重力资料精细处理及在珠江三角洲地震灾害研究中的应用   总被引：3，自引：0，他引：3  

乔计花  刘天佑  任镇寰 《地质灾害与环境保护》2003,14(4):77-80

对于珠江三角洲地区的断裂构造问题及其在地震灾害中的作用，随着该区经济的迅速发展，又重新引起人们的重视。本文利用小波变换和分形几何等新的数学方法对珠江三角洲地区的重力资料进行了精细处理．并获得了一些新的认识，认为北东东向断裂是该区的重要断裂，是珠江三角洲地区地震灾害产生的主要原因。  相似文献   

Theoretical regime equations for mobile gravel-bed rivers with stable banks   总被引：2，自引：1，他引：2  

Robert G. Millar   《Geomorphology》2005,64(3-4):207-220

A system of rational regime equations is developed for gravel-bed rivers with stable banks using the optimality theory (OT). The optimality theory is based on the premise that equilibrium river geometry is characterised by an optimum configuration, defined here as maximum sediment-transport efficiency. Theoretical dimensionless equations are derived for width, depth, slope, width/depth ratio, and meandering–braiding transition. Independent dimensionless variables comprise discharge, sediment concentration, and relative bank strength, μ′, which is defined as the ratio of the critical shear stresses for the bank and bed sediments. Discharge exponents and general form of the equations agree well with previously developed empirical relations. Relative bank strength, μ′, is used to parameterise the influence of riparian vegetation on bank strength and is evaluated by calibrating against observed width/depth ratio. Once calibrated, the hydraulic geometry of natural gravel rivers is well described by the theoretical equations, including discrimination between meandering and braiding channels. The results provide strong support for the assumption that equilibrium or regime river behavior is equivalent to an optimal state and underline the importance of bank strength and sediment load as controls on hydraulic geometry.  相似文献   

Controls on the geometry of tails around rigid circular inclusions: insights from analogue modelling in simple shear     

Santanu Bose  Fernando O. Marques   《Journal of Structural Geology》2004,26(12):2145-2156

We used analogue modelling to investigate the factors controlling tail geometry in porphyroclast systems. Results show that: (1) σ inclusions can develop in both slipping and non-slipping modes, but δ-inclusions only form in the latter. (2) σ inclusions develop when the mantle production rate is constant and the mantle is transected by the separatrix. δ inclusions form when the mantle is initially outside the separatrix and later comes inside this line. (3) In the slipping mode, the wedge-shaped tail of σ-inclusions always has a straight external surface parallel to the shear plane, whereas in the non-slipping mode the external surface is curved inwards (external embayments). (4) Together with earlier theoretical results, σ- and δ inclusions always show stair-stepping of tails when embedded in a viscous matrix under homogeneous simple shear deformation. (5) Maximum stair-stepping occurs in the slipping mode and is at least equal to the inclusion diameter. If our models bear significant similarity to nature, then (i) the straight or curved character of σ-inclusions could mean that they had, respectively, a slipping or non-slipping interface with the surrounding recrystallized matrix, and (ii) δ-inclusions may result from shear deformation under retrogressive metamorphic conditions in thrust systems.  相似文献   

Modelling Compositional Change: The Example of Chemical Weathering of Granitoid Rocks     

Hilmar von Eynatten  Carles Barceló-Vidal  Vera Pawlowsky-Glahn 《Mathematical Geology》2003,35(3):231-251

Perturbation on the simplex is an operation which can be used to numerically describe changes in the composition of, for example, soils, sediments, or rocks. The combination of perturbation and power transformation provides a strong tool for analyzing compositional linear processes in the simplex. When the process is constrained in the sense of a well-known starting (or final) composition, noncentred principal component analysis can be used to estimate the leading perturbation vector of the process. Applying these mathematical tools to chemical major element data from a weathering profile developed on granitoid rocks allows us to model the compositional changes associated with the process of chemical weathering. The comparison of these results with the compositional linear trend defined by erosional products of several of the world's major drainage systems yields close similarities. The latter observation allows for a mathematical formulation of a global mean weathering trend within the system Al₂O₃–CaO– Na₂O– K₂O. We further demonstrate the usefulness of the approach for validating processes behind individual trends and for combining the effects of different processes which modify the composition of soils, sediments, and rocks. Alternatives to the Chemical Index of Alteration (CIA) are discussed to obtain a translation-invariant scale for the process of chemical weathering.  相似文献   

Fault geometries from the space distribution of the 1990–1997 Sannio–Benevento earthquakes: inferences on the active deformation in Southern Apennines     

Giuseppe Vilardo  Rosa Nappi  Palma Petti  Guido Ventura 《Tectonophysics》2003,363(3-4):259-271

In this study, we analyze the recent (1990–1997) seismicity that affected the northern sector (Sannio–Benevento area) of the Southern Apennines chain. We applied the Best Estimate Method (BEM), which collapses hypocentral clouds, to the events of low energy (M_{d max}=4.1) seismic sequences in order to constrain the location and geometry of the seismogenetic structures. The results indicate that earthquakes aligned along three main structures: two sub-parallel structures striking NW–SE (1990–1992, Benevento sequence) and one structure striking NE–SW (1997, Sannio sequence). The southernmost NW–SE structure, which dips towards NE, overlies the fault that is likely to be responsible for a larger historical earthquake (I_{o max}=XI MCS, 1688 earthquake). The northernmost NW–SE striking structure dips towards SW. The NE–SW striking structure is sub-vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake. The spatio-temporal evolution of the 1990–1997 seismicity indicates a progressive migration from SE (Benevento) to NW (Sannio) associated to a deepening of hypocenters (i.e., from about 5 to 12 km). Hypocenters cluster at the interface between the major structural discontinuities (e.g., pre-existing thrust surfaces) or within higher rigidity layers (e.g., the Apulia carbonates). Available focal mechanisms from earthquakes occurred on the recognized NW–SE and NE–SW faults are consistent with dip-slip normal solutions. This evidences the occurrence of coexisting NW–SE and NE–SW extensions in Southern Apennines.  相似文献   

湘西喜眉山逆冲—推覆构造的特征与变形环境   总被引：1，自引：0，他引：1  

侯光久  索书田  魏启荣  郑贵洲 《地质通报》1998,(1)

论述了雪峰山西北部喜眉山逆冲—推覆构造的几何学、运动学特征,并用方解石ｅ双晶求得逆冲—推覆构造断层岩形成时的差异应力为１００～１２５ＭＰａ,变形温度为１５０～２００℃,逆冲作用主要发生于燕山运动时期。  相似文献   

Reach‐scale channel geometry of a mountain river     

Ellen Wohl  Jessica N. Kuzma  Nancy E. Brown 《地球表面变化过程与地形》2004,29(8):969-981

Mountain rivers can be subject to strong constraints imposed by changes in gradient and grain size supplied by processes such as glaciation and rockfall. Nonetheless, adjustments in the channel geometry and hydraulics of mountain rivers at the reach scale can produce discernible patterns analogous to those in fully alluvial rivers. Mountain rivers can differ in that imposed reach‐scale gradient is an especially important control on reach‐scale channel characteristics, as indicated by examination of North St Vrain Creek in Colorado. North St Vrain Creek drains 250 km² of the Rocky Mountains. We used 25 study reaches within the basin to examine controls on reach‐scale channel geometry. Variables measured included channel geometry, large woody debris, grain size, and mean velocity. Drainage area at the study reaches ranged from 2·2 to 245 km², and gradient from 0·013 to 0·147 m m^?1. We examined correlations among (1) potential reach‐scale response variables describing channel bankfull dimension and shape, hydraulics, bedform wavelength and amplitude, grain size, ?ow resistance, standard deviation of hydraulic radius, and volume of large woody debris, and (2) potential control variables that change progressively downstream (drainage area, discharge) or that are likely to re?ect a reach‐speci?c control (bed gradient). We tested the hypothesis that response variables correlate most strongly with local bed gradient because of the segmented nature of mountain channels. Results from simple linear regression analyses indicate that most response variables correlate best with gradient, although channel width and width/depth ratio correlate best with discharge. Multiple regression analyses using Mallow's C_p selection criterion and log‐transformation of all variables produced similar results in that most response variables correlate strongly with gradient. These results suggest that the hypothesis is partially supported: channel bed gradient is likely to be a good predictor for many reach‐scale response variables along mountain rivers, but discharge is also an important predictor for some response variables. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Medical imaging challenges photogrammetry     

Petros Patias   《ISPRS Journal of Photogrammetry and Remote Sensing》2002,56(5-6)

In its current status, medical imaging involves a wide range of imaging modalities and is faced with a range of interesting research questions, while trying to automatically convert the huge floods of image data to useful information. The major characteristic of the developed techniques is the exploitation of visual similarities or differences; that is basically qualitative treatment of the information inherent in the images. This proves to be a major shortcoming, leading to erroneous or unreliable results in many cases. To this end, technology transfer from the part of photogrammetry can be proven very beneficial. Such a contribution can be geared by the fact that photogrammetry has developed efficient tools for accounting for imaging formation geometry. These tools, appropriately tuned for medical applications, can accelerate the technology transfer across the involved disciplines. Understanding the possible photogrammetric contributions by the medical imaging experts, and realizing the medical problems in photogrammetric terms by the photogrammetrists, remains a major barrier to this transfer. The intended scope of this paper is to provide a foundation for exchange of ideas and provoke photogrammetric research interest in these issues.  相似文献   

基于分形理论的水系要素制图综合研究   总被引：9，自引：1，他引：9  

何宗宜  阮依香  尹为利  陈涛 《武汉大学学报(信息科学版)》2002,27(4):427-431

在研究水系要素具有分形现象的基础上，提出了水系要素的分维数的确定方法，并利用水系的分数维规律进行地图制图综合，取到了较好的结果。  相似文献   

云南漾弓江流域城乡聚落形态信息提取与分形分析   总被引：7，自引：0，他引：7  

蒋雪中  杨山  沈婕  赵锐 《遥感学报》2002,6(4):294-298

利用 1996年 2月和 1999年 11月的TM影像 ,通过对漾弓江流域的遥感影像的光谱特征分析 ,建立地物光谱模型 ,提取区域城乡聚落的时空分布信息。在此基础上 ,根据分形几何理论计算漾弓江流域城乡聚落不同时段空间形态的分形维数 ,从其变化分析流域内聚落空间形态的特征。结果表明 ,欠发达地区城乡聚落空间形态具有分形现象 ,并且城市与农村集镇的分形维数变化不一致 ,1996年丽江地震和 1998年大丽线的开通加速了丽江城和鹤庆城的发展 ,使其形态趋于复杂、不稳定性增大。  相似文献