The spatial variation of earthquake ground motion and effects of local site conditions
地震 高中英语阅读理解
地震高中英语阅读理解Earthquakes: Unraveling the Mysteries of the Earth's Dynamic ForcesEarthquakes, the sudden and often violent shaking of the Earth's surface, have captivated the human imagination for centuries. These powerful natural phenomena have the ability to reshape the landscape, topple structures, and claim countless lives, leaving an indelible mark on the collective consciousness of humanity. As we delve into the intricate workings of earthquakes, we uncover a complex tapestry of scientific understanding that not only illuminates the forces that shape our planet but also highlights the ongoing efforts to mitigate the devastating impact of these events.At the heart of earthquake science lies the theory of plate tectonics, which revolutionized our understanding of the Earth's dynamic interior. This theory posits that the Earth's surface is composed of a series of massive plates, constantly in motion, driven by the convection of the planet's molten interior. The boundaries between these plates are the primary loci of seismic activity, as the relentless forces of compression, tension, and shear create immense stresses that are ultimately released in the form of earthquakes.When tectonic plates collide, one plate is typically forced beneath the other, a process known as subduction. This subduction zone is a hotbed of seismic activity, as the descending plate generates intense friction and pressure, triggering a series of earthquakes. The Pacific Ring of Fire, a region encircling the Pacific Ocean, is a prime example of this, with a high concentration of active volcanoes and frequent earthquake occurrences.Earthquakes, however, are not limited to plate boundaries; they can also occur within the interior of tectonic plates, often along pre-existing fault lines. These intraplate earthquakes can be equally devastating, as evidenced by the 2011 Tohoku earthquake in Japan, which triggered a devastating tsunami and caused widespread destruction.The magnitude of an earthquake, a measure of the energy released during the event, is a crucial factor in determining its potential for destruction. The Richter scale, developed in the 1930s by American seismologist Charles Richter, provides a logarithmic scale for measuring earthquake magnitude, with each unit increase representing a tenfold increase in the amount of energy released. The most powerful earthquakes, often referred to as "megaquakes," can reach magnitudes exceeding 9.0 on the Richter scale, releasing staggering amounts of energy and causing catastrophic damage.While the raw power of earthquakes is awe-inspiring, the true tragedy lies in the human cost of these events. Densely populated urban centers, often built atop vulnerable geological structures, bear the brunt of the destruction, with buildings collapsing, infrastructure crumbling, and lives lost. The 2010 Haiti earthquake, for instance, claimed over 300,000 lives and left countless more injured or displaced, highlighting the devastating impact of these natural disasters on vulnerable communities.In the face of such immense challenges, the scientific community has dedicated itself to understanding the complex mechanisms that drive earthquakes, with the ultimate goal of improving our ability to predict and mitigate their consequences. Advancements in seismic monitoring technology, the development of early warning systems, and the implementation of stringent building codes have all played a crucial role in reducing the loss of life and property during earthquakes.Yet, the unpredictable nature of these events remains a formidable challenge. Earthquake prediction, long the Holy Grail of seismology, has proven to be an elusive goal, as the complex interplay of factors that trigger seismic events continues to defy our best efforts at forecasting. Nonetheless, scientists remain undaunted, leveraging the power of data analysis, computational modeling, and interdisciplinary collaboration to unravel the mysteries of the Earth'sdynamic forces.Beyond the scientific realm, the impact of earthquakes has also shaped the cultural and societal landscape of affected regions. The resilience and adaptability of communities in the face of such adversity have inspired awe and admiration, as people come together to rebuild and recover in the aftermath of these events. The lessons learned from past earthquakes have informed urban planning, emergency response protocols, and disaster management strategies, ensuring that we are better prepared to face the challenges that lie ahead.As we continue to grapple with the realities of a changing climate and the increasing frequency and intensity of natural disasters, the study of earthquakes assumes an even greater importance. By understanding the complex interplay of tectonic forces, we can develop more effective strategies for mitigating the impact of these events, protecting vulnerable populations, and ensuring the long-term resilience of our communities.In the end, the story of earthquakes is one of both humility and resilience. It reminds us of the raw power of nature and the fragility of our human constructs, but it also inspires us to push the boundaries of scientific understanding, to innovate, and to work together in the face of adversity. As we continue to unravel themysteries of the Earth's dynamic forces, we are reminded of our place in the grand tapestry of our planet, and the vital importance of our collective efforts to safeguard our future.。
国际物理林匹克竞赛试题Theoretical_Exam_Solution_2_English
Solution- Theoretical Question 2A Piezoelectric Crystal Resonator under an Alternating Voltage Part A(a) Refer to Figure A1. The left face of the rod moves a distance v ∆t while thepressure wave travels a distance u ∆t with ρ/Y u =. The strain at the left face isuv t u t v S -=-==∆∆∆(A1a)*1 From Hooke’s law, the pressure at the left face is uv uv Y YS p ρ==-= (A1b)*(b) The velocity v is related to the displacement ξ as in a simple harmonic motion (or a uniform circular motion, as shown in Figure A2) of angular frequency ku =ω. Therefore, if )(sin ),(0t u x k t x -=ξξ, then)(cos ),(0t u x k ku t x v --=ξ. (A2)*The strain and pressure are related to velocity as in Problem (a). Hence,)(cos /),(),(0t u x k k u t x v t x S -=-=ξ (A3)*)(cos ),()(cos ),(),(002t u x k kY t x YS t u x k u k t x uv t x p --=-=--==ξξρρ (A4)*-------------------------------------------------------------------------------------------------)(cos ),(0t u x k ku t t x v --==ξ∆ξ∆, )(cos ),(0t u x k k x t x S -==ξ∆ξ∆, )(cos ),(0t u x k kY xY t x p --=-=ξ∆ξ∆. -------------------------------------------------------------------------1 An equations marked with an asterisk contains answer to the problem.t=0∆t/2 Figure A1 ∆t Figure A2Part B(c) Since the angular frequency ω and speed of propagation u are given, the wavelength is given by λ = 2π / k with k = ω / u . The spatial variation of the displacement ξ is therefore described by)2(cos )2(sin )(21b x k B b x k B x g -+-= (B1) Since the centers of the electrodes are assumed to be stationary, g (b /2) = 0. This leads to B 2 = 0. Given that the maximum of g (x ) is 1, we have A = ±1 and)2(sin )(b x u x g -±=ω (B2)* Thus, the displacement ist b x u t x ωωξξcos )2(sin 2),(0-±= (B3) (d) Since the pressure p (or stress T ) must vanish at the end faces of the quartz slab (i.e., x = 0 and x = b ), the answer to this problem can be obtained, by analogy, from the resonant frequencies of sound waves in an open pipe of length b . However, given that the centers of the electrodes are stationary, all evenharmonics of the fundamental tone must be excluded because they have antinodes, rather than nodes, of displacement at the bisection plane of the slab.Since the fundamental tone has a wavelength λ = 2b , the fundamentalfrequency is given by )2/(1b u f =. The speed of propagation u is given by33101045.51065.21087.7⨯=⨯⨯==ρYu m/s (B4) and, given that b =1.00⨯10-2 m, the two lowest standing wave frequencies are)kHz (27321==b u f , )kHz (81823313===bu f f (B5)* -------------------------------------------------------------------------------------------------[Alternative solution to Problems (c) and (d)]: A longitudinal standing wave in the quartz slab has a displacement node at x = b/2. It may be regarded as consisting of two waves traveling in opposite directions. Thus, its displacement and velocity must have the following form)]2(sin )2([sin cos )2(sin 2),(ut b x k ut b x k t b x k t x m m +-+--=-=ξωξξ (B6) t b x k ut b x k ut b x k ku t x v m m ωωξξsin )2(sin 2)]2(cos )2([cos ),(--=+-----= (B7) where ω = k u and the first and second factors in the square brackets represent waves traveling along the +x and –x directions, respectively. Note that Eq. (B6) is identical to Eq. (B3) if we set ξm = ±ξ0.For a wave traveling along the –x direction, the velocity v must be replaced by –v in Eqs. (A1a) and (A1b) so that we haveuv S -= and uv p ρ= (waves traveling along +x ) (B8) uv S = and uv p ρ-= (waves traveling along –x ) (B9) As in Problem (b), the strain and pressure are therefore given byt b x k k ut b x k ut b x k k t x S m m ωξξcos )2(cos 2)]2(cos )2(cos [),(-=+------= (B10) t b x k u ut b x k ut b x k u t x p m m ωωξρωξρcos )2(cos 2)]2(cos )2([cos ),(--=+-+---= (B11) Note that v , S , and p may also be obtained by differentiating ξ as in Problem (b).The stress T or pressure p must be zero at both ends (x = 0 and x = b ) of the slab at all times because they are free. From Eq. (B11), this is possible only if 0)2/cos(=kb or,5,3,1,2====n n b ff b u kb πλπω (B12) In terms of wavelength λ, Eq. (B12) may be written as,5,3,1,2==n nb λ. (B13) The frequency is given by,5,3,1,22====n Y b n b nu u f ρλ. (B14) This is identical with the results given in Eqs. (B4) and (B5).--------------------------------------------------------------------------------------------------- (e) From Eqs. (5a) and (5b) in the Question, the piezoelectric effect leads to the equations)(E d S Y T p -= (B15)E d Y S Yd T pT p )1(2εεσ-+= (B16)Because x = b /2 must be a node of displacement for any longitudinal standingwave in the slab, the displacement ξ and strain S must have the form given in Eqs. (B6) and (B10), i.e., with ku =ω,)cos()2(sin ),(φωξξ+-=t b x k t x m (B17) )cos()2(cos ),(φωξ+-=t b x k k t x S m (B18) where a phase constant φ is now included in the time-dependent factors.By assumption, the electric field E between the electrodes is uniform anddepends only on time:ht V h t V t x E m ωcos )(),(==. (B19) Substituting Eqs. (B18) and (B19) into Eq. (B15), we have]cos )cos()2(cos [t V hd t b x k k Y T m p m ωφωξ-+-= (B20) The stress T must be zero at both ends (x = 0 and x = b ) of the slab at all times because they are free. This is possible only if φ = 0 andhV d kb k m p m =2cos ξ (B21) Since φ = 0, Eqs. (B16), (B18), and (B19) imply that the surface charge density must have the same dependence on time t and may be expressed ast x t x ωσσcos )(),(= (B22)with the dependence on x given byh V d Y b x k kb d Y hV d Y b x k k Yd x m T p T p mT p T m p )]1()2(cos 2cos [)1()2(cos )(222εεεεξσ-+-=-+-= (B23)* (f) At time t , the total surface charge Q (t ) on the lower electrode is obtained by integrating ),(t x σin Eq. (B22) over the surface of the electrode. The result is)]1()2tan 2([)]1()2tan 2()[()]1()2(cos 2cos [)(1),()(1)()(2202202200ααεεεεεσσ-+=-+=-+-===⎰⎰⎰kb kb C d Y kb kb d Y h bw dx d Y b x k kb d Y h w dx w x V wdx t x t V t V t Q Tp T p T b T p T p b m b (B24) where h bw C T ε=0, 322221082.906.427.110)25.2(--⨯=⨯⨯==T p d Y εα (B25)* (The constant α is called the electromechanical coupling coefficient .) Note : The result C 0 = εT bw /h can readily be seen by considering the static limit k = 0 of Eq. (5) in the Question. Since x x ≈tan when x << 1, we have02200)]1([)(/)(lim C C t V t Q k =-+≈→αα (B26)Evidently, the constant C 0 is the capacitance of the parallel-plate capacitor formed by the electrodes (of area bw ) with the quartz slab (of thickness h and permittivityεT) serving as the dielectric medium. It is therefore given by εT bw/h.(B47)*。
汶川Ms8.0地震前区域性地电阻率异常初步研究
汶川Ms8.0地震前区域性地电阻率异常初步研究朱涛【期刊名称】《地震学报》【年(卷),期】2013(35)1【摘要】对汶川Ms8.0地震震中周围17个台站的地电阻率观测资料进行了处理.以2007年的地电阻率观测数据为背景值,计算出每一个台站NS和EW两个测向2008年的地电阻率月均值相对变化的绝对值,然后选择较大的值作为当月的相对变化值.最终获得了汶川地震前5个月的地电阻率异常变化图像.结果表明,随着发震时间的临近,地电阻率异常分布的范围逐渐缩小,并最终集中分布在汶川地震震中附近；在临近发震时间(2008年3,4月),地电阻率异常分布的长轴方向与汶川M8.0地震的破裂方向、龙门山断裂带走向或地震烈度分布的长轴方向几乎垂直,而与其震源机制解的主压应力轴方向基本一致.%Geo-resistivity data recorded at 17 stations around the epicenter of the Wenchuan MS8. 0 earthquake were processed. Taken the geo-resistivity data in 2007 as background values,the absolute values of relative variations of monthly average value in NS and EW directions in 2008 were calculated, and then the larger one was chosen as the relative variation of each month. At last the variation images of geo-resistivity anomaly for the 5 months before the Wenchuan earthquake were obtaind. The results show that, as the occurrence time of the earthquake drew near, the spatial variation of geo-resistivity anomaly shrinked gradually and finally concentrated in the area near the epicenter. In the period just before the earthquake (March and April, 2008), themajor axis of geo resistivity anomaly was almost perpendicular to the rupture direction of the Wenchuan MS8. 0 earthquake and the strike of Longmenshan fault or the major axis of the distribution of seismic intensity, but nearly parallel to the principal compressive stress axis from focal mechanism solution.【总页数】8页(P18-25)【作者】朱涛【作者单位】中国北京 100081 中国地震局地球物理研究所(地震观测与地球物理成像重点实验室)【正文语种】中文【中图分类】P319【相关文献】1.2008年汶川Ms8.0地震前定点形变高频异常特征的研究 [J], 武善艺;刘琦;龚丽文;张治广2.2018年汶川Ms8.0地震前成都台NE向地电阻率趋势异常的数值模拟 [J], 钱家栋;张学民;王亚璐;李雪浩3.汶川Ms8.0地震前成都台NE测线地电阻率异常的进一步研究 [J], 钱家栋;马钦忠;李劭秾4.汶川Ms8.0级和芦山Ms7.0级地震与通渭地电阻率异常关系研究 [J], 陈彦平;王燕;洪旭瑜;张磊;漆银录;张世明5.基于断层虚位错模式讨论2008年汶川Ms8.0地震前视电阻率变化 [J], 解滔;于晨;王亚丽;李美;卢军因版权原因，仅展示原文概要，查看原文内容请购买。
气藏工程翻译版课件Chapter3 Gas Volumes and Material-Balance Calculations
气体体积和物质平衡计算
3.1 Introduction
3.2 Volumetric Methods体积的方法
• Volumetric dry-gas reservoirs • 体积干气气藏 • Dry-gas reservoirs with water influx干水驱气藏 • Volumetric wet-gas and gas-condensate reservoirs • 体积湿天然气和凝析气藏
Determination of z-factor for wet gas and condensate gas:
ppc75.6813.10h3.6h2 psia Tpc16.9234.95h74.0h2 °
R
Gas specific gravity at reservoir conditions
h 1 1 .7y 6 H 2 S 1 7 1 .y 5 H 2 S 1 y y C N 2 2 9 O 0 y .C 9 6 2 O 6 y y H N 2 2 O 7 0 .6 22 y H 2 O 20
3.3 Material-Balance Method物质平衡法
Material balance equation:
(1).structural and stratigraphic cross-sectional maps
构造和地层剖面图
(2).subsurface contour maps 地下等高线图 (3).subsurface isopachous maps 底层等原因
3.2 Volumetric Method
基于协同克里格插值和地理加权回归模型的土壤属性空间预测比较
基于协同克里格插值和地理加权回归模型的土壤属性空间预测比较一、本文概述Overview of this article本文旨在比较协同克里格插值（Co-Kriging）和地理加权回归模型（Geographically Weighted Regression，GWR）在土壤属性空间预测中的应用效果。
土壤属性空间预测是农业、环境科学和地球科学等领域的重要研究内容，对于土地资源管理、生态环境保护以及农业可持续发展具有重要意义。
协同克里格插值和地理加权回归模型是两种常用的空间预测方法，它们各自具有独特的优点和适用范围。
This article aims to compare the application effects of Co Kriging interpolation and Geographically Weighted Regression (GWR) models in soil attribute spatial prediction. Soil attribute spatial prediction is an important research content in fields such as agriculture, environmental science, and earth science, which is of great significance for land resource management, ecological environment protection, and sustainable development of agriculture. Collaborative Kriginginterpolation and geographically weighted regression models are two commonly used spatial prediction methods, each with unique advantages and applicability.协同克里格插值是一种基于空间统计学的插值方法，它利用多个相关变量的空间分布信息，通过计算权重系数来预测未知点的属性值。
空间结构多维地震响应改进组合准则
第 39 卷第 5 期2023 年10 月结构工程师Structural Engineers Vol. 39 ， No. 5Oct. 2023空间结构多维地震响应改进组合准则曲扬1，*唐潮1陈刚1程建军1罗永峰2（1.中建八局第三建设有限公司，南京 210046； 2.同济大学土木工程学院，上海 200092）摘要现有以主轴模型为理论基础的多维地震响应组合准则由于忽略了多维相关性，通常低估空间结构实际的多维地震响应量。
针对此问题，首先指出了经典反应谱CQC准则和SRSS准则在多维地震情形下的不足，在此基础上，提出并定义多维分量相关系数，据此量化多维地震动分量之间的相关程度，采用并行计算技术，进行大量多维地震动分量的相关性分析，验证其合理性。
将多维分量相关系数引入SRSS准则，提出能够考虑多维地震响应相关性的改进组合准则。
将该准则运用于球面网壳和鞍型网壳算例的时程分析和推覆分析响应组合中，并与SRSS准则进行对比分析，计算结果表明：改进组合准则的计算精度较高，最大位移的计算误差控制在15%以内，能够合理预测空间结构多维位移响应的分布规律和变化趋势，显著改善了SRSS准则低估多维响应的缺点，同时保留了较高的分析效率，便于应用。
关键词空间结构，多维地震，组合准则，相关性分析Multicomponent Correlated Combination Rule for MultidimensionalSeismic Response of Spatial StructuresQU Yang1，*TANG Chao1CHEN Gang1CHENG Jianjun1LUO Yongfeng2（1.The Third Construction Co. Ltd. of China Construction Eighth Engineering Division， Nanjing 210046， China；2.College of Civil Engineering，Tongji University， Shanghai 200092， China）Abstract Based on the orthogonal effect， the existing combination rules of multidimensional seismic response usually underestimate the responses of spatial structures，since the coupling effect of earthquake multicomponent is ignored. To address this issue，the limitations of the CQC rule and SRSS rule from conventional response spectrum applied in multidimensional conditions were pointed out. Thereafter，a multicomponent correlation coefficient was proposed and defined to quantify the correlation of multi-dimensional seismic components. Through extensive correlation analysis of earthquake records using parallel computing technique， the coefficient was proved to be rational and serviceable. On this basis， the coefficient was introduced into the SRSS rule and then the Multicomponent Correlated Combination （MCC） rule was put forward for the multidimensional seismic response of spatial structures. To validate the computational superiority of the MCC rule over the SRSS rule，a spherical latticed shell and a saddle latticed shell were employed for seismic evaluation by means of the pushover method and response history analysis method. The results show that the MCC rule provides more accurate prediction of multi-dimensional response than that by the SRSS rule，especially in terms of response distribution and variation tendency. Calculation errors for maximum displacement are generally less than 15%， which overcomes the drawback of underestimation of the SRSS rule. The MCC rule maintains high computational efficiency， and its application is simple and convenient. Keywords spatial structure， multidimensional earthquake， combination rule， correlation analysis收稿日期：2022-08-07基金项目：国家自然科学基金资助项目（51378379）*联系作者：曲扬，男，工学博士，一级注册结构工程师，一级注册建造师，高级工程师，研究方向为空间结构地震反应分析方法和施工过程模拟技术。
翻译(排序版)核专业英语~nuclear energy
A字开头A complete understanding of the microscopic structure of matter (物质微观结构) and the exact nature of the forces acting(作用力的准确性质) is yet to (有待于) be realized. However, excellent models have been developed to predict behavior to an adequate degree of accuracy for most practical purposes. These models are descriptive (描述的) or mathematical often based on analogy (类推) with large-scale process, on experimental data (实验数据), or on advanced theory.对物质的微观结构和作用力的准确性质的完全认识仍有待于实现。
然而，为了实际的用途，能足够精确地预知物质在微观世界行为的模型已经被研究出来。
这些模型是描述性的或数学的，基于对大尺度过程的类推、实验数据或先进的理论。
A nucleus can get rid of excess internal energy by the emission of a gamma ray, but in analternate process called internal conversion, the energy is imparted directly to one of the atomic electrons, ejecting it from the atom. In an inverse process called K-capture, the nucleus spontaneously absorbs one of its own orbital electrons. Each of these processes is followed by the production of X-rays as the inner shell vacancy is filled.一个原子核能够通过发射g 射线而除去过剩的内能，但在称为内转换的另一个交换过程中，能量直接传给原子中一个电子，使这一电子从原子中被逐出。
2013年四川芦山Ms7.0地震前的重力变化
２０日四ＪＩＩ芦山７．０级地震发生的关系．结果主要表明：①区域重力场异常变化与北东向龙门山断裂带南段和北北 西向马尔康断裂带在空间上关系密切，反映沿该两断裂带（段）在２０１０－－２０１２年期间发生了引起地表重力变化效
应的构造活动或变形．②芦山７．０级地震前，测区内出现了较大空间范围的区域性重力异常，而震源区附近产生了
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强震可能发生地点的判定，这在地震三要素预测中 尤为重要．因此，系统分析研究２０１３年四川芦山 Ｍｓ７．０地震前的重力场时空变化特征，对认识强震 的蕴育发生规律，捕捉地震前兆，开展强震中期预测 的应用研究具有现实意义． 本文拟利用川Ｉ西地区２０１０－－２０１２年期间的流 动重力观测资料，系统分析了区域重力场变化及其 与２０１３年４月２０ １３四川Ｉ芦山７．０级地震发生的
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拱坝抗震措施设计
摘要目前，拱坝已经被广泛应用于现代水利工程的高坝建设之中，因为拱坝相比其他类型大坝具有很多的优势，比如超载能力强、造型优美、抗震性能好、结构轻巧等优点。
本设计主要应用到有限单元法静动力分析的原理和计算方法，应用FEPG.GID 软件建立白鹤滩拱坝的实体模型，建立模型的过程发现该软件强大的建模功能，之后会用到功能全面的有限元软件ABAQUS，用此软件对白鹤滩拱坝进行有限元动力分析。
主要有以下的研究结论和工作内容：（1）动力计算分析时进行拱坝动力时程分析，通过计算与分析，研究白鹤滩拱坝在地震力作用下的动力响应特征。
动力时程分析结果显示，建设大坝设置扩大基础比无扩大基础更加的安全，有效的降低坝基的压应力，根据应力的分布，进行配筋设置。
根据损伤图提出相应的抗震措施。
（2）本设计是以工程实例为根据，应用ABAQUS软件进行静动力分析，最终得到位移应力图以及动力响应的结果特性良好，这些成果对实际工程设计及建设有实际的指导作用。
关键词：白鹤滩拱坝；建模；有限元动力分析计算；应力分析。
Design of Anti - seismic Measures for Arch DamIAbstractAt present, arch dams have been widely used in the construction of high dams of modern water conservancy projects, because arch dams have many advantages over other types of dams, such as overloading ability, beautiful shape, good seismic performance and light structure. Due to the complex spatial shell structure of the arch dam, the stress condition of the arch dam is also very complicated. The important index to evaluate the safety of an arch dam is the stress and strain performance of the dam, and the arch dam under complex stress Deformation and stress variation rules and characteristics of the high arch dam structure safety analysis and evaluation has very important significance and value.This design is mainly applied to the principle and calculation method of static and dynamic analysis of finite element method. The physical model of Baihetan arch dam is established by FEPG.GID software. Finite element software ABAQUS is used to analyze the finite element static and dynamic force of Baihetan arch dam. The main contents of the work and the conclusions are as follows:(1) Dynamic analysis of arch dams is carried out. The dynamic response characteristics of Baihetan arch dam under the action of seismic force are studied by calculation and analysis. The results of dynamic time history analysis show that the construction of dam foundation is more safe than non -expanding foundation, effectively reducing the compressive stress of dam foundation, and arranging reinforcement according to the distribution of stress. According to the damage map to put forward the corresponding seismic measures.(2) The design is based on the concrete high arch dam engineering example, using the large-scale finite element analysis software ABAQUS three-dimensional finite element analysis method to obtain the displacement diagram, stress diagram, structure of the vibration characteristics and dynamic response results regularity is better, These results not only have practical effect on the construction and design of practical projects, but also have great reference value for similar projects.Key words:Baihetan arch dam; modeling; finite element dynamic analysis and calculation; stress analysis。
震级大小和传播距离对相干函数的影响
第32卷第2期苏州科技大学学报(工程技术版)Vol.32No.2 2019年6月Journal of Suzhou University of Science and Technology(Engineering and Technology)Jun.2019震级大小和传播距离对相干函数的影响尚静1,丁海平12（1.苏州科技大学江苏省结构工程重点实验室，江苏苏州215011；2.中国地震局工程力学研究所,黑龙江哈尔滨150080）摘要：根据我国台湾SMART-1台阵采集的3次不同震级和震源距的地震加速度记录,分别计算了台站间距d等于200,400,800J000和2000m的相干系数,并采用L0H和Ahrahamson提出的相干函数模型对相干系数进行了拟合,对比结果表明：（1）震级大小对地震动相干性影响较大，震级小的相干性较好；（2）地震波的传播距离对地震动的相干性影响不显著，震源距较小地震的地震动相干性较小。
并针对地震动相干函数中的只包含台站间距和频率2个参数的情况，建议在今后的研究中，相干函数表达式应该尽可能考虑地震震级和传播距离的影响。
关键词：相干函数;地震震级;传播距离；曲线拟合中图分类号：P315.3文献标识码：A文章编号：2096-3270（2019）02-0026-06地震动的空间变化闪是指在地震波的传播过程中，不同的两个场点（即便距离很近）的地震动会表现出不同的运动状态和特征，即两场点的振幅和相位存在差异，这种地震动的空间变化对桥梁、管道和大坝等大跨度结构的抗震分析和设计有很大影响。
造成地震动空间变化的因素很多，如Somerville等卩勺将地震动空间变化归结为两个方面:一是震源，二是传播途径和场地;Kiureghian^］认为地震动空间变化受四个因素影响，即行波效应、非相干效应、衰减效应和场地效应;Abrahamson^用图形形象地解释了影响地震动空间变化的4个因素:地震波传播、震源破裂过程、散射和衰减。
介绍地震的英语作文
介绍地震的英语作文Earthquakes are a natural phenomenon that occurs when theEarth's tectonic plates shift, causing seismic waves that can result in significant destruction. They are measured usingthe Richter scale, which quantifies the magnitude of an earthquake based on the amplitude of the seismic waves.Earthquakes happen most frequently along the boundaries of tectonic plates, where the Earth's crust is most active. The Pacific Ring of Fire, which encircles the Pacific Ocean, is one of the most seismically active areas on the planet. However, earthquakes can occur anywhere, even in regions not typically associated with seismic activity.The effects of an earthquake can be devastating. Buildingscan collapse, roads can be cracked, and the ground can be shaken violently. In addition to the immediate damage, earthquakes can also trigger secondary disasters such as tsunamis, landslides, and fires.Preparation and response are crucial for minimizing theimpact of earthquakes. This includes having an emergency plan, securing furniture to walls, and having a supply kit ready.In the event of an earthquake, it's advised to drop to the ground, take cover under a sturdy piece of furniture, andhold on until the shaking stops.Scientists continue to study earthquakes to better understandtheir causes and to develop more effective ways to predict and mitigate their effects. Advances in technology, such as seismographs and satellite imagery, have greatly improved our ability to monitor seismic activity and issue warnings.In conclusion, while earthquakes are a natural and inevitable part of our planet's geological processes, understanding and preparing for them can save lives and reduce the damage they cause. It is important for communities to be educated on earthquake safety and for governments to invest in infrastructure that can withstand seismic events.。
关于地震的英语作文模板
关于地震的英语作文模板英文回答：Earthquakes are a natural phenomenon that can cause widespread destruction and loss of life. They occur when there is a sudden release of energy below the Earth's surface, causing the ground to shake violently. Earthquakes can be caused by a variety of factors, including:Tectonic plate movement: When tectonic plates collide, they can cause the ground to shake. This is the most common cause of earthquakes.Volcanic activity: Earthquakes can also be caused by volcanic eruptions. When magma moves beneath the Earth's surface, it can put pressure on the surrounding rocks, causing them to crack and shift.Fault lines: Earthquakes can also occur along fault lines. Fault lines are cracks in the Earth's crust wheretectonic plates meet. When the plates move past each other, they can cause the ground to shake.The magnitude of an earthquake is measured on the Richter scale. The Richter scale is a logarithmic scale, so each whole number increase in magnitude represents atenfold increase in the amplitude of the seismic waves. Earthquakes with a magnitude of 7.0 or greater are considered to be major earthquakes.Earthquakes can cause a variety of hazards, including:Ground shaking: The ground shaking caused by an earthquake can damage buildings, bridges, and other structures. It can also cause landslides and avalanches.Liquefaction: Liquefaction occurs when the ground becomes saturated with water and loses its strength. This can cause buildings to sink and roads to buckle.Tsunamis: Tsunamis are large waves that are generated by earthquakes. They can travel across oceans and causewidespread damage.Earthquakes can be very dangerous, but there are things that you can do to protect yourself:Be aware of the earthquake hazards in your area.Make an earthquake preparedness plan.Have an earthquake kit that includes food, water,first-aid supplies, and other essential items.Drop, cover, and hold on when an earthquake occurs.中文回答：地震是一种自然现象，可以造成广泛的破坏和人员伤亡。
高中英语作文地震
高中英语作文地震Earthquakes: A Call for Preparedness and ResilienceIn the vast tapestry of natural phenomena, earthquakes stand as one of the most powerful and unpredictable forces that can reshape the landscape and challenge the resilience of communities. An earthquake is the sudden shaking of theEarth's surface caused by the rapid release of energy in the Earth's crust that creates seismic waves. These seismic waves can cause widespread destruction, from collapsing buildings to triggering tsunamis.The unpredictability of earthquakes makes it essential for communities to be well-prepared. Preparedness involves several aspects, including education about earthquake safety, the development of emergency plans, and the construction of buildings that can withstand seismic activity. Schools play a crucial role in educating students about the importance of earthquake preparedness. Students are taught to "Drop, Cover, and Hold On" during an earthquake, which involves dropping to the ground, taking cover under a sturdy piece of furniture, and holding on until the shaking stops.Beyond immediate safety measures, communities must also focus on long-term resilience. This includes the development of infrastructure that can withstand earthquakes, such as buildings designed to flex rather than break under the stress of seismic waves. Governments and organizations often worktogether to create building codes and standards that aim to minimize the damage caused by earthquakes.In addition to infrastructure, communities must also develop robust response and recovery plans. This includes having trained emergency responders, clear communication channels, and resources in place to assist those affected by an earthquake. The aftermath of an earthquake can be chaotic, and having a well-organized plan can save lives and speed up the recovery process.However, the impact of an earthquake is not just physical; it also has profound psychological effects on those who experience it. The trauma of an earthquake can lead to feelings of fear, anxiety, and helplessness. It is important for communities to provide support and resources to help individuals cope with the emotional aftermath of such a disaster.In conclusion, earthquakes are a force of nature that demand our respect and preparedness. By educating our communities, building resilient infrastructure, and developing comprehensive response plans, we can mitigate the impact of earthquakes and foster a sense of resilience in the face of these powerful events. As we continue to learn more about earthquakes and how to prepare for them, we can build a safer and more resilient future for all.。
地震英语作文高级
地震英语作文高级Earthquakes: A Natural Phenomenon with Profound ImpactIn the grand tapestry of natural phenomena, earthquakes stand out as a force of nature that can reshape landscapes andalter the course of human history. The seismic waves that emanate from the heart of our planet are a reminder of the immense power that lies beneath our feet. This essay delves into the science behind earthquakes, their impact on society, and the measures taken to mitigate their effects.Understanding EarthquakesAn earthquake is the result of sudden release of energy in the Earth's crust that creates seismic waves. These waves are caused by the movement of tectonic plates, which are massive slabs of solid rock that make up the Earth's surface. The boundaries where these plates meet are zones of intense geological activity, often leading to earthquakes. There are three primary types of plate movements that can cause earthquakes: convergent boundaries where plates move towards each other, divergent boundaries where plates move apart, and transform boundaries where plates slide past each other.The Science of Seismic ActivitySeismologists, the scientists who study earthquakes, have developed sophisticated instruments to measure and monitorseismic activity. Seismographs record the vibrations caused by earthquakes, allowing researchers to determine the location, depth, and magnitude of the event. The Richter scale is commonly used to quantify the energy released by an earthquake, with each whole number increase representing a tenfold increase in amplitude.Impact on SocietyThe impact of earthquakes can be catastrophic. They can lead to the collapse of buildings, disruption of infrastructure, and loss of life. The 2004 Indian Ocean earthquake and tsunami, and the 2010 Haiti earthquake are stark reminders of the devastation that can occur. However, the effects of an earthquake are not limited to the immediate aftermath. Long-term consequences include economic downturns, displacement of populations, and psychological trauma.Preparation and MitigationGiven the potential for widespread destruction, it is crucial to prepare for and mitigate the effects of earthquakes. Building codes that incorporate seismic-resistant designs are essential in earthquake-prone regions. Early warning systems, which can provide precious seconds or minutes of warning before the ground starts to shake, are also critical. Furthermore, public education campaigns can ensure that communities are aware of what to do during an earthquake, such as the "Drop, Cover, and Hold On" protocol.ConclusionEarthquakes are a testament to the dynamic and powerful forces at work within our planet. While they can bring about significant destruction and loss, they also inspire innovation in the fields of seismology and civil engineering. As our understanding of these natural events grows, so too does our ability to prepare for and respond to them, offering hope for a safer future in the face of this formidable force of nature.。
考虑地层空间变异性的岩溶区基础可靠度分析
第49卷第7期2022年7月Vol.49，No.7Jul.2022湖南大学学报（自然科学版）Journal of Hunan University（Natural Sciences）考虑地层空间变异性的岩溶区基础可靠度分析吴高桥†，聂建国（清华大学土木工程系，北京100084）摘要：基于随机场理论和Karhunen-Loeve展开构造随机场以模拟具有空间变异性的地层，并结合有限元极限分析法和蒙特卡洛模拟对含溶洞地层上的基础开展可靠度分析.本文重点是通过大量数值模拟进行全面参数分析，探究地层中溶洞特征（如溶洞埋深、溶洞水平偏移距离）以及土体空间变异性参数（如土体相关长度、土体变异系数）对基础极限承载力以及失效概率的影响；进而结合可视化溶洞-基础体系破坏模式深入揭示岩溶区基础失效概率变化机理；最后将有限元极限分析结果与已有研究进行对比，验证了数值模型的准确性及研究结论的可靠性.结果表明体系破坏线发散度越大，则基础在受荷破坏时可能发展出的破坏路径越多，从而导致失效概率提高；此外，下伏溶洞距基础越远或土体空间变异性越强则基础失效概率越高，且失效概率将随所选取安全系数的增加而大幅降低.在前期设计中若采用本文方法进行可靠度分析，为确保安全性，安全系数应尽量大于2并采用下限理论进行分析.关键词：基础工程；溶洞；有限元极限分析；随机场理论；随机分析中图分类号：U416.161文献标志码：AReliability Analysis of Footings Lying on Karst AreaConsidering Spatially Variability of StratumWU Gaoqiao†，NIE Jianguo（Department of Civil Engineering，Tsinghua University，Beijing100084，China）Abstract：This study simulates the soils with spatial variability by random field theory and Karhunen-Loeve ex⁃pansion.Reliability analysis of strip footing lying on karst area is carried out based on finite element limit analysis and Monte Carlo simulation.The emphasis of this study is performing the parametric analysis through finite element modeling，in order to explore the effect of karst cave parameters（including depth and horizontal offset distance of karst caves）and spatial variability parameters（including correlation length and coefficient of variation）on the ulti⁃mate bearing capacity and failure probability of footings.Then，combined with the visualization of failure patterns of cave-footing system，the variation mechanism of footing failure probability is revealed.Finally，the finite element analysis results are compared with the existing research results to verify the accuracy of the numerical model and the reliability of the research conclusions.The results indicate that the higher the disperse degree of failure curve is，the more failure paths may develop under external loads，which leads to a higher failure probability of the footing.Fur⁃thermore，the footing failure probability increases with the increase of distance between the karst cave and the foot⁃∗收稿日期：2022-03-11基金项目：清华大学水木学者计划（2021SM007），Shuimu Tsinghua Scholar Project of Tsinghua University（2021SM007）作者简介：吴高桥（1993—），男，湖南邵阳人，清华大学助理研究员，博士†通信联系人，E-mail：文章编号：1674-2974（2022）07-0045-09DOI：10.16339/ki.hdxbzkb.2022070湖南大学学报（自然科学版）2022年ing.The higher spatially variability of soils also leads to a higher failure probability of the footing.And the failure probability decreases significantly with the increasing factor of safety.If the method proposed in this paper is used for reliability analysis in the advanced design，the safety factor should be larger than2as far as possible and the lower limit theory should be used for analysis，in order to guarantee the safety.Key words：foundation engineering；Karst cave；finite element limit analysis；random field theory；stochastic analysis我国喀斯特地貌占地约344万平方千米，广泛分布于我国西部地区.随着近年城市化进程加速，土地紧缺问题日益严重，因此越来越多建筑将无可避免地选址在岩溶发育地区.然而近年来，因地层中空洞失稳引起的上部构筑物沉降和倾斜等灾害时有发生，据2020年中央级媒体、部委网站、公开出版物、中央重点新闻网站及地方重点报网等报道的数据，2020年地下空洞相关灾害与事故共237起，数量与2019年持平［1］，造成巨大的人员伤亡和经济损失.因此，对含溶洞地层上基础的可靠性进行分析，将有利于上部构筑物的安全性，并为上部施工提供指导，具备重要理论意义和实际工程价值.国内外有众多学者通过理论分析、模型试验和数值模拟等手段针对空洞-基础体系稳定性开展研究.在理论分析方面，Wang和Hsieh［2］基于传统上限分析法研究了圆形空洞正上方条形基础的稳定性问题，提出基础稳定性理论计算框架和基础极限承载力计算公式，并总结3种典型破坏模式.随后Wang 等［3］继续研究了空洞与条形基础水平距离对体系破坏模式的影响，将典型破坏模式扩展至10种，并归纳了不同破坏模式之间的演化规律.刘辉等［4］通过极限分析上限法合理构造速度场，进而通过剪切耗散和基础功率的关系推出溶洞上方条形基础的极限承载力计算方法，并详细分析了不同参数对体系破坏模式的影响.赵明华等［5］考虑自然溶洞形成过程中溶洞顶板的空间形态特征，采用结构力学分析理论建立了溶洞顶板最小抗弯厚度的计算公式，并揭示了该厚度随空洞跨度、地层物理力学性质以及基础所受荷载改变而变化的规律.在模型试验方面，Wood等［6］和Al-Tabbaa等［7］基于模型试验分析了下伏空洞对上部浅基础承载力的削弱作用.Kiyosumi 等［8］研究了溶洞-基础体系的稳定性问题，通过对基础失去承载能力后溶洞周边岩体的破坏情况，总结了多溶洞工况下，不同排布位置的溶洞对上部基础极限承载力的影响.刘铁雄等［9］和王革立［10］将溶洞上方地层视为梁板，通过一系列试验分析了溶洞跨径、溶洞上覆岩土体厚度等对基础稳定性的影响.赵明华等［11］通过模型试验，研究了上部基础荷载作用下的岩溶顶板的承载机理，对诸如顶板厚跨比、地层力学性能等参数开展了参数分析，并总结了溶洞安全埋深的计算公式.上述研究使研究工程人员对空洞-基础稳定性问题有了更深入的认知，但使用理论分析时，通常要事先对问题进行一定假设以降低求解难度，因此仅能分析相对简单的问题.而模型试验受限于时间成本和经济成本，无法开展大规模研究以进行参数分析.随着计算机算力的发展，数值模拟成为了一种被广泛使用的岩土工程分析方法.Baus和Wang［12］在1983年采用有限元法（finite element method，FEM）研究了粉质黏土中空洞上方条形基础的稳定性问题，并总结出能够反映空洞尺寸、空洞位置及条形基础埋深对基础极限承载力影响的设计图.Badie和Wang［13］采用三维有限元程序对基础-空洞体系稳定性进行分析，结果表明基础下方存在某临界区域，只有当下伏空洞处于该区域范围内时空洞才会对基础造成显著影响，且该临界区域的范围取决于土体物理力学性质以及空洞大小和位置.Jao等［14］使用有限元法研究了条形基础荷载作用下的有衬砌隧道稳定性问题，对不同地层类型、隧道大小、隧道位置以及衬砌厚度的影响进行了详细探讨.孙映霞等［15］采用有限差分法（finite difference method，FDM）研究下伏空洞埋深以及距基础距离对体系失稳机理的影响.随后在其基础上，Kiyosumi等［16］使用有限元软件PLAXIS率先对多空洞上方条形基础的极限承载力进行研究，分析了不同位置空洞对基础造成影响强弱的关系，结果表明靠近基础的空洞对基础承载力造成的影响远大于较远处空洞.基于Kiyosumi的研究，Lavasan等［17］分析了位于两个平行圆形空洞上方的条形基础的极限承载力，深入研究了空洞的破坏机理并归纳了数种典型破坏模式.随后Zhou等［18］和46第7期吴高桥等：考虑地层空间变异性的岩溶区基础可靠度分析Lee 等［19］分别采用局部不连续优化法（discontinuitylayout optimization ，DLO ）和有限元法分析了下伏双空洞对条形基础稳定性的影响.上述研究基本全部假设空洞所处地层为均匀材质，然而现实中地层往往具有一定的空间变异性，这将导致基础承载机理发生改变，进而增加基础承载力的不确定性，因此有必要在基础稳定性分析中充分考虑土体空间变异性的影响.鉴于此，本研究结合随机场理论和Karhunen-Loeve 展开构造实现随机场土体强度的随机分布，进而通过有限元极限分析和蒙特卡洛模拟（Monte Carlo simulation ）对含溶洞地层上基础进行可靠度分析，着重分析下伏溶洞位置及土体空间变异程度对基础稳定性及失效概率的影响，以期为工程设计提供参考，并进一步确保岩溶区基础的安全性.1问题描述1.1基本假定图1为待研究问题的平面模型示意图，问题关键影响因素已标示于图中.具体为：地表存在宽度为D 的条形基础，在其中心位置施加有竖直集中荷载q u .基础下方地层存在边长为D 的正方形溶洞，溶洞中心到地表及基础中垂线的垂直距离分别为H 和S .空洞周围的土体遵循特雷斯卡屈服准则（Tresca yield criterion ）且存在一定空间变异性，其重度γ=20kN/m 3，平均剪切强度s u =40kPa.条形基础q uD15DSHD30D空间变异性土体γ=20kN/m 3Mean of s u =40kPa图1平面模型示意图Fig.1Sketch of plain strain model1.2数值模型建立为了尽量规避边界效应，需要建立尺寸足够大的数值模型，以保证在所有工况中塑性破坏区不会延伸至模型的侧面边界以及下边界.经测试，当模型尺寸宽度为30D 、高度为15D 时既可满足上述要求，也能保证较高的运算效率.此外，基于已有研究［19-21］，本文在模型底部边界设置完全约束，左右两侧边界设置水平约束，在地表边界则不设置约束.由于本文拟采用蒙特卡洛法分析基础失效概率，所以对每组工况均需开展上千次模拟以获得准确结果，这将耗费大量时间.因此为了尽可能提高分析效率和精度，采用网格自适应迭代技术基于分析域内能量耗散情况对网格进行重分布优化.针对本文数值模型，将网格初始数量和最终数量分别设置为1000和10000，自适应迭代次数设为3次，经过重分布优化后的效果图如图2所示.图2网格自适应分布效果图Fig.2Sketch of mesh re-arrangement1.3随机场实现本文假定地层土体遵循Tresca 屈服准则，其中对基础稳定性影响最大的参数为不排水剪切强度s u ，因此在本文的随机分析中主要考虑土体剪切强度的空间变异性.为实现土体空间变异性，将土体不排水剪切强度在分析域内模拟为对数正态分布，其具体表达式为：f (x )=1xσln x 2πexp éëêêêê-12(ln x -μln x σ2ln x )2ùûúúúú（1）剪切强度的均值和标准差可以通过一种能简洁描述随机场土壤固有变异性的无量纲变异系数（co⁃efficient of variation ，COV ）表示.该参数能够帮助设计者对土体中固有变异性的可能范围进行评估［22］，具体表达式为：COV =Standard deviationMean（2）上述表达式中的对数正态分布参数可表示47湖南大学学报（自然科学版）2022年如下：σln x =ln ()1+COV 2（3）μln x =ln μx -12σ2ln x （4）对式（3）和式（4）进行转换可得：μx =exp (μln x +12σln x 2)（5）σx =μx exp ()σln x 2-1（6）则对数正态分布的累积分布函数（cumulativedistribution function ，CDF ）可表示为：CDF =12erfc (-ln x -μln x σln x 2)（7）式中：erfc 为互补误差函数.需要注意的是，CDF 是随机分析中概率密度函数（probability density function ，PDF ）的积分形式.除了上述对数正态分布参数，还有两个重要参数在随机场理论中至关重要，即用于描述空间变异性土体不同方向波动程度的水平相关长度（CL x ）以及垂直相关长度（CL y ）.相关长度被定义为土体中一临界距离，若土体中任意两点间距离小于该距离，则两点的剪切强度趋于密切相关，且相关长度越大则随机场中剪切强度的过渡越平滑；相反，相关长度越小则土体中各点剪切强度的关联性越弱，随机场趋于参差.由其定义可知当相关长度趋于无穷大时，分析域可视为均匀土体；而当其趋于0时，随机场中各点之间无任何关联.为了更直观地反映相关长度与随机场平滑度的关系，将水平、竖直相关长度不同的土体剪切强度分布模拟情况列于图3.对比图3（a ）和图3（b ）可以看出，当竖直相关长度较大时，土体剪切强度在竖直方向过渡较均匀；而当水平相关长度较大时，则土体剪切强度在水平方向过渡较均匀.由图3（c ）可知若各向相关长度均较小，土体的剪切强度分布较离散且无规律.Phoon 和Kulhawy ［22］经过大量调研总结出土体在水平方向的随机性通常较弱，CL x 范围在46m 到60m 之间；而土体在竖直方向的随机性通常较强，CL y 的范围在0.8m 到6.1m 之间.基于上述结论，本文中的CL x 固定为50m ，仅考虑CL y 对基础稳定性的影响.为了方便表述，对相关长度进行无量纲化处理如下：Θx =CL x /D （8）Θy =CL y /D（9）（a ）Θx =1，Θy =50（b ）Θx =50，Θy =1（c ）Θx =1，Θy =1（d ）Θx =50，Θy =50图3不同相关长度对应的土体剪切强度分布云图Fig.3Shear strength distribution of soil domainwith different correlation lengths本研究选择通过能够提供指数协方差函数解析解的Karhunen-Loeve 展开式生成随机场.由于该展开式的项数将随着随机场相关长度的减小而大幅增加［23］，因此为了保证随机分析结果的可靠度，将展开项数设置为1000.此外，本研究采用蒙特卡洛模拟分析基础失效概率，若模拟次数不足，将严重影响所得结果的准确性，因此在后续随机分析中各工况模拟次数均设为500次.2确定分析通过随机分析研究基础失效概率问题的原理是先不考虑土体空间变异性，对各工况进行传统确定分析（deterministic analysis ）；随后再通过多次模拟随机场并总结小于经安全系数换算过的确定性分析基础承载力的次数，进而得出基础失效概率.则失效概率的表达式为：p f =p (N ram ≤N det FS)（10）式中：p f 为基础失效概率，在本文中具体定义为500次蒙特卡洛模拟所得极限承载力中小于确定性承载力N det 与安全系数比值的比例；FS 为设计中选取的安全系数（factor of safety ），一般来说安全系数越大，则设计越保守；N ram 为每次蒙特卡洛模拟所得基础极限承载力因子；N det 为确定分析中的基础极限承载力因子，其具体定义为：N det =q us u（11）式中：q u 为基础极限承载力；s u 为土体剪切强度.基础极限承载力与下伏空洞所处位置密切相关，参照已有研究，在本节中对H /D =1、2、3、4以及48第7期吴高桥等：考虑地层空间变异性的岩溶区基础可靠度分析S /D =0、0.5、1、2、3、4对应的工况进行确定分析，所得结果为上限解及下限解的平均值，基础极限承载力因子总结于图4以及表1.由图4可知基础极限承载力将随着S /D 以及H /D 的增加而提升，这是因为下伏溶洞离基础越远，则其对基础造成的负面影响越弱.同时，H /D 越大则对应的承载力曲线越平缓，这说明溶洞埋深越大则水平位置的改变对基础的影响越弱.此外，图4中有多个工况基础极限承载力因子集中在5.20附近，该现象说明此时溶洞由于距离过远不再对基础产生影响.6543210N d e t1234H /D =1H /D =2H /D =3H /D =4S /D图4不同H /D 条件下S /D 对N det 的影响Fig.4Effect of S /D on N det with different H /D表1H /D 和S /D 对N det 的影响Tab.1Effect of H /D and S /D on N detH /D 1234N detS /N =00.822.363.854.76S /N =0.51.392.653.954.77S /N =12.243.184.124.81S /N =23.754.204.755.195S /N =34.755.205.205.20S /N =45.215.205.205.213随机分析本节将基于确定性分析结果开展随机分析，以期全面探究空洞埋深、空洞水平偏移距离以及土体竖直相关长度对基础平均承载力因子以及失效概率的影响.其中基础平均承载力因子为每个工况500次蒙特卡洛模拟所得极限承载力因子的平均值.由于随机分析中每个工况均需构造500个不同的随机场并计算相应的基础极限承载力，导致运算量巨大，因此对所有影响因素进行排列组合再开展全面分析是不现实的.鉴于此，本文参考正交试验设计原理，在探究某些参数的影响时固定其他参数，以达到减少运算量且不影响所得规律的目的.本文随机分析所考虑工况的具体参数见表2.表2待研究影响因素Tab.2Influential factors to be investigated固定参数变异系数水平相关长度溶洞边长土体重度平均剪切强度蒙特卡洛模拟次数网格数量自适应迭代次数变动参数溶洞埋深溶洞水平偏移距离垂直相关长度安全系数参数值COV=25%Θx =50D =1m γ=20kN/m 3μsu =40kPa 500100003参数值H /D =1，2，3，4（S /D =0，Θy =1）S /D =0.5，1，2，3，4（H /D =2，Θy =1）Θy =0.125，0.25，0.5，1，2，4（H /D =2，S /D =0）FS=1，1.2，1.5，23.1空洞埋深的影响为了探究空洞埋深对基础稳定性的影响，对S /D =0，Θy =1以及H /D =1，2，3，4对应工况开展蒙特卡洛模拟，所得基础平均极限承载力因子和失效概率分别总结于图5和图6.由图5可以看出随机分析所得的平均承载力因子变化趋势基本和确定分析一致，但由于土体存在空间变异性，导致蒙特卡洛模拟所得的大部分基础极限承载力因子小于确定分析，所以平均承载力因子会小于确定分析所得结果.543210μN 1.01.52.02.53.03.54.0确定分析（均值）随机分析（上限）随机分析（下限）H /D图5S /D =0，Θy =1，COV=25%时H /D 对μN ram 的影响Fig.5Effect of H /D on μN ram with S /D =0，Θy =1，COV=25%49湖南大学学报（自然科学版）2022年1.00.90.80.70.60.50.40.30.20.10p f1.01.52.02.53.03.54.0FS=1（上限）FS=1.2（上限）FS=1.5（上限）FS=2（上限）FS=1（下限）FS=1.2（下限）FS=1.5（下限）FS=2（下限）H /D图6S /D =0，Θy =1，COV=25%时H /D 对p f 的影响Fig.6Effect of H /D on p f with S /D =0，Θy =1，COV=25%图6为各工况通过上、下限分析所得的基础失效概率.可以看到对几乎所有工况而言，基础失效概率都随空洞埋深的增加而增加，该结论似乎与实际情况不符，因为通常认为下伏溶洞距离基础越远则其对基础承载能力造成的负面影响越小.实际上确如图5所示，基础的极限承载力因子随着H /D 的增加而单调增加.但本文中的失效概率是指采用确定分析所得基础极限承载力进行设计时，由土体空间变异性引起失稳的概率，与基础极限承载力的绝对大小无必然联系.值得一提的是，在实际工程设计中一般会通过增加安全系数的方式以保证安全性，因此有必要在失效概率分析中考虑安全系数的影响.由图6可以看出随着安全系数的增加，基础失效概率显著下降，当安全系数为2时基础的失效概率将趋于0，同时由曲线上升幅度可知安全系数越小则空洞埋深对基础失效概率的影响越显著.此外，通过对比上、下限分析对应的失效概率，可以看出使用上限分析进行蒙特卡洛模拟时所得基础失效概率较低.为了进一步探究基础失效概率变化机理，将某次蒙特卡洛模拟所得溶洞-基础体系破坏模式总结于图7，可以看出当空洞埋深较浅时，破坏线较集中，说明体系的破坏模式较单一.而随着溶洞埋深的增加，主破坏线逐渐向周围发散且发散程度越来越明显，而这些较为发散的破坏线可能导致土体中失稳路径（fail⁃ure path ）增加，进而引起破坏模式的复杂化并导致失效概率的增加.3.2空洞水平偏移距离的影响为了探究空洞水平偏移距离的影响，将H /D =2，Θy =1以及S /D =0.5，1，2，3，4工况对应的平均承载力因子和基础失效概率总结于图8和图9.由图8可以看出随机分析所得的平均承载力因子变化趋势与确定分析基本一致，这与图5所展示的规律基本一致.由此可以认为只要蒙特卡洛模拟次数达到一定数量，那么土体空间变异性几乎不会对随机分析中的平均承载力因子变化趋势造成影响.（a ）H /D =1（b ）H /D=2（c ）H /D =3（d ）H /D =4图7S /D =0，Θy =1，COV =25%时H /D 对体系破坏模式的影响Fig.7Effect of H /D on failure pattern withS /D =0，Θy =1，COV =25%确定分析（均值）随机分析（上限）随机分析（下限）μN 5.55.04.54.03.53.02.52.01234S /D图8H /D =2，Θy =1，COV=25%时S /D 对μN ram 的影响Fig.8Effect of S /D on μN ram with H /D =2，Θy =1，COV=25%从图9可看出除FS=1的下限分析以及FS=1.5的上限分析在S /D =0时失效概率略高于S /D =0.5，其余工况的基础失效概率随溶洞水平偏移距离的增加而增加.图10为各工况对应的体系破坏模式，可以看出当溶洞水平偏移距离较小时，破坏主要集中在洞顶，且破坏线较细.随着空洞偏移距离的持续增加，破坏模式逐渐变为洞顶-洞侧联合破坏，且溶洞顶部50第7期吴高桥等：考虑地层空间变异性的岩溶区基础可靠度分析将受到来自其正上方土体的挤压.此外可以看到S /D =0和S /D =0.5时破坏线离散度较低，因此其所对应的失效概率接近.而随着溶洞水平偏移距离的增加，破坏线发散程度加剧进而导致基础受荷时土体中可能发展出的失稳路径增多，引起失效概率的增加，这与图9所展示的规律相吻合.结合3.1与3.2节的研究，可以认为对大部分工况而言，除了溶洞水平偏移距离极小的工况，下伏溶洞与基础的间距（包括埋深及水平偏移距离）越大，则对应的基础失效概率越高.此外结合图6和图9可知采用极限分析下限法进行随机分析时，所得基础失效概率相对于上限法明显偏高，而承载力偏低，亦即采用下限法进行施工设计时总体偏于保守.FS=1（上限）FS=1.2（上限）FS=1.5（上限）FS=2（上限）FS=1（下限）FS=1.2（下限）FS=1.5（下限）FS=2（下限）1.00.90.80.70.60.50.40.30.20.10p f-0.50.51.01.52.02.53.03.54.04.5S /D图9H /D =2，Θy =1，COV=25%时S /D 对p f 的影响Fig.9Effect of S /D on P f with H /D =2，Θy =1，COV=25%（a ）S /D =0（b ）S /D=0.5（c ）S /D =1（d ）S /D=2（e ）S /D =3（f ）S /D =4图10H /D =2，Θy =1，COV=25%时S /D 对体系破坏模式的影响Fig.10Effect of S /D on failure patternwith H /D =2，Θy =1，COV=25% 3.3土体空间变异性参数的影响为了探究土体空间变异性参数对基础稳定性的影响，在本节对H /D =2、S /D =1时不同Θy 和COV 对应的基础平均承载力因子和失效概率进行分析.由图11可知基础平均承载力因子随竖直相关长度的增加而单调递增，这是因为土体强度相关性越高则地层中剪切强度的过渡更平滑，从而使得由于土体强度分布不均导致的极低承载力工况数量减少.且承载力增强速度将逐渐平缓，当Θy =4时平均承载力因子已与确定性分析所得结果（图中水平虚线所示）相差无几，这说明此时土体空间变异性的影响较弱，已趋近于均质土.此外，COV 越大则平均承载力越低，这是因为土体变异系数越大则土体空间变异性越强，这将导致蒙特卡洛模拟中低承载力工况数量的增多，进而引起平均承载力因子的下降.0.51.01.52.02.53.03.54.04.5μN 3.23.02.82.62.42.22.01.8N det =3.18COV=25%（上限）COV=25%（下限）COV=60%（上限）COV=60%（下限）Θy图11H /D =2，S /D =1时Θy 对μN ram 的影响Fig.11Effect of Θy on μN ram with H /D =2，S /D =1图12为Θy 和COV 对基础失效概率的影响.可以看到失效概率随Θy 的增加而单调递减，且当Θy 很小时，失效概率相对很高，此时Θy 只需略作提高则基础失效概率将大幅降低，而随着Θy 的进一步增加，失效概率的降低速度减缓.结合上文所得结论，可知空间变异性较强时，空间变异性参数对基础承载力以及失效概率的影响较显著，而当空间变异性较弱时，空间变异性参数的改变仅对基础产生微弱影响.图13为不同Θy 和COV 对应的破坏模式图.对比图13（a ）（c ）（e ）（g ）和图13（b ）（d ）（f ）（h ）可以看到当Θy 较小时，破坏线的离散度很高，因此所对应的基础失效概率很高；而当Θy 从2增加到4时，体系破坏模式及破坏线几乎没有变化，说明此时基础失效概率趋于稳定，与图12所示规律相吻合.而对比COV=51湖南大学学报（自然科学版）2022年25%（左侧纵列）和COV=60%（右侧纵列）对应的破坏模式，可以看出COV=60%对应的地层空间变异性强度明显高于COV=25%时.以图13（b ）为例，在基础和溶洞间的主要破坏线之外还发育有多条破坏路径，这将导致基础失效概率剧增及承载力下降，因此COV 越大则基础失效概率越高，平均承载力因子越低，与图11和图12所示规律一致.FS=1，COV=25%FS=1.2，COV=25%FS=1.5，COV=25%FS=2，COV=25%FS=1，COV=60%FS=1.2，COV=60%FS=1.5，COV=60%FS=2，COV=60%1.00.90.80.70.60.50.40.30.20.10p f0.51.01.52.02.53.03.54.04.5Θy图12H /D =2，S /D =1时ΘY 对p f 的影响Fig.12Effect of Θy on p f with H /D =2，S /D=1（a ）Θy =0.125，COV=25%（b ）Θy =0.125，COV=60%（c ）Θy =0.5，COV=25%（d ）Θy =0.5，COV=60%（e ）Θy =2，COV=25%（f ）Θy =2，COV=60%（g ）Θy =4，COV=25%（h ）Θy =4，COV=60%图13H /D =2，S /D =1时Θy 和COV 对体系破坏模式的影响Fig.13Effect of Θy and COV on failure patternwith H /D =2，S /D =14模型验证为了验证有限元极限分析模型的可靠性，将本文确定分析的结果与已有有限元法［19］和不连续局部优化法结果［18］进行对比，如图14所示.通过对比可以发现本文上限分析结果略高于已有研究结果，下限分析结果则略低于已有研究结果，但总体变化趋势基本吻合，且最大误差小于5%.此外，有限元极限分析的真值是介于上、下限分析结果之间的，因此可以认为本文数值模型所得结果是准确可靠的.N d e t5.55.04.54.03.53.02.52.01.51.52.02.53.03.54.04.5本研究（上限）Lee 等[19]Zhou 等[18]本研究（下限）S /D =0，s u =300kPaH /D 图14本研究结果与不同数值方法结果对比Fig.14Comparisons between the present results andresults from other numerical methods5结论本文通过随机场理论和Karhunen-Loeve 展开的方式构建随机场，对岩溶发育地层上基础开展了一系列随机分析.采用有限元极限分析法以及蒙特卡洛模拟全面探究了溶洞埋深、溶洞水平偏移距离、土体相关长度以及土体变异系数对基础稳定性以及失效概率的影响，并结合可视化体系破坏模式深入分析基础失效概率变化机理.本研究所得结论如下：1）在随机分析中，若蒙特卡洛模拟样本数足够，则随机分析所得基础承载力变化趋势与确定分析所得趋势几乎一致；2）基础的承载力将随溶洞埋深、溶洞偏移距离、土体相关长度的增大以及土体变异系数的减小而提升，且上述参数较小时对基础的影响更显著；3）溶洞与基础的间距越远，则基础的失效概率越高.且基础的失效概率随土体相关长度的增大而降低、随土体变异系数的增大而升高；52。
地震的不同表达英语作文
地震的不同表达英语作文Title: Understanding Earthquakes: Different Expressions and Impacts。
Earthquakes are natural phenomena that occur when there is a sudden release of energy in the Earth's crust, resulting in seismic waves. These seismic events vary in intensity, magnitude, and impact, leading to different expressions and consequences. In this essay, we will delve into the diverse manifestations of earthquakes and their implications.Firstly, earthquakes can be categorized based on their magnitude, which is a measure of the energy released at the earthquake's source. The Richter scale and the moment magnitude scale are commonly used to quantify earthquake magnitude. Minor earthquakes, with magnitudes ranging from 2.0 to 3.9, are often imperceptible or barely noticeable. They might cause minimal damage to structures and infrastructure. However, moderate earthquakes, withmagnitudes between 4.0 and 6.0, can cause noticeable shaking and, depending on the proximity to populated areas, can result in moderate damage.Secondly, major earthquakes, with magnitudes between 6.0 and 7.9, are significant geological events that can cause widespread destruction, loss of life, and economic devastation. These earthquakes generate strong seismic waves that can be felt over large distances and result in severe shaking. Infrastructure, including buildings, bridges, and roads, is particularly vulnerable during major earthquakes, often leading to collapses and widespread damage. The aftermath of major earthquakes can include disrupted utilities such as water, electricity, and communication networks, exacerbating the challenges faced by affected communities.Furthermore, earthquakes with magnitudes exceeding 8.0 are classified as great earthquakes. These seismic events unleash immense energy, causing catastrophic destruction and loss of life. Great earthquakes are relatively rare but can have far-reaching consequences, including tsunamis,landslides, and secondary hazards such as fires and liquefaction. The 2004 Indian Ocean earthquake and tsunami, with a magnitude of 9.1–9.3, is one of the deadliest natural disasters in recorded history, resulting in over 230,000 fatalities across multiple countries.Apart from magnitude, earthquakes can also vary in depth, location, and focal mechanism, influencing their expression and impact. Shallow earthquakes, occurringwithin the Earth's crust, tend to produce more intense shaking near the epicenter compared to deep earthquakes, which originate at greater depths. Additionally, the location of earthquakes along tectonic plate boundaries, such as transform faults, subduction zones, and divergent boundaries, can influence their characteristics. For instance, subduction zone earthquakes, where one tectonic plate is forced beneath another, can produce powerful megathrust earthquakes capable of generating tsunamis.In conclusion, earthquakes exhibit a wide range of expressions and impacts, from minor tremors to catastrophic events. Understanding the diverse manifestations ofearthquakes, including their magnitude, depth, and location, is essential for assessing seismic hazards, mitigating risks, and enhancing resilience in vulnerable communities. Through continued research, monitoring, and preparedness efforts, we can strive to minimize the devastating effectsof earthquakes and build safer, more resilient societies.。
希腊克里特MW6.0地震后的应力方向变化与强余震发生
第４６卷㊀第２期２０２４年３月地㊀震㊀工㊀程㊀学㊀报C H I N A E A R T H Q U A K EE N G I N E E R I N GJ O U R N A LV o l ．４６㊀N o ．２M a r c h ,２０２４㊀㊀收稿日期:２０２２Ｇ０９Ｇ２９㊀㊀基金项目:国家自然科学基金(４２１７４０７４,４１６７４０５５)㊀㊀第一作者简介:李金磊(１９９９－),男,硕士研究生,主要从事地震学㊁勘探地球物理等方面的研究工作.E Ｇm a i l :j l l e e ０６２０＠１６３．c o m .㊀㊀通信作者:万永革(１９６７－),男,研究员,主要从事构造应力场㊁地震应力触发等方面的研究工作.E Ｇm a i l :w a n y g ２１７２１７＠v i p．s i n a ．c o m．c n .李金磊,万永革．希腊克里特M W ６．０地震后的应力方向变化与强余震发生[J ]．地震工程学报,２０２４,４６(２):４９１Ｇ５００．D O I :１０．２００００/j．１０００Ｇ０８４４．２０２２０９２９００１L I J i n l e i ,WA N Y o n g g e ．S t r e s sd i r e c t i o nc h a n g ea n ds t r o n g a f t e r s h o c ko c c u r r e n c ea f t e r t h e M S ６．０e a r t h q u a k e i nC r e t e ,G r e e c e [J ]．C h i n aE a r t h q u a k eE n g i n e e r i n g J o u r n a l ,２０２４,４６(２):４９１Ｇ５００．D O I :１０．２００００/j．１０００Ｇ０８４４．２０２２０９２９００１希腊克里特M W ６．０地震后的应力方向变化与强余震发生李金磊１,２,万永革１,３(１．防灾科技学院,河北三河０６５２０１;２．中国地质大学(北京)地球物理与信息技术学院,北京１０００８３;３．河北省地震动力学重点实验室,河北三河０６５２０１)摘要:地震的震源机制是地壳应力变化的指示器,而地壳应力变化与强震的发生直接相关.前人研究了地震震源机制变化在视应力较高的走滑型大震前的应力变化过程,而未见到震源机制变化对视应力较低的正断型大震发生的指示作用的研究.文章以２０２１年希腊克里特M W ６．０正断型地震序列为例,通过计算地震序列震源机制解与区域应力场方向之间最小空间旋转角的变化,揭示应力变化与强震发生的关系.为保证震源机制解的准确性,采用多家机构确定的震源机制得到中心震源机制作为该地震的震源机制,而后采用该地震序列精确的震源机制求解当地应力场,最后计算地震震源机制与主震震源机制及与所估计的地壳应力场方向的空间旋转角随时间的变化,探索强震发生与应力场变化的关系.结果表明:在主震发生的短期内,余震震源机制与该区域应力场方向的空间旋转角较大,与其后小震级的弱地震活动对应;随后余震震源机制与应力场方向的空间旋转角减小,对应后面发生的３次M W ＞５．０的强余震,在此之后的长时间内余震震源机制和应力场方向的空间旋转角再次增大,对应的余震震级及频度皆明显下降.文章以２０２１年希腊克里特M W ６．０地震序列为例,发现视应力较低的正断型地震前也存在应力方向集中现象,为探索地震应力前兆提供了范例.关键词:希腊克里特地震序列;震源机制中心解;构造应力场;最小空间旋转角中图分类号:P ３１９．５６㊀㊀㊀㊀㊀㊀文献标志码:A㊀㊀㊀文章编号:１０００Ｇ０８４４(２０２４)０２－０４９１－１０D O I :１０．２００００/j．１０００Ｇ０８４４．２０２２０９２９００１S t r e s s d i r e c t i o n c h a n g e a n d s t r o n g af t e r s h o c ko c c u r r e n c e a f t e r t h e M S ６．０e a r t h qu a k e i nC r e t e ,G r e e c e L I J i n l e i １,２,WA N Y o n g ge １,３(１．I n s t i t u t e o f Di s a s t e rP r e v e n t i o n ,S a n h e ０６５２０１,H e b e i ,C h i n a ;２．S c h o o l o f G e o p h y s i c s a n dI n f o r m a t i o nT e c h n o l o g y ,C h i n aU n i v e r s i t y o f G e o s c i e n c e s ,B e i j i n g １０００８３,C h i n a ;３．H e b e iK e y L a b o r a t o r y o f E a r t h q u a k eD yn a m i c s ,S a n h e ０６５２０１,H e b e i ,C h i n a )A b s t r a c t :T h e f o c a lm e c h a n i s m o f e a r t h qu a k e s i sa n i n d i c a t o ro f t h ev a r i a t i o no f c r u s t a l s t r e s s ,w h i c h i s d i r e c t l y r e l a t e d t o t h e o c c u r r e n c e o f s t r o n g e a r t h q u a k e s．T od a t e,n o p r e v i o u s s t u d y h a s i n v e s t i g a t e d t h e i n d i c a t i o no f f o c a lm e c h a n i s m c h a n g et ot h eo c c u r r e n c eo fn o r m a lＧf a u l te a r t hＧq u a k e sw i t h l o wa p p a r e n t s t r e s s．T h i s p a p e r t a k e s t h e２０２１M W６．０e a r t h q u a k e s e q u e n c e i nC r e t e, G r e e c e,a s a ne x a m p l e t od e t e r m i n e t h e r e l a t i o n s h i p b e t w e e ns t r e s s v a r i a t i o na n d t h eo c c u r r e n c e o f s t r o n g e a r t h q u a k e s b y c a l c u l a t i n g t h em i n i m u ms p a t i a l r o t a t i o na n g l eb e t w e e n t h e e a r t h q u a k e s e q u e n c e＇s f o c a lm e c h a n i s m s a n d t h ed i r e c t i o no f t h e r e g i o n a l s t r e s s f i e l d．T h e f o c a lm e c h a n i s m s d e t e r m i n e db y m u l t i p l ea g e n c i e sw e r eu s e dt oo b t a i nt h ec e n t r a l f o c a lm e c h a n i s m a st h ef o c a l m e c h a n i s mo f t h e e a r t h q u a k e,t h u s e n s u r i n g t h e a c c u r a c y o f t h e f o c a lm e c h a n i s m．T h e n,t h e l o c a l s t r e s s f i e l dw a s d e t e r m i n e db y t h e e a r t h q u a k es e q u e n c e＇sa c c u r a t e f o c a lm e c h a n i s m．F i n a l l y,t h e s p a t i a l r o t a t i o na n g l e o f t h e c r u s t a l s t r e s s f i e l dw a s c a l c u l a t e d,a n d t h e r e l a t i o n s h i p b e t w e e n t h e o c c u r r e n c e o f s t r o n g e a r t h q u a k e s a n d t h e v a r i a t i o no f t h e s t r e s s f i e l dw a s e x p l o r e d．R e s u l t s i n d iＧc a t e t h a t t h e s p a t i a l r o t a t i o na n g l eb e t w e e n t h e f o c a lm e c h a n i s mo f a f t e r s h o c k s a n d t h ed i r e c t i o n o f t h e r e g i o n a l s t r e s s f i e l d i s l a r g e i n t h e s h o r t t e r ma f t e r t h em a i n s h o c k,t h e r e b y c o r r e s p o n d i n g t o t h ew e a ks e i s m i c i t y o f s u b s e q u e n t e a r t h q u a k e sw i t h s m a l lm a g n i t u d e s．C o n s e q u e n t l y,t h e s p aＧt i a l r o t a t i o na n g l e d e c r e a s e s,c o r r e s p o n d i n g t o t h e o c c u r r e n c e o f t h r e e s t r o n g a f t e r s h o c k s(M W＞５．０)．A f t e r t h a t,t h e s p a t i a l r o t a t i o n a n g l e i n c r e a s e s a g a i n f o r a l o n g t i m e,a n d t h em a g n i t u d e a n d f r e q u e n c y o f t h e c o r r e s p o n d i n g a f t e r s h o c k s d e c r e a s e．U s i n g t h e s a m e２０２１M W６．０e a r t h q u a k e s eＧq u e n c e a s a ne x a m p l e,t h e r e s u l t s r e v e a l t h a t t h e s t r e s s d i r e c t i o n c o n c e n t r a t i o n a l s o e x i s t s b e f o r e t h en o r m a lＧf a u l t e a r t h q u a k e sw i t h l o wa p p a r e n t s t r e s s．T h e r e f o r e,t h i s s t u d y p r o v i d e s a n e x a m p l e f o r t h e e x p l o r a t i o no f e a r t h q u a k e s t r e s s p r e c u r s o r s．K e y w o r d s:C r e t e e a r t h q u a k es e q u e n c e i nG r e e c e;c e n t r a l f o c a lm e c h a n i s m;t e c t o n i c s t r e s s f i e l d;m i n i m u ms p a t i a l r o t a t i o na n g l e０㊀引言地震的发生与地壳应力状态有着直接的因果关系,而震源机制解直观地反映了地震破裂几何特征和运动学特征,是研究区域构造应力的基础[１Ｇ４].从２０世纪９０年代开始,地震学家们就尝试从地震序列㊁震源机制解之间寻找一定的联系,来促进人们对发震机理和地震预测等研究领域的了解[５Ｇ７,１０].在唐山地震序列应力释放过程研究中,李钦祖等[５]根据唐山地震序列震源机制数据对其应力释放调整机制进行了分析,但对于这一过程中强余震震源机制与应力场的分布关系并未进行详细说明.王俊国等[６]利用H a r v a r du n i v e r s i t y测定的千岛岛弧地区地震的矩心矩张量(C MT)解,分析该地区震源机制一致性特征,结果表明大震前一致性参数重复出现低值.在研究１９９２年美国兰德斯M W７．３地震事件和１９９９年美国赫克托矿M W７．１地震事件时,万永革[７]利用K a g a n[８]提出的双力偶地震震源机制空间旋转以及H a u k s s o n[９]对美国南加州地区小震震源机制的详细数据,通过对比分析获得了该区域震源机制和主震震源机制之间１０年内的平均空间旋转角,并发现２次大震前小震均倾向于接近主震震源机制.韩晓明等[１０]利用美国南加州地区１９８１ ２０１１年间的地震震源机制解资料,研究发现小震发震应力场P轴向区域构造应力场主压力的趋近现象.前述研究的强震前震源机制所揭示的地震孕育过程均对应视应力较高的走滑型地震,而对于视应力较低的正断型强震前是否有类似的现象,目前未见报道.２０２１年９月２７日６时１７分２１秒(当地时间)在希腊克里特发生M W６．０正断型地震.震中位于３５．２４ʎN,２５．２７ʎE,震源深度６k m.随后发生多次强余震,并且均可得到多个机构给出的震源机制解.这为得到该地震发生后震源机制变化和余震发生的关系创造了良好的契机.本文以该正断型地震序列为实例进行研究,首先,为降低各机构震源机制解对于分析结论不确定性的影响,采用万永革[１１]提出的震源机制中心解的方法,运用L e v e n b e r gＧM a rＧq u a r d t方案获得主震和余震震源机制中心解;然后根据得到的震源机制中心解,求得地震序列的局部应力场,以备求解余震震源机制解和局部应力场最２９４㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀地㊀震㊀工㊀程㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀２０２４年优滑动节面的最小空间旋转角;最后,采用震源机制最小空间旋转角计算方法,得出该区域各时间段内震源机制中心解与该地区应力场节面最小空间旋转角的变化,以及主震震源机制和余震震源机制的最小空间旋转角随时间的变化,以此来分析地震发生与应力场方向集中的关系.１㊀震源机制中心解的求解克里特岛位于希腊岛弧前缘,是欧亚板块与非洲板块相互作用的结果,构造变形㊁地震活动极其频繁[１２Ｇ１３].该区域地质构造环境复杂,含有许多微板块运动及区域性尺度结构.本次地震余震较多,有网站(如E M S C网站,h t t p s://w w w．e m s cＧc s e m．o r g/＃２)提供了这次地震的主震震源机制,以及１６组余震的震源机制.考虑到该地区地震完整性,以M W３．０为所采用的地震序列目录震级下限.文中所用的地震序列目录如表１所列,包括１个M W６．０以上的地震事件㊁３个M W５．０~６．０地震事件和１３个M W５．０以下的地震事件(图１).表１㊀希腊克里特M W６．０主震及余震地震序列目录T a b l e１㊀C a t a l o g u e o f t h e M W６．０e a r t h q u a k e s e q u e n c e i nC r e t e,G r e e c e发震时刻(U T C)震中位置/(ʎ)震级大小(M W)震源深度/k m２０２１Ｇ０９Ｇ２７T０６:１７:２２．２３５．１１N,２５．２２E６．０１０２０２１Ｇ０９Ｇ２７T０７:３０:４９．０３５．１３N,２５．２５E４．６１４２０２１Ｇ０９Ｇ２７T０８:２１:５８．９３５．１１N,２５．２９E４．５１０２０２１Ｇ０９Ｇ２７T１０:２３:１２．４３５．０５N,２５．２６E４．０１０２０２１Ｇ０９Ｇ２７T１１:０２:２５．９３５．０６N,２５．２２E４．８１０２０２１Ｇ０９Ｇ２７T２０:１０:０１．８３５．１５N,２５．１７E４．４１０２０２１Ｇ０９Ｇ２８T０４:４８:０９．１３５．１１N,２５．１９E５．３１０２０２１Ｇ０９Ｇ２８T１２:０９:５０．４３５．１９N,２５．２４E３．９５２０２１Ｇ０９Ｇ２８T１５:１３:１６．１３５．０５N,２５．２３E４．３１０２０２１Ｇ１０Ｇ２０T０２:４４:０５．１３５．０４N,２５．３４E４．３１０２０２１Ｇ１０Ｇ２１T０８:１２:５８．９３５．１９N,２５．２５E４．３１０２０２１Ｇ１０Ｇ２１T０９:３８:３８．９３５．０９N,２５．２５E４．６１０２０２１Ｇ１０Ｇ２２T１０:１１:３１．２３５．１０N,２５．２０E４．４１０２０２１Ｇ１０Ｇ２２T１７:１２:５０．５３５．１８N,２５．３２E４．０８２０２１Ｇ１２Ｇ２９T０５:０８:０９．９３４．８５N,２５．０９E５．７６８２０２１Ｇ１２Ｇ２９T１６:４７:０９．２３４．８７N,２５．１２E５．１６７２０２１Ｇ１２Ｇ２９T２３:０６:３９．９３４．９２N,２５．００E４．２１０１．１㊀震源机制中心解求解震源机制是地壳应力场研究的关键基础资料,但由于各个机构采用的计算方法及参考资料各不相同,导致同一次地震震源机制离散性较大.为了找到最可靠的震源机制解,采用万永革[１１]提出的震源机制中心解模型来分析地震震源机制.首先设定某震源机制为起始值,对该值域进行一阶泰勒扩展;然后采用L e v e n b e r gＧM a r q u a r d t迭代法求出,同时逐步调整初始值;最后,将与各备选震源机制最小空间旋转角平方和最小的解答作为此次地震的中心解.图１㊀２０２１希腊克里特地震序列震中分布图F i g．１㊀D i s t r i b u t i o no f t h e e p i c e n t e r s o f t h e２０２１C r e t ee a r t h q u a k e s e q u e n c e i nG r e e c e１．２㊀主震震源机制中心解的求解整理主震数据并列于表２.震源机制中心解(表２第３列)和相应的起始解标准差(表２第４列)是将每个机构确定的希腊克里特M W６．０地震震源机制解(表２第２列)作为起始解计算出来的.经过比较后得出:无论使用哪家机构得到的震源机制结果,差别都很小,对应标准差只发生在小数点之后５位处.结果表明,用这种方法所获得的震源机制的中心解是稳定可靠的.即便如此,我们依然选择标准差最小的震源机制解作为最终解.对于这次地震,我们发现用雅典国家天文台(N a t i o n a lO b s e r v aＧt o r y o fA t h e n s,N O A)测量的震源机制解为起始解所得到的标准偏离值最小,将此中心解(第一个节面走向㊁倾角和滑动角的值分别是:３２．０５ʎ,４０．９１ʎ,－９２．１２ʎ;另一个节面走向㊁倾角和滑动角的值分别是:２１４．８５ʎ,４９．１３ʎ,－８８．１６ʎ)当做最终结果(表２第８行).根据走向㊁倾角和滑动角与压应力轴㊁张应力轴㊁中间轴间的关系[１４],可以得到压应力轴走向和倾伏角分别为１４２．２８ʎ,８５．６６ʎ,不确定范围为４６．０８ʎ~２９６．０４ʎ和８２．８７ʎ~１０３．９７ʎ;张应力轴走向３９４第４６卷第２期㊀㊀㊀㊀㊀㊀㊀李金磊,等:希腊克里特M W６．０地震后的应力方向变化与强余震发生㊀㊀㊀㊀㊀㊀㊀和倾伏角分别为３０３．５５ʎ,４．１１ʎ,不确定范围为２８５．０２ʎ~３２２．０２ʎ和－１４．４１ʎ~２２．５７ʎ;中间轴走向和倾伏角分别为３３．６５ʎ,１．３９ʎ,不确定范围为１５．１２ʎ~５２．１２ʎ和－１０．５８ʎ~１３．４０ʎ.表２㊀２０２１年９月２７日６:１７希腊克里特M W６．０地震震源机制解T a b l e２㊀F o c a lm e c h a n i s ms o l u t i o n s o f t h e M W６．０e a r t h q u a k e i nC r e t e,G r e e c e a t６:１７o nS e p t e m b e r２７,２０２１序号震源机制解/(ʎ)走向倾角滑动角中心解/(ʎ)走向倾角滑动角作为起始解得到的标准差S/(ʎ)以N O A为起始解得到的最小空间旋转角/(ʎ)机构１２３０４１－６８２１４．８１４９．１１－８８．２２１９．２６５３４３１６．３７I N G V ２２１８５７－８５２１４．８３４９．０６－８８．２０１９．２６５３５６８．３６G F Z ３２３９２８－５５２１４．８６４９．０７－８８．１８１９．２６５３１３２９．０６C P P T ４２４３８－１１１３２．０７４０．９０－９２．１１１９．２６５３１１１３．９５I P G P ５２１２５－７５３２．００４０．８９－９２．１７１９．２６５３９０３１．３６U O A ６２０７５０－１０１２１４．８６４９．０７－８８．１７１９．２６５３１７９．８１K O E R I ７４５２０－９０３２．０７４０．９０－９２．１１１９．２６５３１１２３．６６O C A ８２６３１－８０３２．０５４０．９１－９２．１２１９．２６５３０８２０．００N O A ９４２４４－８４３２．０４４０．８９－９２．１４１９．２６５３２９７．４３G C MT １０２１５３５－１０６２１４．８５４９．０７－８８．１９１９．２６５３２５２２．８０U S G S １１３５４７－９７３２．０３４０．８９－９２．１５１９．２６５３５１９．５１E R D㊀㊀由于震源机制P㊁T㊁B轴的二义性,通过４种坐标轴旋转方式可以完全由一个震源机制的P㊁T㊁B 轴旋转到另外一个震源机制的P㊁T㊁B轴上.这４种旋转角度中最小的一个可以代表这两个震源机制的差别,通常称为最小空间旋转角[１１].表２第５列给出了不同机构发布的震源机制和作者测定的中心解之间的最小空间旋转角.经比较可知,此震源机制和中心解的最小空间旋转角的最小值为７．４３ʎ,最大值为３１．３６ʎ,最小三维空间旋转角的标准差最小值为１９．２７ʎ.必须指出,尽管由N O A提出的震源机制解作为起始解得到的实际中心解的标准差为最小值,但这并不代表此解离实际震源机制中心解之间的空间距离最近,而本次地震离实际中心解较近者应是G C MT(G l o b a lC e n t r o i d M o m e n tT e n s o r).这一现象的根源在于,求解中心解是一个具有非线性性质的问题,用雅克比矩阵求解各参数偏量时有可能超过或达不到最优解(表２第３列),这是本文利用各机构实测震源机制解反演初值的基础.将最终确定的中心震源机制解的不确定性以及空间三维辐射花样绘制于图２.图２(a)中黑色曲线为震源机制中心解两个不同节面,绿色曲线所含区域范围为其不确定区间;中心震源机制解压缩轴㊁拉张轴与中间轴则分别以红㊁蓝㊁黄点表示,四周相应颜色的圆圈是其不确定度区间,绿色㊁黑色和蓝色的小点代表每个作者获得的震源机制解的压缩轴㊁张力轴和中间轴的分布;紫色弧是每个作者获得的震源机制解节面.图２(b)中的压缩范围为蓝色,拉张范围为红色.１．３㊀余震震源机制中心解的求解㊁分类及总体特征分析１６组余震震源机制中心解汇总于表３,其各余震最后确定的中心震源机制解及其不确定性绘于图３中,空间三维辐射花样绘于图４.地震震源机图２㊀２０２１年９月２７日希腊克里特M W６．０地震震源机制解F i g．２㊀F o c a lm e c h a n i s ms o l u t i o no f t h e M W６．０e a r t h q u a k e i nC r e t e,G r e e c e,o nS e p t e m b e r２７,２０２１４９４㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀地㊀震㊀工㊀程㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀２０２４年表３㊀余震震源机制中心解T a b l e ３㊀C e n t r a l f o c a lm e c h a n i s ms o l u t i o no f t h e a f t e r s h o c k s序号发震时间震源机制解/(ʎ)走向倾角滑动角以该机构为起始解得到的最小空间旋转角/(ʎ)数据来源机构a ０９Ｇ２７T ０７:３０４４．３４４４．２７－１００．７７１８．３２O C A ㊁G F Z ㊁ U O A b ０９Ｇ２７T ０８:２１１９１．１３６０．２４－９５．５９１４．６９U O A ㊁ G F Zc ０９Ｇ２７T １０:２３７１．５４４７．２８－４９．５０１６．０５O C A ㊁ U O Ad ０９Ｇ２７T １１:０２４０．４０７９．３６－８９．９２３４．３３O C A ㊁ U O Ae０９Ｇ２７T ２０:１０７．０９３３．６８－１４９．５３３４．９６O C A ㊁ U O A f ０９Ｇ２８T ０４:４８２１．００５４．３５－１０２．６２１６．７９E R D ㊁G F Z ㊁K O E R I ㊁C P PT ㊁U O A ㊁I N G V ㊁O C A ㊁ N O Ag ０９Ｇ２８T １２:０９３３．４２７９．３１－８２．６４４１．４５O C A ㊁ U O A h ０９Ｇ２８T １５:１３１９３．１７３８．９８－９０．５４４．７４U O A ㊁ G F Z i １０Ｇ２０T ０２:４４０．２１５７．０３－１３５．７９５３．６１U O A ㊁ N O Aj １０Ｇ２１T ０８:１２２４０．６４４１．９４－７０．１０１１．８４G F Z ㊁N O A ㊁ U O A k１０Ｇ２１T ０９:３８２４７．９４４８．５１－６０．６３７．６２U O A ㊁ G F Zl １０Ｇ２２T １０:１１２５３．７４４５．８５－５１．０１１２．９２G F Z ㊁N O A ㊁O C A ㊁ U O Am １０Ｇ２２T １７:１２２７８．８４３２．２４－２１．９８２２．５３O C A ㊁ U O A n１２Ｇ２９T ０５:０８１６６．６０５２．０９６．１６１１．９６K O E R I ㊁N O A ㊁G F Z ㊁O C A ㊁I N G V ㊁ G C M To １２Ｇ２９T １６:４７１７３．６０５６．６８１８．１０１７．７０U O A ㊁I N G V ㊁G F Z ㊁N O A ㊁ K O E R Ip１２Ｇ２９T ２３:０６７．４６５８．５３－１２７．６７１２．１３U O A ㊁ N O A 注:标表示以该机构为初始解图３㊀１６组余震最终确定的中心震源机制解F i g ．３㊀T h e d e t e r m i n e d c e n t r a l f o c a lm e c h a n i s ms o l u t i o n s o f t h e １６a f t e r s h o c k s i n２０２１C r e t e e a r t h q u a k e s e qu e n c e ５９４第４６卷第２期㊀㊀㊀㊀㊀㊀㊀李金磊,等:希腊克里特M W ６．０地震后的应力方向变化与强余震发生㊀㊀㊀㊀㊀㊀㊀图４㊀１６组余震最终确定的空间三维辐射花样F i g．４㊀T h e f i n a l３ＧDr a d i a t i o n p a t t e r no f１６a f t e r s h o c k s制分类对于地震动力学分析有着重要作用.采用万永革[１１,１５]提出的震源机制水平应变花面应变的地震震源机制分类方法.图５表示了２０２１年希腊克里特地震序列的余震震源机制分类情况,其中正断型地震有１１个,占总体数量的６８．７５％;正走滑型地震有３个,占总体数量的１８．７５％;走滑型地震有１个,占总体数量的６．２５％;逆走滑型地震有１个,占总体数量的６．２５％.再考虑到主震为正断型地震,总体来讲该地震序列的震源机制以正断型和正走滑型为主,应属于正断型的构造应力背景.而研究区东北部的K a s t e l l i断层(图１)也是N N EＧS S W 为走向的正断层体系[１６],佐证了该地区为正断型应力体系.２㊀应力场方向和相对大小的求解地震的孕育和发生是地壳内应力㊁应变长期积累与释放的结果,通过运用数值模拟技术对现代应力场的产生和发展过程进行系统分析研究,也是探究地震产生机理的一种有效手段.为解决研究区域应力场的方向及其相对大小问题,本文采用万永革等[１４,１７Ｇ１９]基于断层面上应力张量剪应力方向符合断层面上滑动方向以及断层滑动的性质,所提出的擦痕数据结合定性断层滑动数据及相应位置在应力场按照搜索１ʎ的方向间隔和０．１的应力比值间隔网格搜索的方法,为反演参数提供一定置信度的置信区三角形的三个边分别为震源机制P,T和B轴倾伏角的刻度,三角形中的点划线表示震源机制类型分类的界限.相对面应变(A s)以图下方的色棒为标准采用背景颜色绘制.白线为网格线; S S:走滑型;N S:正走滑型;N:正断型;R S:逆走滑型;R:逆断型图５㊀２０２１年希腊克里特地震序列的余震震源机制分类及总体特征分析F i g．５㊀C l a s s i f i c a t i o na n do v e r a l l c h a r a c t e r i s t i c s a n a l y s i s o fa f t e r s h o c k f o c a lm e c h a n i s m s o f t h e２０２１C r e t ee a r t h q u a k e s e q u e n c e i nG r e e c e６９４㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀地㊀震㊀工㊀程㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀２０２４年间.利用先前求解得到的主震及余震序列的震源机制中心解(表２第８行第３列㊁表３第３列),采用网格搜索法对应力场进行求解.应力场反演如图６所示,从中可以看出在９５％置信度下,最优解的置信范围都较小,说明以图中结果来反映此区域应力场是较为准确的.最终求得该地区应力场最优节面参数:走向２９３ʎ,倾角６７ʎ,滑动角－５７ʎ.根据走向㊁倾角㊁滑动角与压缩轴㊁张力轴㊁中间轴间的关系[１９],(a)图中黑弧代表选定的 可能断层面 施密特投影,球外蓝色箭头即S１轴的水平方向,球内蓝色小箭头即 可能断层面＂观测错动方位.球体外侧面红色箭头为S３轴水平方向,内侧面红色小箭头为 可能断层面 理论错动方向.绿色曲线表示置信度９５％应力场中最大剪应力节面,黄色箭头表示该节面的错动方向,红色㊁黄色和蓝色封闭曲线分别表示主压应力轴㊁中应力轴和主张应力轴９５％置信度下的置信区间.(b)图为R＝０．９情况下的应力辐射花样图,红色代表压缩轴,蓝色代表拉伸轴图６㊀应力场反演成果F i g．６㊀I n v e r s i o n r e s u l t s o f s t r e s s f i e l d得到压缩轴走向和倾伏角分别为２４５．９８ʎ,５５．４５ʎ,不确定范围分别为２４２．９５ʎ~２４６．９８ʎ和５４．４７ʎ~５５．９５ʎ;张力轴走向和倾伏角分别为３５９．７７ʎ,１５．５２ʎ,不确定范围分别为３５８．７７ʎ~３６０．７７ʎ和１５．０２ʎ~１６．０２ʎ;中间轴走向和倾伏角分别为９９．００ʎ,３０．００ʎ,不确定范围分别为９８．００ʎ~１００．００ʎ和２９．５０ʎ~３０．５０ʎ.其中,应力形因子R＝(S２－S３)/ (S１－S３),这里S１㊁S２和S３是在主轴坐标系下的三个本征值,分别代表主张应力㊁中间应力和主压应力的相对大小,拉张为正.３㊀最小空间旋转角计算结果与分析通过比较各震源机制中心解与该地区应力场节面的最小空间旋转角,可以定量得出震源机制中心解间的差别 其值越小表明此地震与该地区应力场节面的差别越小,反之亦然.按照每一个地震的发震时间,将各余震震源机制中心解(表３第３列)㊁主震震源机制中心解(表２第３列)与应力场最优节面解(走向２９３ʎ,倾角６７ʎ,滑动角－５７ʎ)之间的最小空间旋转角整合成表４.图７(a)显示了每个余震震源机制中心解与主震震源机制中心解之间最小空间旋转角的关系变化.表４㊀各震源机制中心解与主震震源机制中心解及该地区应力场节面的最小空间旋转角T a b l e４㊀M i n i m u ms p a t i a l r o t a t i o na n g l e s b e t w e e n t h e c e n t r a lf o c a lm e c h a n i s mo f a f t e r s h o c k s w i t h t h e c e n t r a l f o c a lm e c h a n i s mo fm a i n s h o c ka n d t h e s t r e s s f i e l d i nt h i sr e g i o n序号发震时间各震源机制中心解与主震震源机制中心解的最小空间旋转角/(ʎ)各震源机制中心解与该地区应力场节面的最小空间旋转角/(ʎ) a０９Ｇ２７T０７:３０１９．８４４９．３１b０９Ｇ２７T０８:２１２３．１３９０．１１c０９Ｇ２７T１０:２３３０．９８８０．８８d０９Ｇ２７T１１:０２３９．１３７１．５０e０９Ｇ２７T２０:１０４０．８１４１．９１f０９Ｇ２８T０４:４８１５．９７６８．１５g０９Ｇ２８T１２:０９３９．３７８１．４６h０９Ｇ２８T１５:１３２２．４３８６．２５i１０Ｇ２０T０２:４４３６．０９６０．９２j１０Ｇ２１T０８:１２１９．６４５１．９８k１０Ｇ２１T０９:３８２５．３３４７．０６l１０Ｇ２２T１０:１１３０．３５４７．８６m１０Ｇ２２T１７:１２４５．５０５７．０８n１２Ｇ２９T０５:０８８５．９４８９．６６o１２Ｇ２９T１６:４７９１．６６９０．６４p１２Ｇ２９T２３:０６３１．９１６０．２５７９４第４６卷第２期㊀㊀㊀㊀㊀㊀㊀李金磊,等:希腊克里特M W６．０地震后的应力方向变化与强余震发生㊀㊀㊀㊀㊀㊀㊀图７㊀最小空间旋转角与地震活动关系F i g．７㊀R e l a t i o n s h i p b e t w e e n t h em i n i m u ms p a t i a l r o t a t i o na n g l e a n d s e i s m i c a c t i v i t y图７(b)为各震源机制中心解与该地区应力场节面的最小空间旋转角关系变化.图７(c)为希腊克里特岛M W６．０主震和余震地震序列的MＧT图.通过对数据的比较,将所有余震活动分成三个阶段:在主震发生后的４８h内,各个余震震源机制的中心解与该区域应力场节面的最小空间旋转角明显较大,且明显靠近主震震源机制中心解,在达到１次震级为M W５．３(表１第８行)的强余震后,余震数量及震级明显降低,其震源机制中心解与该区域应力场节面的最小空间旋转角出现减小的趋势;主震发生一个月后,余震又呈集群式出现,此时余震的数量及出现的最大震级均小于第一阶段,且各个余震震源机制的中心解与该区域应力场节面的最小空间旋转角明显减小;主震发生三个月后,余震再次集群出现,但此次仅在数量上少于前两次,震级整体较前两次高,出现２次M W５．０(表１第１６㊁１７行)以上的强余震,最高达M W５．７,其震源机制最小空间旋转角与该区域应力场节面的最小空间旋转角明显增大;直到２０２２年９月该地区未再发生震级达M W５．０以上的强余震.而这三个阶段可以按照强震前的地震发生与地壳应力场的一致性相关来解释.主震后４８h内发生的地震震源机制与地壳应力场相差较大(最小空间旋转角较大),预示着震源机制发生的应力场较为混乱,没有主流的方向,说明地壳应力得到了较大释放,使应力场的方向的主流方向不明显,意味着后面强震发生的可能性较小,而主震一个月后的余震丛中的确没有大的地震发生.这些地震震源机制与应力场的差别(最小空间旋转角)明显变小,意味着震源机制的发生与应力场较为一致,呈现了地震发生的震源机制的主流方向,预示着将来会有较强地震发生,结果在主震发生后的１２月２９日,发生了本次余震序列的最大地震.在本次地震丛中,震源机制与应力场的最小空间旋转角再次增大,意味着后面没有强余震发生.到目前为止,还未见到较大地震的发生,这说明余震的震源机制与局部应力场的最小空间旋转角确实跟强震的发生具有时空对应关系.仿照前人采用地震和主震震源机制的最小三维空间旋转角来解释强震发生的研究[７,１０],本研究也计算了本次地震序列的余震和主震震源机制的最小空间旋转角随时间的变化[图７(a)].我们发现,主震后４８h内的余震震源机制与主震震源机制的三维空间旋转角较小,且后面的两丛余震表现与应力场最优节面㊁余震震源机制的最小三维空间旋转角８９４㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀地㊀震㊀工㊀程㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀２０２４年是变化一致的,这一方面说明前人采用震源机制和主震震源机制的最小空间旋转角代表应力场是可行的;另一方面也表明,主震震源机制的表现不一定代表应力场的应力变化情况,而采用局部应力场进行最小空间旋转角才是最合适的.４㊀结论与讨论本文从E M S C网站收集到２０２１年希腊克里特岛地区M W６．０地震后多家机构提供的多次余震资料,采用万永革[１１]提出的震源机制中心解程序求解了主震和余震序列的震源机制中心解,按照搜索１ʎ的方向间隔和０．１的应力比值间隔,通过网格搜索法对应力场展开求解,计算了各震源机制中心解与该地区应力场节面的最小空间旋转角.通过对比研究结果,证实了地震震源机制与局部应力场最优节面震源机制的最小空间旋转角与强震的发生有明显的对应关系,最小空间旋转角的增大意味着其后的地震危险性降低,而最小空间旋转角的减小意味着后续该地区的地震危险性增高.需要指出的是,这里的最小空间旋转角究竟多低才是后续强震发生的阈值,后续的强震的震级可能是多大,这些问题目前还没有一致的标准.本文只是从短时间较为密集的地震震源机制数据的角度给出了一个实例.针对这些问题进行进一步研究也许是将来的一个方向,对地震预测研究有一定帮助.地震释放能量和地震矩关系的研究表明:走滑型地震多具有较高的视应力水平,为倾滑型地震的数倍[２０Ｇ２２].对全球强震之间的触发研究认为具有较低视应力水平的逆冲地震更容易被触发.前人研究的很多地球物理现象与震源机制类型有关,如潮汐对地震的触发[２３]㊁前震发生率[２４]㊁震级频度关系[２５].前人讨论了视应力较高的走滑型强震发生前呈现明显的应力轴与主震震源机制的趋近[７],对于倾滑型强震是否也可以观测到应力方向集中现象,目前尚不清楚.本文仅对正断型地震给出了强震前震源机制与局部应力场方向一致的实例,而中国大陆有很多正断型的地堑带,如藏南亚东 谷露裂谷带㊁山西地堑带等,这些地区发生正断型的地震的可能性较大.本研究可为正断型地震之前的应力方向集中提供参考.将来也许从震源机制类型分类讨论强震之前的震源机制的变化趋势是地震预测研究的一个方向.参考文献(R e f e r e n c e s)[１]㊀万永革,沈正康,盛书中,等．２００８年汶川大地震对周围断层的影响[J]．地震学报,２００９,３１(２):１２８Ｇ１３９．WA N Y o n g g e,S H E N Z h e n g k a n g,S H E N G S h u z h o n g,e ta l．T h e i n f l u e n c eo f２００８W e n c h u a ne a r t h q u a k eo ns u r r o u n d i n gf a u l t 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o g y[M]．B e i j i n g:S c i e n c eP r e s s,２０１６:３９５Ｇ４０２．[１５]㊀万永革．震源机制水平应变花面应变的地震震源机制分类方法及序列震源机制总体特征分析[J/O L]．地球科学,２０２２:１Ｇ１６(２０２２Ｇ０９Ｇ２９)[２０２３Ｇ０４Ｇ０２]．h t t p://k n s．c n k i．n e t/k c m s/d eＧt a i l/４２．１８７４．p．２０２２０７１５．１５３２．０１４．h t m l．WA N Y o n g g e．F o c a lm e c h a n i s m c l a s s i f i c a t i o nb a s e do na r e a ls t r a i no f t h eh o r i z o n t a l s t r a i nr o s e t t e o f f o c a lm e c h a n i s ma n dc h a r a c t e r i s t i c a n a l y s i s o f o v e r a l l f o c a lm e c h a n i s mo f t h e e a r t hＧq u a k e s e q u e n c e[J/O L]．E a r t hS c i e n c e,２０２２:１Ｇ１６(２０２２Ｇ０９Ｇ２９)[２０２３Ｇ０４Ｇ０２]．h t t p://k n s．c n k i．n e t/k c m s/d e t a i l/４２．１８７４．p．２０２２０７１５．１５３２．０１４．h t m l．[１６]㊀C A P U T O R,C A T A L A N OS,MO N A C O C,e t a l．M i d d l eＧl a t e Q u a t e r n a r yg e o d y n a m i c s o fC r e t e,s o u t h e r nA e g e a n,a n d s e i sＧm o t e c t o n i c i m p l i c a t i o n s[J]．B u l l e t i no f t h eG e o l o g i c a l S o c i e t yo fG r e e c e,２０１７,４３(１):４００．[１７]㊀W A N YG,S H E N GSZ,H U A N GJC,e t a l．T h e g r i d s e a r c ha lＧg o r i t h mo f t e c t o n i c s t r e s s t e n s o rb a s e do nf o c a lm e c h a n i s m d a t aa n d i t sa p p l i c a t i o ni nt h eb o u n d a r y z o n eo fC h i n a,V i e t n a m a n dL a o s[J]．J o u r n a l o f E a r t hS c i e n c e,２０１６,２７(５):７７７Ｇ７８５．[１８]㊀万永革．联合采用定性和定量断层资料的应力张量反演方法及在乌鲁木齐地区的应用[J]．地球物理学报,２０１５,５８(９):３１４４Ｇ３１５６．WA N Y o n g g e．A g r i d s e a r c hm e t h o d f o r d e t e r m i n a t i o no f t e cＧt o n i c s t r e s st e n s o ru s i n gq u a l i t a t i v ea n d q u a n t i t a t i v ed a t ao fa c t i v e f a u l t sa n d i t sa p p l i c a t i o nt ot h eU r u m q i a r e a[J]．C h iＧn e s e J o u r n a l o fG e o p h y s i c s,２０１５,５８(９):３１４４Ｇ３１５６．[１９]㊀万永革,盛书中,许雅儒,等．不同应力状态和摩擦系数对综合P波辐射花样影响的模拟研究[J]．地球物理学报,２０１１,５４(４):９９４Ｇ１００１．WA N Y o n g g e,S H E N G S h u z h o n g,X U Y a r u,e ta l．E f f e c to fs t r e s s r a t i o a n d f r i c t i o n c o e f f i c i e n t o n c o m p o s i t e Pw a v e r a d i aＧt i o n p a t t e r n s[J]．C h i n e s e J o u r n a l o fG e o p h y s i c s,２０１１,５４(４):９９４Ｇ１００１．[２０]㊀C HO Y GL,B O A TWR I G H TJL．G l o b a l p a t t e r n so f r a d i a t e d s e i s m i c e n e r g y a n da p p a r e n t s t r e s s[J]．J o u r n a l o fG e o p h y s i c a lR e s e a r c h:S o l i dE a r t h,１９９５,１００(B９):１８２０５Ｇ１８２２８．[２１]㊀PÉR E ZＧC AM P O SX,B E R O Z A G C．A na p p a r e n tm e c h a n i s md e p e n d e n c e o f r a d i a t e d s e i s m i c e n e r g y[J]．J o u r n a l o f G e o p h y sＧi c a lR e s e a r c h(S o l i dE a r t h),２００１,１０６(B６):１１１２７Ｇ１１１３６．[２２]㊀WUZL．S c a l i n g o f a p p a r e n t s t r e s s f r o m b r o a d b a n dr a d i a t e de n e r g y c a t a l o g u e a n ds e i s m i cm o m e n t c a t a l o g u ea n d i t sf o c a lm e c h a n i s md e p e n d e n c e[J]．E a r t h,P l a n e t s a n dS p a c e,２００１,５３(１０):９４３Ｇ９４８．[２３]㊀T S U R U O K A H,O H T A K E M,S A T O H．S t a t i s t i c a l t e s to f t h e t i d a l t r i g g e r i n g o f e a r t h q u a k e s:c o n t r i b u t i o no f t h eo c e a nt i d el o a d i n g e f f e c t[J]．G e o p h y s i c a lJ o u r n a lI n t e r n a t i o n a l,１９９５,１２２(１):１８３Ｇ１９４．[２４]㊀R E A S E N B E R GPA．F o r e s h o c ko c c u r r e n c e r a t e sb e f o r e l a r g ee a r t h q u a k e sw o r l d w i d e[J]．P u r e a n d A p p l i e d G e o p h y s i c s,１９９９,１５５(２):３５５Ｇ３７９．[２５]㊀F R O H L I C H C,D A V I SS D．T e l e s e i s m i c b v a l u e s;o r,m u c ha d oab o u t１．０[J]．J o u r n a lo f G e o p h y s ic a lR e s e a r c h(S o l i dE a r t h),１９９３,９８(B１):６３１Ｇ６４４．(本文编辑:贾源源)００５㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀地㊀震㊀工㊀程㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀２０２４年。
地理信息系统导论课后题参考答案
Chapter 1 Review Questions1. Define geospatial data.Geospatial data are data that describe both the locations and characteristics of spatial features such as roads, land parcels, and vegetation stands on the Earth’s surface.2. Describe an example of GIS application from your discipline.[Refer to Section 1.2 and describe an example of GIS application from geography, forestry, geology, environmental studies, business, public health, etc.]3. Go to the USGS National Map website (/viewer.html) and see what kinds of geospatial data are available for download.[Go to the above website, follow the instructions at the website, and check for geospatial data available for download.]4. Go to the National Institute of Justice website(/nij/maps/) and read how GIS is used for crime analysis.[Go to the above website. “Learn about Crime Mapping” is included in the lower right corner. It lists three topics: What is GIS; Mapping Crime: Principle and Practice; and Understanding Hot Spots.]5. Location-based services are probably the most commercialized GIS-related field. Search for “location-based service” in Wikipedia(/) and read what has been posted on the topic. Accessed on August 9, 2010, Wikipedia defines a location-based service as “an information and entertainment service, accessible with mobile devices through the mobile network and utilizing the ability to make use of the geographical position of the mobile device.”6. What types of software and hardware are you currently using for GIS classes and projects?[Name the software package (e.g., ArcGIS 10.2) and the hardware (e.g., PC Windows 7) for the GIS class.]7. Try the map locators offered by Microsoft Virtual Earth, Yahoo Maps, and Google Maps, respectively. State the major differences among these three systems.[Go to each website, try the map locator, and summarize, in your opinion, the major differences between the map locators.]8. Define geometries and attributes as the two components of GIS data. Geometries describe the locations of spatial features, which may be discrete or continuous. Attributes describe the characteristics of spatial features.9. Explain the difference between vector data and raster data.Vector data use points and their x-, y-coordinates to represent spatial features of points, lines, and areas. Raster data use a grid and grid cells to represent the spatial variation of a feature.10. Explain the difference between the georelational data model and theobject-based data model.The georelational data model uses a split system to store geometries and attributes. The object-based data model stores geometries and attributes in a single system.11. What does it mean by "volunteered geographic information"? Volunteered geographic information is geographic information generated by the public using web applications and services.12. Suppose you are required to do a GIS project for a class. What kinds of activities or operations do you have to perform to complete the project?[The project will most likely involve data input, data management, data display, data exploration, data analysis, and, in some cases, GIS models and modeling.]13. Name two examples for vector data analysis.Examples for vector data analysis include buffering, overlay, distance measurement, spatial statistics, and map manipulation.14. Name two examples of raster data analysis.Examples of raster data analysis includes local, neighborhood, zonal, and global operations.15. Describe an example from your discipline, in which a GIS can provide useful tools for building a model.[A GIS can be used for building simple models. For more complex models such as environmental models, a GIS is typically used for data visualization, database management, and data exploration.]Chapter 2 Review Questions1. Describe the three levels of approximation of the shape and size of the Earth for GIS applications.The simplest model for approximating the Earth is a sphere, which is typically used in discussing map projections. But the Earth is wider along the equator than between the poles. Therefore a better approximation to the shape of the Earth is a spheroid, also called ellipsoid, an ellipse rotated about its minor axis. The geoid is an even closer approximation of the Earth than a spheroid. The geoid has an irregular surface, which is affected by irregularities in the density of the Earth’s crust and mantle.2. Why is the datum important in GIS?A datum is important in GIS because it serves as the reference or base for calculating the geographic coordinates of a location.3. Describe two common datums used in the United States.The first common datum used in the United States is NAD27(North American Datum of 1927), which is a local datum based on the Clarke 1866 ellipsoid, aground-measured spheroid. The second common datum is NAD83(North American Datum of 1983), an Earth-centered or geocentered datum, based on the GRS80 (Geodetic Reference System 1980) ellipsoid.4. Pick up a USGS quadrangle map of your area. Examine the information on the map margin. If the datum is changed from NAD27 to NAD83, what is the expected horizontal shift?[The expected horizontal shift is listed on the lower margin of a USGS quadrangle map.]5. Go to the NGS-CORS website (/CORS/). How many continuously operating reference stations do you have in your state? Use the links at the website to learn more about CORS.[Go to the above website, click a state on the map, and see how many continuously operating reference stations are within the state.] Surveyors, GIS professionals, engineers, scientists, and others can apply CORS data to position points at which GPS data have been collected. The CORS system enables positioning accuracies that approach a few centimeters relative to the National Spatial Reference System, both horizontally and vertically.6. Explain the importance of map projection.A map projection offers a couple of advantages. First, a map projection allows us to use two-dimensional maps, either paper or digital, instead of a globe. Second, a map projection allows us to work with plane or projected coordinates rather than longitude and latitude values. Computations with geographic coordinates are more complex.7. Describe the four types of map projections by the preserved property.A conformal projection preserves local angles and shapes. An equivalent projection represents areas in correct relative size. An equidistant projection maintains consistency of scale along certain lines. And an azimuthal projection retains certain accurate directions.8. Describe the three types of map projections by the projection or developable surface.A cylindrical projection uses a cylinder as the projection or developable surface, a conic projection uses a cone, and an azimuthal projection uses a plane.9. Explain the difference between the standard line and the central line.A standard line refers to the line of tangency between the projection surface and the reference globe. In other words, there is no projection distortion along a standard line. The central lines (i.e., the central parallel and meridian) define the center of a map projection.10. How is the scale factor related to the principal scale?The scale factor is defined as the ratio of the local scale to the principal scale. In other words, the scale factor is the normalized local scale.11. Name two commonly used projected coordinate systems that are based on the transverse Mercator projection.They are the Universal Transverse Mercator (UTM) grid system and the State Plane Coordinate (SPC) system.12. Google the GIS data clearinghouse for your state. Go to the clearinghouse website. Does the website use a common coordinate system for the statewide data sets? If so, what is the coordinate system? What are the parameters values for the coordinate system? And, is the coordinate system based on NAD27 orNAD83?[The coordinate system information is typically included on the clearinghouse page for data download.]13. Explain how a UTM zone is defined in terms of its central meridian, standard meridian, and scale factor.A UTM zone is mapped onto a secant case transverse Mercator projection, with a scale factor of 0.9996 at the central meridian. The standard meridians are 180 kilometers to the east and west of the central meridian.14. Which UTM zone are you in? Where is the central meridian of the UTM zone?[The answer can be found on the margin of a 1:24,000-scale USGS topographic map. It may also be available in the download information of the clearinghouse for your area. Figure 2.12 in the text can also provide the answer, but it is not as clear as on a USGS topographic map.]15. How many SPC zones does your state have? What map projections are the SPC zones based on?[Information on the SPC zones is available on the USGS topographic maps. It may also be available in the download information of the clearinghouse for your area.]16. Describe how on-the-fly projection works.A GIS package, if it offers on-the-fly projection, can use the projection files available with the data sets and automatically convert the data sets to a common coordinate system. This common coordinate system is by default the coordinate system of the first data set in display.Chapter 3 Review Questions1. Google the GIS data clearinghouse for your state. Go to the clearinghouse website. What data format(s) does the website use for delivering vector data? [The data formats may include the shapefile and the geodatabase from Esri.]2. Name the three types of simple features used in GIS and their geometric properties.A point has 0 dimension and has only the property of location. A line isone-dimensional and has the property of length. And a polygon is two-dimensional and has the properties of area (size) and perimeter.3. Draw a stream network, and show how the topological relationships of connectivity and contiguity can be applied to the coverage.[Draw a simple stream network, insert a node at each stream junction for connectivity, and mark the flow direction of each stream segment for contiguity.]4. How many arcs connect at node 12 in Figure 3.8?Three arcs (1, 2, and 3) connect at node 12.5. Suppose an arc (arc 8) is added to Figure 3.9 from node 13 to node 11. Write the polygon/arc list for the new polygons and the left/right list for arc 8. Polygon 101 in Figure 3.9 will be replaced by two new polygons. Suppose the new polygons are numbered 105 and 106, with 105 on the left of arc 8 and 106 on the right. Polygon 105 consists of arcs 1 and 8, and polygon 106 consists of arcs 8, 4, and6.6. Explain the importance of topology in GIS.Topology is important in GIS for three reasons. First, it ensures data quality, such as lines meeting perfectly and polygons closed properly. Second, topology can enhance certain types of GIS analysis such as geocoding and traffic volume analysis. Third, topological relationships between spatial features allow GIS users to perform spatial data query.7. What are the main advantages of using shapefiles?Shapefiles have two main advantages over topology-based data such as coverages. First, shapefiles can display more rapidly on the computer monitor. Second, shapefiles are nonproprietary and interoperable, meaning that they can be used across different software packages.8. Explain the difference between the georelational data model and theobject-based data model.The object-based data model differs from the georelational data model in two aspects. First, the object-based data model stores both the spatial and attribute data of spatial features in a single system rather than a split system. Second, the object-based data model allows a spatial feature (object) to be associated with a set of properties and methods.9. Describe the difference between the geodatabase and the coverage in terms of the geometric representation of spatial features.The geodatabase is similar to the coverage model in terms of the geometric representation of simple features. The difference between the two models lies mainly in the composite features of regions and routes. The geodatabase does not support the region subclass and replaces the route subclass with polylines with m (measure) values.10. Explain the relationship between the geodatabase, feature dataset, and feature class.Geodatabase, feature dataset, and feature class form a hierarchical structure. A geodatabase can contain one or more feature datasets, and a feature dataset can store one or more feature classes that share the same coordinate system and area extent.11. Feature dataset is useful for data management. Can you think of an example in which you want to organize data by feature dataset?[For example, census data sets such as counties, census tracts, and block groups can be stored as feature classes in a feature dataset called census.]12. Explain the difference between a personal geodatabase and a file geodatabase.A personal geodatabase stores data as tables in a Microsoft Access database with the mdb extension. A file geodatabase, on the other hand, stores data in many small-sized files in a folder with the gdb extension. The file geodatabase has no overall database size limit (as opposed to a two-gigabyte limit for the personal geodatabase) and can work across platforms (e.g., Windows as well as Linux).13. What is ArcObjects?ArcObjects is a collection of objects, properties, and methods, which provides the foundation for ArcGIS Desktop.14. Provide an example of an object from your discipline and suggest the kinds of properties and methods that the object can have.[For polygon features such as timber stands and census tracts, they can all have the properties of extent (i.e., xmin, ymin, xmax, and ymax) and spatial reference (i.e., coordinate system). These polygon or area projects can also have the method for deriving the centroid (i.e., the physical center of a polygon).]15. What is an interface?An interface represents a set of externally visible operations of an object. To use the properties and methods of an object, we work through an interface that has been implemented on the object.16. Table 3.1 shows “must not overlap” as a topology rule for polygon features. Provide an example from your discipline that can benefit from enforcing this topology rule.[Esri maintains a data model website, where one can download discipline-specific data models (/datamodels). For example, one can download the Census Administrative Boundaries Data Model poster by clicking Case Studies for Census-Administrative Boundaries on the page. The poster includes many topology rules between many census-related feature classes.]17. “Must not intersect” is a topology rule for line features. Provide an example from your discipline that can benefit from enforcing this topology rule.[Esri maintains a data model website, where one can download discipline-specific data models (/datamodels). For example, one can download the Census Administrative Boundaries Data Model poster by clicking Case Studies for Census-Administrative Boundaries on the page. The poster includes many topology rules between many census-related feature classes.]18. The text covers several advantages of adopting the geodatabase. Can you think of an example in which you would prefer the geodatabase to the coverage for a GIS project?[The geodatabase data model provides a convenient framework for storing and managing GIS data under different themes such as census, transportation, and so on. Each of the themes is treated as a feature dataset in the geodatabase.]19. Compare Figure 3.19 with Figure 3.21, and explain the difference between the geodatabase and the coverage in handling the route data structure.A route subclass in a coverage is built on arcs and sections, and its linear measures are based on the lengths of arcs. A route in a geodatabase has its linear measures stored as the m values, along with x- and y-coordinates in the geometry field.20. Draw a small TIN to illustrate that it is a composite of simple features. [Draw a couple of nonoverlapping triangles, and mark nodes, lines, and areas on the drawing.]Chapter 4 Review Questions1. What are the basic elements of the raster data model?The basic elements of the raster data model are cell value, cell size, cell depth, raster bands, and spatial reference.2. Explain the advantages and disadvantages of the raster data model vs. the vector data model.The main advantage of the raster data model is having fixed cell locations, which make it easier for data manipulation, aggregation, and analysis. The main disadvantage is its weakness in representing the precise location of spatial features. Also, raster data such as satellite images have large memory sizes.3. Name two examples each for integer rasters and floating-point rasters. Examples of integer rasters are land use and soil types. Examples of floating-point rasters are precipitation and elevation.4. Explain the relationship between cell size, raster data resolution, and raster representation of spatial features.A larger cell size means a lower raster data resolution and greater difficulty in representing spatial features with cells.5. You are given the following information on a 30-meter DEM:• UTM coordinates in meters at the lower-left corner: 560635, 4816399• UTM coordinates in meters at the upper-right corner: 570595, 4830380How many rows does the DEM have? How many columns does the DEM have? And, what are the UTM coordinates at the center of the (row 1, column 1) cell? The DEM has 466 rows and 332 columns. The center of the (row 1, column 1) cell has the UTM coordinates of 560650, 4816414.6. Explain the difference between passive and active satellite systems.A passive system acquires spectral bands from the electromagnetic spectrum reflected or emitted from the Earth’s surface, whereas an active system provides its own energy to illuminate an area of interest and measure the radar waves reflected or scattered back from the Earth’s surface.7. Go to either the GeoEye website (/) or the DigitalGlobe website (/), and take a look at their very high resolution sample imagery.[Click on Gallery on the Space Imaging web page to view sample images. Click on Sample Imagery on the DigitalGlobe web page to view sample images.]8. What is a digital elevation model?A digital elevation model consists of an array of uniformly spaced elevation data.9. Describe three new data sources for producing DEMs.DEMs can be produced using (1) stereo optical satellite images, (4) stereo SAR images, (5) LiDAR data10. Go to the USGS National Elevation Dataset website(/about.html) and check the kinds of DEM data that are available from the USGS.Four kinds of DEM data are listed at the website: 1/9 arc-second (approximately 3 meters) resolution, 1/3 arc-second (approximately 10 meters) resolution, 1 arc-second (approximately 30 meters) resolution, and 2 arc-second (approximately 60 meters) resolution.11. Google the GIS data clearinghouse for your state. Go to the clearinghouse website. Does the website offer USGS DEMs, DRGs, and DOQs online? Does the website offer both 30-meter and 10-meter USGS DEMs?[Typically the information about USGS DEMs, DRGs, and DOQs is included on the page for data download.]12. Use a diagram to explain how the run length encoding method works.13. Refer to the figure below, draw a quad tree, and code the spatial index of the shaded (spatial) feature.14. Explain the difference between lossless and lossy compression methods.A lossless compression method allows the original image to be precisely reconstructed. A lossy compression method cannot reconstruct fully the original image but can achieve high-compression ratios.15. What is vectorization?Vectorization refers to the conversion of raster data into vector data.16. Use an example from your discipline and explain the usefulness of integrating vector and raster data.[A common example is use of digital orthophoto for display with vector data such as roads or for editing vector data such as digitizing new roads.]Chapter 5 Review Questions1. What is a geoportal?A geoportal offers multiple services, including links to data services, news, references, a community forum, and often an interactive data viewer.2. List the spatial resolutions of DEMs available from the National Elevation Dataset.They are 30 meters for 1 arc second, 10 meters for 1/3 arc second, and 3 meters for1/9 arc second.3. What kinds of data are contained in the USGS DLG files?The USGS DLGs include hypsography (i.e., contour lines and spot elevations), hydrography, boundaries, transportation, and the U.S. Public Land Survey System.4. What is SSURGO?SSURGO stands for Soil Survey Geographic database, a database compiled from field mapping at scales ranging from 1:12,000 to 1:63,360 by the Natural Resources Conservation Service for uses at the farm, township, and county levels.5. Suppose you want to make a map showing the rate of population change between 2000 and 2010 by county in your state. Describe (1) the kinds of digital data you will need for the mapping project, and (2) the website(s) you will use to download the data.[(1) One will need the population data for 1990 and 2000 and a digital county map. (2) One can get the population data for 1990 and 2000 from the U.S. Census Bureau website and the digital county map from a state clearinghouse.]6. Google the GIS data clearinghouse for your state. Go to the clearinghouse website. Select the metadata of a data set and go over the information in each category.[The metadata of a data set is usually included on the data download page.]7. Define "neutral format" for data conversion.A neutral format is a public or de facto format for data exchange. Data in a neutral format can be imported to different GIS packages.8. What kinds of data are contained in the TIGER/Line files?TIGER/Line files contain legal and statistical area boundaries such as counties, census tracts, and block groups as well as roads, railroads, streams, water bodies, power lines, and pipelines.9. Describe two common types of field data that can be used in a GIS project. Two important types of field data that can be used in a GIS project are survey data and global positioning system (GPS) data.10. Explain how differential correction works.Differential correction uses correction factors available from a reference (base) station to reduce noise errors of data collected by a GPS receiver. Reference stations such as those participating in the National Geodetic Survey Continuously Operating Reference System are located at points that have been accurately surveyed.11. What types of GPS data errors can be corrected by differential correction? Differential correction can correct noise errors, which include ephemeris (positional) error, clock errors (orbital errors between monitoring times), atmospheric delay errors, and multipath errors (signals bouncing off obstructions before reaching the receiver).12. What kinds of data must exist in a text file so that the text file can be converted to a shapefile?To be converted to a shapefile, a text file must have x-, y-coordinates, which can be geographic (in decimal degrees) or projected.13. What is COGO?COGO refers to coordinate geometry, a study of geometry and algebra that can provide the methods for creating digital spatial data of points, lines, and polygons from survey data.14. Suppose you are asked to convert a paper map to a digital data set. What methods can you use for the task? What are the advantages and disadvantages of each method?One can convert a paper map to a digital data set by using digitizing or scanning. Digitizing using a digitizing table is simpler because a GIS package typically has a built-in digitizing module for manual digitizing. This method is also preferred if the number of features to be digitized is small. Scanning uses the machine and computer algorithm to do most of the work, thus avoiding human errors caused by fatigue or carelessness. Scanning can also be more cost effective than manual digitizing for a large data producer.15. The scanning method for digitizing involves both rasterization and vectorization. Why?Rasterization converts a black-and-white map into a binary scanned file in raster format. Vectorization uses a process called tracing to turn raster lines into vector lines.16. Describe the difference between on-screen digitizing and tablet digitizing.On-screen digitizing is manual digitizing on the computer monitor. Compared to tablet digitizing, on-screen digitizing is more comfortable for the user. Another advantage of one-screen digitizing is that, during the editing process, the user can consult different data sources displayed on the screen.Chapter 6 Review Questions1. Explain map-to-map transformation.Map-to-map transformation is one type of geometric transformation that converts the newly digitized map into projected coordinates.2. Explain image-to-map transformation.Image-to-map transformation is one type of geometric transformation that converts the rows and columns (i.e., the image coordinates) of a satellite image into projected coordinates.3. An image-to-map transformation is sometimes called an image-to-world transformation. Why?An image-to-map transformation is also called an image-to-world transformation because the process converts a satellite image into real-world coordinates.4. The affine transformation allows rotation, translation, skew, and differential scaling. Describe each of these transformations.Rotation can rotate a map’s x-and y-axis from the origin. Translation can shift its origin to a new location. Skew can allow a nonperpendicularity (or affinity) between the axes, thus changing its shape to a parallelogram with a slanted direction. And differential scaling can change the scale by expanding or reducing in the x and/or y direction.5. Operationally, an affine transformation involves three sequential steps. What are these steps?Step 1: update the x- and y-coordinates of selected control points to real-world coordinates.Step 2: run an affine transformation on the control points and examines the RMS error. Step 3: use the estimated coefficients and the transformation equations to compute the x- and y-coordinates of map features in the digitized map or pixels in the image.6. Explain the role of control points in an affine transformation.The control points are used to estimate the coefficients of the affine transformation and to compute the root mean square (RMS) error. Therefore, the control points play a key role in the transformation process.7. How are control points selected for a map-to-map transformation?Control points are selected directly from the source map. A USGS 1:24,000 scale quadrangle map has 16 points with known longitude and latitude values: 12 points along the border, and 4 additional points within the quadrangle. These 16 points are potential control points for a map-to-map transformation.8. How are ground control points chosen for an image-to-map transformation? Ground control points (GCPs) are selected from a satellite image. GCPs are points where both image coordinates (in rows and columns) and real-world coordinates can be identified.9. Define the root mean square (RMS) error in geometric transformation.The root mean square (RMS)error measures the deviation between the actual (true) and estimated (digitized) locations of the control points. In other words, the RMS error measures the goodness of the control points.10. Explain the role of the RMS error in an affine transformation.The RMS error is a measure of the accuracy of an affine transformation. If the RMS error is within the acceptable range, then the assumption is that this same level of accuracy based on the control points can also apply to the entire map or image.11. Describe a scenario in which the RMS error may not be a reliable indicator of the goodness of a map-to-map transformation.Suppose the control points are located at the four corner points of a USGS quadrangle map. Even if the control points are shifted from their true locations, the RMS error remains unchanged as long as the object formed by the control points retains the shape of a parallelogram.12. Why do we have to perform the resampling of pixel values following an image-to-map transformation?Because the new image created from an image-to-map transformation has no pixel values, resampling must be followed to fill each pixel of the new image with a value or a derived value from the original image.13. Describe three common resampling methods for raster data.Three common resampling methods are nearest neighbor, bilinear interpolation, and cubic convolution. The nearest neighbor resampling method fills each pixel of the new image with the nearest pixel value from the original image. The bilinear interpolation method uses the average of the four nearest pixel values from three linear interpolations. And the cubic convolution method uses the average of the 16。
地下管线三向地震动一致激励与非一致激励数值分析
地下管线三向地震动一致激励与非一致激励数值分析刘飞成;张建经;邓小宁;王志佳【摘要】基于某工业地下管道建立有限元模型,考虑管土相互作用和行波效应,综合分析在三向地震动一致激励与非一致激励下的管道动力响应结果,并且简单分析部分相关因素对管道动力响应结果的影响。
结论如下：对于地下管道来说,非一致激励与一致激励作用下的位移响应曲线在峰值和形状方面存在较为明显的不同,具体表现为：非一致作用水平向位移远大于一致作用,而竖直向位移稍大于一致作用;对于应力响应,不管一致还是非一致激励,同一截面各处的应力响应有明显不同,并且总体来说非一致作用下较大;位于管道走向变化段、土层变化处和管道弯曲段的截面的位移响应峰值和应力响应一般会产生突变,说明这些因素对管道的动力响应具有较为明显的影响。
【期刊名称】《地震工程学报》【年(卷),期】2015(037)002【总页数】7页(P355-361)【关键词】地下管;行波效应;管土相互作用;位移响应;应力响应【作者】刘飞成;张建经;邓小宁;王志佳【作者单位】[1]西南交通大学土木工程学院,四川成都610031;[2]郑州中核岩土有限公司,河南郑州450002【正文语种】中文【中图分类】TV672地下管线，尤其是长距离的地下管线，在当今的土木工程建设中极为普遍。
如果地下管线遇到地震等自然灾害，很容易发生破坏，从而影响到其正常工作，最终会对人们的安全以及生活带来很大的影响。
如1995年日本阪神大地震中神户地区供排水系统主水管网破坏1 610处，导致110万用户断水，一周后仅修复三分之一，100多天后才全部修复，与此同时，该地区供气系统、供电系统也都遭到严重破坏，还导致了次生灾害的发生[1-2]。
2008年5月12日四川汶川8.0级大地震让映秀镇附近位于龙门山断裂带上的居民伤亡惨重，城镇基础设施及房屋遭到了严重破坏，供水、排水、电力、通讯系统全部中断。
所以对于地下管道的抗震研究应该给予重视。