyons with steep headwalls and shallowly sloping floors occur on both the second and third landward vergent anticlines on the toe of the Cascadia accretionary complex off central Oregon (45 °N, 125° 30′W). In September 1993, we carried out a series of nine deep tow camera sled runs and nine ALVIN dives to examine the relationship between fluid venting, structure and canyon formation. We studied four canyons on the second and third landward vergent anticlines, as well as the apparently unfailed intercanyon regions along strike. All evidence of fluid expulsion is associated with the canyons; we found no evidence of fluid flow between canyons. Even though all fluid seeps are related to canyons, we did not find seeps in all canyons, and the location of the seeps within the canyons differed. On the landward facing limb of the second landward vergent anticline a robust cold seep community occurs at the canyon’s inflection point. This seep is characterized by chemosynthetic vent clams, tube worms and extensive authigenic carbonate. Fluids for this seep may utilize high-permeability flow paths either parallel to bedding within the second thrust ridge or along the underlying thrust fault before leaking into the overriding section. Two seaward facing canyons on the third anticlinal ridge have vent clam communities near the canyon mouths at approximately the intersection between the anticlinal ridge and the adjacent forearc basin. No seeps were found along strike at the intersection of the slope basin and anticlinal ridge. We infer that the lack of seepage along strike and the presence of seeps in canyons may be related to fluid flow below the forearc basin/slope unconformity (overpressured by the impinging thrust fault to the west?) directed toward canyons at the surface.     

悬移层风沙运动数值模拟

针对沙尘暴天气的风沙气固两相流,采用FLUENT软件,对悬移层的风沙运动进行了,2D数值模拟分析．比较了流体边界条件对流场的影响。风沙起动后,用紧贴地面的平面作为风沙起动床面的简化模拟面。本文提出一个新的沙粒起动体积浓度的表达式,并在计算中作为边界条件。在模拟中,避免了对床面复杂状况的直接描述。计算结果揭示了风沙流起动阶段沙尘的速度、体积浓度分布规律及其在边界条件影响下的变化规律。     

Simulating the 1999 Capbreton canyon turbidity current with a Cellular Automata model

A numerical model has been developed for the simulation of turbidity currents driven by nonuniform, non cohesive sediment and flowing over a complex three dimensional submarine topography. The model is based on an alternative approach known as Cellular Automata paradigm. The model is validated by comparing a simulation with a reported field-scale event. The chosen case is a turbidity current which occurred in Capbreton Canyon and was initiated by a storm in December 1999. Using data from recent oceanographic cruises, the deposit of the event has been precisely described, which constrain values of model parameters. The model simulates the 1999 turbidity current over the actual canyon topography and related turbidite using three different types of particle. The model successfully simulates areas of erosion and deposition in the canyon. It predicts the vertical and longitudinal grain size evolution, and shows that the fining-up sequence can be deposited by several phases of deposition and erosion related to the current energetic variation during its evolution. This result could explain the presence of intrabed contacts or the frequent lack of facies in Bouma sequences.     

湘粤赣“红三角”省际边界区旅游资源联动开发共生模式研究

在分析湘粤赣省际边界区“红三角”旅游资源联动开发共生条件的基础上,从开发空间结构、时间序列和参与主体三个维度探讨并构建了基于共生理论的“红三角”旅游资源联动开发的共生组织和共生行为模式,并通过构建共生模式5圈层结构图阐述了“红三角”旅游资源联动开发共生模式构成要素间的相互关系和相互作用。此圈层结构模式也能为省际边界区旅游资源联动开发提供借鉴。