利用声学调查法和沉积柱理化参数评估河道型水库碳埋藏通量

河道型水库对有机碳具有重要的拦截作用,影响内陆水体碳循环。然而,河道型水库水体滞留时间较短,其碳埋藏效应容易被忽视。受野外观测方法的限制,准确地评估河道型水库碳汇潜力面临挑战。声学调查法能够全面反映水库沉积物淤积分布,是一种快速、经济和准确的水库碳埋藏评估方法。本研究采用声学调查法、沉积柱理化参数和碳同位素技术,对乌江流域河道型水库(思林水库)有机碳埋藏开展了调研。结果表明,思林水库沉积物厚度变化范围为0~3.53 m,不规则的水下地形导致沉积物淤积分布具有高度的空间异质性。思林水库沉积物有机碳含量、C/N摩尔比和δ13 C值变化范围分别为1.03%~3.40%、4.62~9.14和-28.5‰~-23.8‰,平均值分别为1.93%、7.24和-26.6‰,显示沉积物有机碳主要来源于水生浮游植物。思林水库内源有机碳对沉积物总有机碳的贡献比例范围为21.2%~85.1%,平均值为60.1%。沉积物内源有机质含量与营养盐氮磷浓度呈显著正相关,表明营养盐氮磷的输入促进了内源有机质的生成。思林水库有机碳埋藏速率变化范围为0~12133.4 g/(m^(2)·a),平均值为1429.8 g/(m^(2)·a),有机碳埋藏通量为2.16×10^(10)g/a,相当于全球水库有机碳埋藏通量的0.36‰,表明河道型水库碳汇潜力不容忽视。思林水库内源有机碳通量为1.30×10^(10)g/a,相当于水气界面CO 2释放通量的0.32倍。本研究水库和其他研究的水库有机碳埋藏速率与水体滞留时间呈对数函数关系,该经验函数将有助于估算全球水库有机碳埋藏速率。

Methods for seismic sedimentology research on continental basins

In contrast to marine deposits, continental deposits in China are characterized by diverse sedimentary types, rapid changes in sedimentary facies, complex lithology, and thin, small sand bodies. In seismic sedimentology studies on continental lacustrine basins, new thinking and more detailed and effective technical means are needed to generate lithological data cubes and conduct seismic geo- morphologic analyses. Based on a series of tests and studies, this paper presents the concepts of time-equivalent seismic attributes and seismic sedimentary bodies and a ＂four-step approach＂ for the seismic sedimentologic study of conti- nental basins： Step 1, build a time-equivalent stratigraphic framework based on vertical analysis and horizontal corre- lation of lithofacies, electrofacies, seismic facies, and pale- ontological combinations; Step 2, further build a sedimentary facies model based on the analysis of single- well facies with outcrop, coring, and lab test data; Step 3, convert the seismic data into a lithological data cube reflecting different lithologies by means of seismic tech- niques; and Step 4, perform a time-equivalent attribute analysis and convert the planar attribute into a sedimentary facies map under the guidance of the sedimentary facies model. The whole process, highlighting the verification and calibration of geological data, is an iteration and feedback procedure of geoseismic data. The key technologies include the following： （1） a seismic data-lithology conversion technique applicable to complex lithology, which can convert the seismic reflection from interface types to rock layers; and （2） time-equivalent seismic unit analysis and a time- equivalent seismic attribute extraction technique. Finally, this paper demonstrates the validity of the approach with an example from the Qikou Sag in the Bohai Bay Basin and subsequent drilling results.

Seismic risk analysis of coastal area of Pakistan

Estimation of seismic hazard for the fast developing coastal area of Pakistan is carried out using deterministic and probabilistic approaches. On the basis of seismotectonics and geology, eleven faults are recognized in five seismic provinces as potential hazard sources. Maximum magnitude potential for each of these sources is calculated. Peak ground acceleration (PGA) values at the seven coastal cities due to the maximum credible earthquake on the relevant source are also obtained. Cities of Gwadar and Ormara with acceleration values of 0.21g and 0.25g respectively fall in the high seismic risk area. Cities of Turbat and Karachi lie in low seismic risk area with acceleration values of less than 0.1g. The Probabilistic PGA maps with contour interval of 0.05g for 50 and 100 years return period with 90% probability of non-exceedance are also compiled.

A phased approach to enable hybrid simulation of complex structures

Hybrid simulation has been shown to be a cost-effective approach for assessing the seismic performance of structures. In hybrid simulation,critical parts of a structure are physically tested,while the remaining portions of the system are concurrently simulated computationally,typically using a finite element model. This combination is realized through a numerical time-integration scheme,which allows for investigation of full system-level responses of a structure in a cost-effective manner. However,conducting hybrid simulation of complex structures within large-scale testing facilities presents significant challenges. For example,the chosen modeling scheme may create numerical inaccuracies or even result in unstable simulations; the displacement and force capacity of the experimental system can be exceeded; and a hybrid test may be terminated due to poor communication between modules(e.g.,loading controllers,data acquisition systems,simulation coordinator). These problems can cause the simulation to stop suddenly,and in some cases can even result in damage to the experimental specimens; the end result can be failure of the entire experiment. This study proposes a phased approach to hybrid simulation that can validate all of the hybrid simulation components and ensure the integrity largescale hybrid simulation. In this approach,a series of hybrid simulations employing numerical components and small-scale experimental components are examined to establish this preparedness for the large-scale experiment. This validation program is incorporated into an existing,mature hybrid simulation framework,which is currently utilized in the Multi-Axial Full-Scale Sub-Structuring Testing and Simulation(MUST-SIM) facility of the George E. Brown Network for Earthquake Engineering Simulation(NEES) equipment site at the University of Illinois at Urbana-Champaign. A hybrid simulation of a four-span curved bridge is presented as an example,in which three piers are experimentally controlled in a total of 18 degrees of freedom(DOFs). This simulation illustrates the effectiveness of the phased approach presented in this paper.

Implications of seismic pounding on the longitudinal response of multi-span bridges-an analytical perspective

Seismic pounding between adjacent frames in multiple-frame bridges and girder ends in multi-span simply supported bridges has been commonly observed in several recent earthquakes.The consequences of pounding include damage to piers,abutments,shear keys,bearings and restrainers,and possible collapse of deck spans.This paper investigates pounding in bridges from an analytical perspective.A simplified nonlinear model of a multiple-frame bridge is developed including the effects of inelastic frame action and nonlinear hinge behavior,to study the seismic response to longitudinal ground motion.Pounding is implemented using the contact force-based Kelvin model,as well as the momentum-based stereomechanical approach.Parameter studies are conducted to determine the effects of frame period ratio,column hysteretic behavior,energy dissipation during impact and near source ground motions on the pounding response of the bridge.The results indicate that pounding is most critical for highly out-of-phase frames and is not significant for frame period ratios greater than 0.7.Impact models without energy dissipation overestimate the displacement and acceleration amplifications due to impact,especially for elastic behavior of the frames.Representation of stiffness degradation in bridge columns is essential in capturing the accurate response of pounding frames subjected to far field ground motion.Finally,it is shown that strength degradation and pounding can result in significant damage to the stiffer frames of the bridge when subjected to large acceleration pulses from near field ground motion records.

Seismological Approaches to Earthquake Prediction

Seismological approaches used in earthquake prediction involve many subjects. To predict large earthquakes from small to moderate foreshocks has a clear meaning in physics. Some of the main methods of earthquake prediction used in China are outlined in this paper. According to the anomalies used for earthquake prediction, seismological approaches can be divided into two groups: those that use the anomalies in seismic patterns, including the increase and decrease in regional seismicity, the appearance of seismic gaps, seismic belts, seismic swarms, and foreshocks and those that use anomalies in special values and in seismic waves, such as the anomalies in b values and f values, in the Vp/VS ratio, Q values, stress drop, and shear stress.

Seismic Hazard Assessment of District Mansehra,Khyber Pakhtoonkhawa,Pakistan

The site of Mansehra is located seismically in an active regime, known as the Crystalline Nappe Zone and Hazara-Kashmir Syntaxis in NW Himalayas, Pakistan. Seismic Hazard Assessment （SHA） for the site has been carried out by considering the earthquake source zones, selection of appropriate attenuation equations, near fault effects and maximum potential magnitude estimation. The Mansehra Thrust, Oghi Fault, Banna Thrust, Balakot Shear Zone, Main Boundary Thrust, Panjal Thrust, Jhelum Fault and Muzaffarabad Fault and, further to the south, the Sanghargali, Nathiagali, and Thandiani Thrusts are the most critical tectonic features within the 50 km radius of Mansehra. Using the available instrumental seismological data from 1904 to 2007, SHA has been carried out. Other reactivated critical tectonic features in the area have been investigated. Among them the Balakot-Bagh fault, with the fault length of 120 km from Balakot to Poonch, has been considered as the most critical tectonic feature on the basis of geological/structural/seismological data. The potential earthquake of maximum magnitude 7.8 has been assigned to the Balakot-Bagh fault using four regression relations. The peak ground acceleration value of 0.25 g （10% probability of exceedance for 50 years） and 0.5 g has been calculated with the help of the attenuation equation using probabilistic and deterministic approaches.

悬臂式挡土墙地震主动土压力计算方法

为确定悬臂式挡土墙立臂的地震主动土压力,针对墙后填土的5种可能失稳破坏模式,基于对数螺旋式滑裂面形态,采用极限分析上限定理与拟静力法推导了作用于假想坦墙背上的地震土压力合力;在此基础上,对坦墙背后滑楔体、立臂与坦墙背之间的土体分别采用斜条分与水平条分法,并通过土压力合力的上限解对坦墙背上的土压应力进行修正,进而求得立臂上的土压力分布。实例分析表明,立臂静土压力沿深度分布呈顶点位于下部的抛物线模式;地震土压力分布一般呈非线性递减模式,计算值与试验值有良好的一致性;两种工况下合力作用点分别位于立臂下半段与上半段。参数分析显示,水平地震影响系数、踵板宽度和立臂倾角的增加均使立臂中上部地震主动土压力显著增大;地震条件下增长踵板宽度会导致立臂受力增加。在强震条件下,本法得到的立臂土压力比铁路规范法的结果高出约9%~14%,立臂底端弯矩更显著高于规范法结果,规范法进行强震条件下悬臂墙的抗震设计可能偏于不安全。

不同结构形式相邻桥联地震响应分析

在高墩大跨连续刚构桥中,引桥部分常采用普通的连续梁桥,相对于高墩大跨连续刚构桥,普通连续梁桥的自振频率较高,导致相邻桥联的动力性能差异较大,连接处在地震作用下可能出现严重破坏。针对上述问题,建立高墩大跨连续刚构桥的有限元模型,考虑与其相连的连续梁引桥,对主桥和引桥及过渡桥墩进行弹塑性动力分析,重点考察相邻桥联连接处的地震表现。分析表明,由于相邻桥梁的动力特性差异巨大,相邻桥联在地震作用下的变形幅值、相位差异巨大,地震作用下高墩大跨连续刚构桥的变形幅值远远超过连续梁桥,相邻桥联的主梁有可能出现撞击,过渡墩上支座也可能出现严重破坏。

地震作用下斜拉桥不同工况碰撞效应研究

研究目的:世界各地地震频发,出于结构抗震性能以及社会和经济效益考虑,需对大跨度斜拉桥的主引桥碰撞问题进行研究,以控制地震破坏程度。研究结论:(1)主引桥间距选值影响主梁残余位移变化;(2)引桥的存在可降低主梁梁端残余位移;(3)周期比、质量比、间距与主桥墩底弯矩和引桥对主桥碰撞做功的相关性分别为88%、91%;对弯矩影响程度由大到小的因素排序是:周期比(75.44%)、质量比(23.13%)、间距(1.43%);对碰撞做功影响最大的是质量比,最小的为周期比,且质量比和间距产生的是正影响,周期比产生的是负影响;(4)通过统计分析分别得到了三种因素与弯矩、碰撞做功之间的线性回归方程;(5)本研究成果可为桥梁抗震设计提供参考。

地震边坡稳定性有限元塑性极限分析拟动力法研究

地震诱发边坡失稳是地震灾害的主要类型之一,开展地震作用下边坡稳定性研究具有重要意义。常规拟静力法无法准确模拟地震波在边坡土体中传播的时间和空间效应,难以真实反映地震荷载。本文采用拟动力法模拟地震动荷载输入,基于塑性极限分析下限定理,结合有限元离散技术,建立了满足静力平衡条件、屈服条件、应力边界条件和间断条件的地震边坡稳定性有限元极限分析下限法数学规划模型,基于内点算法寻求边坡超载系数和安全系数的下限解。通过对典型边坡算例分析,验证了本文方法的正确性。进一步分析了均质土边坡、抗剪强度参数随深度线性增加的非均质土边坡以及双层土边坡的地震稳定性,讨论了关联和非关联流动准则对地震边坡稳定性的影响。结果表明:拟静力法和非关联流动法则会低估地震边坡稳定性;边坡安全系数有限元极限分析下限解与上限解之间的差异小于4.5%,本文方法计算结果接近地震边坡稳定性真解。

考虑第二破裂面的折线墙背挡土墙的地震主动土压力

应用极限平衡原理和库伦土压力思想,研究地震荷载作用下折线墙背挡土墙的主动土压力问题.采用拟动力法对地震荷载进行描述,考虑地震荷载作用下第二破裂面的产生条件,推导折线墙背挡土墙的地震主动土压力计算公式.通过算例分析各参数对折线墙背挡土墙的地震主动土压力的影响,预测墙后填土滑裂面的位置.

基于性态的抗震设计理论和方法的研究与发展

基于性态的抗震设计理论和方法是目前世界各国学术界和工程界广泛关注的课题。本文从性态设 计的理论框架、地震设防水准、结构抗震性态水准、结构抗震设计方法等四方面评述了国内外的研究和 发展状况，并提出了若干值得重视的问题。

碳酸盐岩地震储层学

碳酸盐岩地震储层学是地震储层学的一个分支学科。该文对碳酸盐岩地震储层学的特殊性、研究思路、研究内容、研究方法及针对性关键技术进行了简要论述,并提出碳酸盐岩地震储层学是碳酸盐岩储层油气勘探与开发取得重大突破的关键,将推动碳酸盐岩地区油气勘探的可持续发展。

隔震结构“小震不坏”的动力可靠度分析

本文探讨叠层橡胶隔震体系在"小震不坏"条件下的动力可靠度分析。基于等效线性化的隔震工程设计参数,建立非比例阻尼隔震结构模型。采用双过滤白噪声功率谱模型描述地震动,并用林家浩虚拟激励法进行随机响应分析。以各层的最大层间位移响应作为控制指标,取结构的弹性位移限值作为位移极限值,建立功能状态方程。根据一次二阶矩方法,用串联模式计算体系的总体可靠度。文末选用了一个7层隔震框架作为数值算例,探讨了隔震阻尼、寒冷环境、节点构造误差所引起的隔震层刚度上升,以及场地土类别等对体系动力可靠性的影响。

钢筋混凝土结构基于地震损伤性能的设计

本文结合我国地震设防水准，在国内外有关地震损伤大量研究结果的基础上，提出了钢筋混凝土结构地震损伤的“三水准”性能目标；其次，对于剪切型钢筋混凝土结构，提出了结构层间柱－压弯构件三线性恢复力模型参数确定和地震损伤计算方法；第三，提出了地震损伤直接验算和将地震损伤验算归结为变形验算的钢筋混凝土结构地震损伤性能设计方法；最后，通过设计例题说明了本文方法应用的可行性。

基于性能的抗震设计理论的研究现状及展望

综述了现代抗震设计理论尤其是基于性能的抗震设计理论产生的背景、发展概况和研究内容。基于性能的抗震设计理论和方向是目前世界各国学术界和工程界广泛关注的课题,是抗震设计理念上的一次重大变革。此理论的基础框架已基本形成,但缺乏数据支持,需对指标定量化,使其具有更强的可操作性。

地震作用下大跨度斜拉桥和引桥间碰撞分析

强烈地震作用下大跨度斜拉桥和引桥(一般是简支梁桥或多跨连续梁桥)的纵向振动是耦合的,可能发生碰撞及落梁。采用非线性时程地震反应方法分析了梁端的纵向碰撞效应对体系整体反应的影响,其中对碰撞接触单元的刚度进行了比较分析,然后分别讨论了影响碰撞的几种因素,主要是伸缩缝初始间隙大小、相邻结构周期比等的影响。结果表明碰撞对引桥影响相对较大。

“西气东输”线路勘察中的反射波法及其应用效果

反射波法地震勘探以其采集丰富的地下信息、高分辨率等诸多优点在工程勘察中得到广泛应用。该文结合"西气东输"线路勘察的工程实例,介绍了地震反射波法方法原理与技术,着重突出数据处理的重要性;分析对比了不同参数与方法对处理剖面的影响,确定了地震反射波法资料处理的主要方法和基本流程,特别加强对各CMP道集的速度分析,得到清晰的反射剖面,并给出了综合地层和速度的反射波解释剖面,为工程可行性研究和设计工作提供详细的地质资料和设计参数,取得了良好的勘探效果。

基于模糊层次分析的建筑物单体震害预测方法研究

建筑物的震害预测方法研究对震害防御和震后应急工作有着十分重要的意义,但随着结构类型和抗震规范的不断更新,当前的震害预测理论仍不完善。该文提出了一种基于模糊层次分析的建筑物单体震害预测方法。具体工作如下:1)通过研究一个城市或地区各类房屋建筑的地震易损性,计算得到该城市或地区建筑结构震害指数基准值;2)根据历史地震震害资料和震害预测资料,综合分析影响各类建筑结构震害的主要因素,利用模糊层次分析法计算得到各影响因素权重;3)通过考虑各影响因素中不同影响因子的平均震害指数的变化,得出其对震害指数的影响程度,给出影响因子修正系数;4)采用加权平均法计算得出单体结构震害指数,并给出单体结构破坏等级。利用该方法对汶川8.0级地震中数栋结构进行了验证,其破坏等级同地震现场房屋安全鉴定结果相符。