Deep structure of the Amur lithospheric Plate border zone

Based on the study of the deep Amur Plate border structure, seismogravimetric (density) and geoelectric sections of the plate lithosphere crossing geologically and seismically defined plate boundaries are compiled to construct a three-dimensional model of its lithosphere. The model demonstrates the almost ring structure of the plate with its inner part dipping for 50 km and uplifted fringing. The plate boundary zone consists of orogenic belts (Mongol-Okhotsk, Selenga-Stanovoi, Transbaikal, and Sikhote-Alin) and margins of the Siberian and North China platforms. The plate boundaries are described by mantle diapirism models with a largely bilateral inclined dip of its bordering belts.     

Direct finite element method for nonlinear earthquake analysis of concrete dams: Simplification,modeling, and practical application

A direct finite element (FE) method for nonlinear response history analysis of semi-unbounded dam-water-foundation systems has recently been presented. The analysis procedure employs standard viscous-damper absorbing boundaries to model the semi-unbounded foundation and fluid domains and specifies the seismic input as effective earthquake forces—determined from a control motion defined at the foundation surface—at these boundaries. Presented in this paper are several simplifications to this direct FE method that greatly facilitates its implementation in commercial FE software. Also addressed is the modeling of the principal nonlinear mechanisms for concrete dams, calibration of damping in the numerical model to ensure consistency with values measured at actual dams, and practical procedures for implementation of the direct FE method with a commercial FE program.     

颗粒离散单元法动力人工边界设置方法

采用颗粒离散单元法进行动力计算时,人工截断边界上需设置吸收边界条件,以防止波的反射。鉴于颗粒离散单元数值计算模型的人工边界上颗粒单元半径大小不一、边界面凸凹不平,在连续介质的黏性、黏弹性、自由场边界条件方程基础之上,推导出适用于离散介质的等效方程。在离散介质的黏性边界条件等效方程中引入微调系数,提出比值迭代法以快速确定其最优值,以实现对波的最佳吸收。采用二维颗粒离散单元计算软件PFC2D,分别建立黏性、黏弹性、自由场边界条件相关数值分析模型,探讨颗粒分布模式对黏性边界上颗粒单元半径、速度分布及比值迭代过程的影响;采用外源波动算例及经典Lamb问题算例验证黏弹性边界设置方法的正确性;通过隧洞算例检验提出的自由场边界条件设置方法的正确性。     

基于Monte Carlo模拟的三维剖面地质界线不确定性分析

三维剖面地质界线是构建三维地质结构模型的重要基础数据,其不确定性会影响三维模型的几何形态和属性分布。以单一分布为假设前提的统计学不确定性分析方法掩盖了其他概率分布特征对模型的影响。突破单一误差分布条件的假设前提,本文使用Monte Carlo方法模拟了不同概率分布情况下地质剖面数据中地质界线的抽样采集,以及地质界线空间分布的不确定性;依托地质界线空间位置与地质属性的耦合关系,提出了用地质属性概率分布实现地质界线空间不确定性的定量可视化,并结合实际地质剖面探讨了多种概率分布条件下地质界线的空间不确定性。实例研究表明,基于Monte Carlo模拟的不确定性分析方法可以突破单一误差分布假设条件,结合地质属性概率可充分揭示出建模数据的内在不确定性与模型外在要素形态之间的耦合关系。     

Sharp spatially constrained inversion with applications to transient electromagnetic data

Time‐domain electromagnetic data are conveniently inverted by using smoothly varying 1D models with fixed vertical discretization. The vertical smoothness of the obtained models stems from the application of Occam‐type regularization constraints, which are meant to address the ill‐posedness of the problem. An important side effect of such regularization, however, is that horizontal layer boundaries can no longer be accurately reproduced as the model is required to be smooth. This issue can be overcome by inverting for fewer layers with variable thicknesses; nevertheless, to decide on a particular and constant number of layers for the parameterization of a large survey inversion can be equally problematic. Here, we present a focusing regularization technique to obtain the best of both methodologies. The new focusing approach allows for accurate reconstruction of resistivity distributions using a fixed vertical discretization while preserving the capability to reproduce horizontal boundaries. The formulation is flexible and can be coupled with traditional lateral/spatial smoothness constraints in order to resolve interfaces in stratified soils with no additional hypothesis about the number of layers. The method relies on minimizing the number of layers of non‐vanishing resistivity gradient, instead of minimizing the norm of the model variation itself. This approach ensures that the results are consistent with the measured data while favouring, at the same time, the retrieval of horizontal abrupt changes. In addition, the focusing regularization can also be applied in the horizontal direction in order to promote the reconstruction of lateral boundaries such as faults. We present the theoretical framework of our regularization methodology and illustrate its capabilities by means of both synthetic and field data sets. We further demonstrate how the concept has been integrated in our existing spatially constrained inversion formalism and show its application to large‐scale time‐domain electromagnetic data inversions.     

基于钻孔数据任意边域地层分界面B-Rep建模研究

对相邻钻孔数据的类型进行了分析,对不同连续性和规则性的地层分界面进行了建模.考虑地层分界面的光滑性和整体控制性,运用边界表示法(B-Rep)和B样条曲面重构地层分界面,为地层建模提供了一种新的方法.建模研究表明:在钻孔数据前处理算法的基础上,B-Rep能够建立连续型、非连续型、空洞型等任意边域的地层分界面.     

Representing geographical objects with scale‐induced indeterminate boundaries: A neural network‐based data model

The degree of uncertainty of many geographical objects has long been known to be in intimate relation with the scale of its observation and representation. Yet, the explicit consideration of scaling operations when modeling uncertainty is rarely found. In this study, a neural network‐based data model was investigated for representing geographical objects with scale‐induced indeterminate boundaries. Two types of neural units, combined with two types of activation function, comprise the processing core of the model, where the activation function can model either hard or soft transition zones. The construction of complex fuzzy regions, as well as lines and points, is discussed and illustrated with examples. It is shown how the level of detail that is apparent in the boundary at a given scale can be controlled through the degree of smoothness of each activation function. Several issues about the practical implementation of the model are discussed and indications on how to perform complex overlay operations of fuzzy maps provided. The model was illustrated through an example of representing multi‐resolution, sub‐pixel maps that are typically derived from remote sensing techniques.     

Instability of flows near the onset of convection in a rotating layer with stress-free horizontal boundaries

We investigate instability of convective flows of simple structure (rolls, standing and travelling waves) in a rotating layer with stress-free horizontal boundaries near the onset of convection. We show that the flows are always unstable to perturbations, which are linear combinations of large-scale modes and short-scale modes, whose wave numbers are close to those of the perturbed flows. Depending on asymptotic relations of small parameters α (the difference between the wave number of perturbed flows and the critical wave number for the onset of convection) and ε (ε² being the overcriticality and the perturbed flow amplitude being O(ε)), either small-angle or Eckhaus instability is prevailing. In the case of small-angle instability for rolls the largest growth rate scales as ε^8/5, in agreement with results of Cox and Matthews (Cox, S.M. and Matthews, P.C., Instability of rotating convection. J. Fluid. Mech., 2000, 403, 153–172) obtained for rolls with k = k _c . For waves, the largest growth rate is of the order ε^4/3. In the case of Eckhaus instability the growth rate is of the order of α².     

Institutionalization of Racial Inequality in Local Political Geographies

Municipalities create a local political geography that can institutionalize subordinate positions for minority groups. Most importantly, local governments determine which areas are incorporated into a municipality through annexation and which are excluded. Through these powers, local governments can diminish or deny minority political standing in local affairs, limit access to public services, and reduce the value of minority property. The boundaries are a component of racial residential segregation. Racially disparate application of local governments' power to shape local political geography creates barriers to equality that are difficult to discern on the ground, but which can be made visible by the mapping of spatial data. This study presents four cases where governmental decisions concerning a municipal boundary have institutionalized racial inequality, which is documented with maps created from public GIS data and other public records (e.g., City Council meeting minutes) as well as legal documents. This pattern of systematic exclusion of minority neighborhoods is receiving attention in the legal community, but studies in the social sciences have been limited.