Drainage basin sensitivity to tectonic and climatic forcing: implications of a stochastic model for the role of entrainment and erosion thresholds

Long‐term average rates of channel erosion and sediment transport depend on the frequency–magnitude characteristics of ?ood ?ows that exceed an erosion threshold. Using a Poisson model for rainfall and runoff, analytical solutions are developed for average rates of stream incision and sediment transport in the presence of such a threshold. Solutions are derived and numerically tested for three erosion/transport formulas: the Howard–Kerby shear‐stress incision model, the Bridge–Dominic sediment transport model, and a generic shear‐stress sediment transport model. Results imply that non‐linearity resulting from threshold effects can have a ?rst‐order impact on topography and patterns of dynamic response to tectonic and climate forcing. This non‐linearity becomes signi?cant when fewer than about half of ?ood events are capable of detaching rock or sediment. Predicted morphology and uplift‐gradient scaling is more closely consistent with observations and laboratory experiments than conventional slope‐linear or shear‐linear erosion laws. These results imply that particle detachment thresholds are not details that can be conveniently ignored in long‐term landscape evolution models. Copyright © 2004 John Wiley & Sons, Ltd.     

关于网外地震的定位问题--利用福建区域数字地震台网资料测定台湾地震震源位置

针对地壳内部的网外地震震源的定位问题，由震相组合成不同的方程组，利用均值寻查定位法迭代求解。在选取地球物理参数模型时，考虑了台湾地震部门定位时所用的模型和华南地区地震走时表等。利用福建数字地震台网记录到的绕射波Pn、Sn的到时资料，通过定位程序测定了134个位于台湾区域的壳内地震的震源位置。测定结果与台湾地震部门在其网址上公布的结果进行比对．平均震中位詈相差9km．震源深度相差8km．     

渭河断陷盆地及邻近地区的Q值速度场分布特征与地震活动性

利用西安数字遥测地震台网记录的数字地震资料．采用P↑-波初动半周期方法．得到了渭河断陷盆地及邻近地区的Q值分布。结果表明，Q值分布与20km深度P↑-波速度分布有较好的一致性．并与该区域的地震活动性密切相关。     

无需初值的RPC模型参数求解算法研究

针对国内外研究者求解RPC(Rational Polynom ial Cam era)模型参数的算法需要初值及迭代处理,且求解过程相当复杂的缺憾,提出基于全球DEM无需初值的RPC模型参数求解算法。利用SPOT-5卫星影像进行试验,获得该算法对线阵推扫式卫星遥感影像有意义的结论。对SPOT-5卫星影像在利用严格成像模型求解RPC模型参数时,进行了控制点格网大小及高程分层数对求解精度的影响试验,得出:对SPOT-5卫星影像,采用控制点的格网大小为20像素×20像素、高程分层数为3时,可以达到精度和效率的平衡。     

The compatibility conditions in altimetry–gravimetry boundary value problems

The role of compatibility conditions for altimetry–gravimetry boundary value problems (AGBVPs) is quite complicated by way of: guaranteeing the existence of the solution; smoothing the data (boundary conditions) at the boundary; and providing a higher level of regularization and smoothness to the solution. Pseudo-differential operators (PDOs) can be applied not only for the reformulation of AGBVPs in a simple way, but also for imposing compatibility conditions at the coastline. It is shown here that spherical PDOs can be combined with the theory of spherical harmonics and spherical wavelets to obtain a numerical solution for AGBVPs with compatibility conditions along the coastline. The role of compatibility conditions, is summarized and emphasized and compatibility conditions are given in an explicit form based on the combined representation of functionals of the disturbing potential in terms of spherical harmonics, spherical PDOs and wavelets. Numerical aspects of the application of the compatibility conditions to a case-study area in Canada are discussed.     

云南地震数字遥测台网子台地动噪声分析

介绍了云南数字遥测台网的基本情况，阐述了地动噪声有效值和功率谱的计算方法。对选取的资料进行预处理后，计算分析了云南数字遥测台网全部子台的地动噪声水平，按地动噪声水平对子台进行了分类。指出了地动噪声分析对台网建设的作用。     

Active sensing using impedance‐based ARX models and extreme value statistics for damage detection

In this paper, the applicability of an auto‐regressive model with exogenous inputs (ARX) in the frequency domain to structural health monitoring (SHM) is established. Damage sensitive features that explicitly consider non‐linear system input/output relationships are extracted from the ARX model. Furthermore, because of the non‐Gaussian nature of the extracted features, Extreme Value Statistics (EVS) is employed to develop a robust damage classifier. EVS provides superior performance to standard statistical methods because the data of interest are in the tails (extremes) of the damage sensitive feature distribution. The suitability of the ARX model, combined with EVS, to non‐linear damage detection is demonstrated using vibration data obtained from a laboratory experiment of a three‐story building model. It is found that the vibration‐based method, while able to discern when damage is present in the structure, is unable to localize the damage to a particular joint. An impedance‐based active sensing method using piezoelectric (PZT) material as both an actuator and a sensor is then investigated as an alternative solution to the problem of damage localization. Copyright © 2005 John Wiley & Sons, Ltd.     

崇明地震台FGE磁通门磁力仪D分量基线值的确定

基线值是考察记录仪运行是否稳定可靠的一个重要指标。本文以记录仪的D分量为例,通过认真仔细地分析与探索,使用数据处理的方法,解决了崇明台FGE磁通门磁力仪基线值不稳定的问题。这对基线值的确定和日常的数据处理都具有一定的指导意义。     

山东黄河流域下游土壤粒度和深度试验成果

以黄河流域下游野外获得的土壤粒度和深度纵剖面试验资料为基础，分析了黄河流域下游不同土壤类型区、不同地貌单元的土壤粒级组成、元素在各粒级组中的分配特征和元素在土壤纵剖面中的含量、纵向变化规律，探讨了其在生态地球化学调查中的意义。确定了能代表区域内土壤主要物质组成的粒级范围，提出了本区生态地球化学调查的最佳样品筛分加工方案和表层、深层土壤样品采集的有效深度和层位。     

喀斯特石漠化景观及其土地的生态效应——以贞丰县为例

利用喀斯特石漠化生态脆弱区贵州贞丰县2004年的ASTER遥感影像,解译了全县的喀斯特石漠化现状,并从景观生态学的角度指出轻、中、强、极度石漠化存在不同的空间分布格局.与此同时,作者还把石漠化的景观格局和其土地生态价值的分布频率结合起来,并从生态系统服务功能的角度定量计算了相应喀斯特石漠化土地的相对生态价值,评价了研究区石漠化土地的生态效应.结果表明,贞丰县270个村的生态价值整体偏低,全县极大值为1.016,极小值为0.286;不同区域之间的总体生态价值差异较大,生态价值相对较好的地区主要集中在非喀斯特地带,而在中度、强度、极强度石漠化地区生态价值很低.