Multi‐process Late Quaternary landscape evolution modelling reveals lags in climate response over small spatial scales     

A. J. A. M. Temme  A. Veldkamp 《地球表面变化过程与地形》2009,34(4):573-589

Landscapes evolve in complex, non‐linear ways over Quaternary timespans. Integrated geomorphological field studies usually yield plausible hypotheses about timing and impact of process activity. Landscape Evolution Models (LEMs) have the potential to test and falsify these landscape evolution hypotheses. Despite this potential, LEMs have mainly been used with hypothetical data and rarely to simulate the evolution of an actual landscape. In this paper, we use a LEM (LAPSUS: LandscApe ProcesS modelling at mUlti dimensions and scaleS) to explore if it is possible to test and falsify conclusions of an earlier field study on 50 ka landscape evolution in Okhombe Valley, KwaZulu Natal, South Africa. In this LEM, five landscape processes interact without supervision: water driven erosion and deposition, creep, solifluction, biological weathering and frost weathering. Calibration matched model results to three types of qualitative fieldwork observations: individual process activity over time, relative process activity over time and net landscape changes over time. Results demonstrate that landscape evolution of the Okhombe valley can be plausibly simulated. A particularly interesting and persistent feature of model results are erosional and depositional phases that lag climatic drivers both by decades, and by several ka within a few hundred meters. The longer lag has not been reported for this spatial scale before and may be an effect of slow landscape‐soil‐vegetation feedbacks. The combined modelling and fieldwork results allow a more complete understanding of these responses to climate change and can fill in hiatuses in the stratigraphical record. Suggestions are made for methodological adaptations for future LEM studies. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Seismic behavior of single‐story asymmetric‐plan buildings under uniaxial excitation     

Andrea Lucchini  Giorgio Monti  Sashi Kunnath 《地震工程与结构动力学》2009,38(9):1053-1070

The critical parameters that influence the nonlinear seismic response of asymmetric‐plan buildings are identified by evaluating the effects of different asymmetries that may characterize the structure of a building as well as exploring the influence of the ground motion features. First, the main findings reported in the literature on both the linear and nonlinear dynamic response of asymmetric‐plan buildings are presented. The common findings and the conflicting conclusions reached in different investigations are pointed out. Then, the results of comprehensive nonlinear dynamic analyses performed for evaluating the seismic response of systems characterized by different strength and stiffness configurations, representative of a large class of asymmetric‐plan buildings, are reported. Findings from the study indicate that the building response changes when moving from the linear to the nonlinear range, so that the seismic behavior of asymmetric‐plan buildings, apart from the source of asymmetry, can be always classified as irregular. Additionally, it was observed that as the seismic demands cause amplification of system nonlinearity with increasing earthquake intensity, the maximum displacement demand in the different resisting elements tends to be reached with the same deformed configuration of the system. The resultant of the seismic forces producing such a maximum demand is located at the center of resistance and corresponds to the collapse mechanism of the system that provides the maximum lateral strength in the exciting direction of the seismic action. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Avulsion regimes in southeast Texas rivers     

Jonathan D. Phillips 《地球表面变化过程与地形》2009,34(1):75-87

Avulsions – relatively sudden changes in course, or establishment of new anabranches – are an important process in alluvial rivers. Their key role in floodplain construction and alluvial architecture, and the general conditions favouring avulsions, are well known. However, avulsion processes and evolution, and the factors controlling avulsion regimes, are poorly understood. In the southeast Texas coastal plain, where avulsions are common features of the river valleys, avulsions were studied on the lower Brazos, Navasota, Trinity, Neches and Sabine rivers using a combination of aerial imagery, digital elevation models and field surveys. Avulsions have important influences on the surface morphology and contemporary processes in all five rivers. Features associated with avulsions are active and distinct throughout the study area, and all the rivers have experienced geologically (if not historically) recent avulsions. However, no two of the study rivers have the same contemporary avulsion regime. First‐order differences in avulsion style are controlled by the stage of valley filling, and within the three rivers characterized by an unfilled incised valley, antecedent morphology associated with late Quaternary and Holocene coastal and fluvial‐deltaic processes accounts for the major differences. In the Navasota (27 avulsions in 185 km) and Neches (21 in 340 km) rivers, subchannels associated with avulsions exist in all stages of development from active to infilled, and some have occurred in recent decades. The other rivers have fewer avulsions, but both the Sabine and Trinity have experienced historic channel shifts. Only the Brazos River has experienced no avulsions within the past c. 300 years. Results show that even within a region of similar environmental controls and geological history local variations in inherited morphology can result in different avulsion regimes. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Improving the inverse compensation method for real‐time hybrid simulation through a dual compensation scheme     

Cheng Chen  James M. Ricles 《地震工程与结构动力学》2009,38(10):1237-1255

Real‐time hybrid simulation combines experimental testing of physical substructure(s) and numerical simulation of analytical substructure(s), and thus enables the complete structural system to be considered during an experiment. Servo‐hydraulic actuators are typically used to apply the command displacements to the physical substructure(s). Inaccuracy and instability can occur during a real‐time hybrid simulation if the actuator delay due to servo‐hydraulic dynamics is not properly compensated. Inverse compensation is a means to negate actuator delay due to inherent servo‐hydraulic actuator dynamics during a real‐time hybrid simulation. The success of inverse compensation requires the use of a known accurate value for the actuator delay. The actual actuator delay however may not be known before the simulation. An estimation based on previous experience has to be used, possibly leading to inaccurate experimental results. This paper presents a dual compensation scheme to improve the performance of the inverse compensation method when an inaccurately estimated actuator delay is used in the method. The dual compensation scheme modifies the predicted displacement from the inverse compensation procedure using the actuator tracking error. Frequency response analysis shows that the dual compensation scheme enables the inverse compensation method to compensate for actuator delay over a range of frequencies when an inaccurately estimated actuator delay is utilized. Real‐time hybrid simulations of a single‐degree‐of‐freedom system with an elastomeric damper are conducted to experimentally demonstrate the effectiveness of the dual compensation scheme. Exceptional experimental results are shown to be achieved using the dual compensation scheme without the knowledge of the actual actuator delay a priori. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

长偶极大功率可控源激励下目标体电性参数的频率响应   总被引：13，自引：6，他引：7       下载免费PDF全文

底青云  王光杰  王妙月  王若 《地球物理学报》2009,52(1):275-280

利用三维（3D）全空间积分方程准线性解作为数值模拟手段,对包含电离层、大气层和地球介质层的“地-电离层”典型异常目标体多层介质模型进行了数值模拟,得到了偶极源长度100 km、电流200 A、收发距离远达1600 km的合理的异常电性目标体的电阻率-频率响应结果.通过对不同埋深异常目标体的电阻率-频率特征的讨论,认为当考虑电离层和大气层的“地-电离层”大尺度深层横向不均匀复杂介质模拟时,电磁场对深部目标体仍有很好的异常响应,但当异常体电阻率及同一电阻率的岩石埋深不同时,其电阻率-频率的响应特征有很大不同,这正反映了不同岩石物性参数的电阻率-频率响应特征.文中结果表明从长偶极大功率源（WEM）激励的电磁场观测资料区分岩石的电阻率参数是可能的,这为利用WEM观测资料建立电性参数和岩石/地层参数经验关系奠定了基础.  相似文献   

黏弹性双相介质参数反演的同伦方法   总被引：4，自引：1，他引：3       下载免费PDF全文

田迎春  章梓茂  马坚伟  杨慧珠 《地球物理学报》2009,52(9):2328-2334

本文以介质的动态时域响应（位移、速度、加速度）作为反演的依据,对黏弹性双相介质的材料参数进行了反分析研究.根据附加条件,并考虑到由于测量误差和测量数据的不充分造成的反演问题的不适定性,将黏弹性双相介质的参数反演问题转化为非线性泛函的极小值问题,然后应用大范围收敛的同伦方法求出使泛函极小的根作为反问题的解.最后,以二维半空间黏弹性双相介质模型为例进行了数值反演分析,数值结果表明本文方法在参数的反演过程中目标函数稳定收敛,且具有一定的抗“噪声”干扰性能;与利用速度和加速度信息反演的结果相比,利用位移信息反演的结果具有较高的精度和抗噪声能力.  相似文献   

裂缝性储层的电各向异性响应特征研究   总被引：8，自引：5，他引：3       下载免费PDF全文

沈金松  苏本玉  郭乃川 《地球物理学报》2009,52(11):2903-2912

以水平裂缝分布的孔隙介质模型为基础,建立了水平裂缝面的平行裂缝分布和带粗糙表面的点接触裂缝模型,导出了两类裂缝模型的水平和垂直电阻率响应关系,分析了两类裂缝模型在没有围压和存在围压条件下的水平电阻率、垂直电阻率变化规律和电各向异性系数的变化特征.讨论了裂缝开度、裂缝密度和裂缝粗糙度等裂缝特征参数对裂缝性储层电各向异性的影响.为简化讨论,所有电性响应特征的分析都忽略了裂缝和孔隙表面的导电性和极化的影响.利用平行分布水平裂缝面模型和带粗糙面的裂缝模型,考察了围压条件下的裂缝性岩石的电各向异性响应特征,得到了对实际应用有意义的结果.  相似文献   

三峡井网井水位对汶川8.0级地震的同震响应特征研究h          下载免费PDF全文

刘成龙  王广才  张卫华  梅建昌 《地震学报》2009,31(2):188-194

系统分析了三峡井网8口井水位对汶川8.0级地震的同震响应及其后效特征,揭示出这些特征因井而异,其差异性在井孔结构相似的条件下主要取决于井点的构造部位、观测含水层的地下水埋藏类型、含水层的导水系数等条件;深入研究了井水位同震后效特征中残留阶升与阶降的力学含义及其地震预测意义,并用仙女山断裂带上近期地震活动验证了残留阶升区可能是未来地震危险区的科学推论．   相似文献   

2009年7月15日新西兰南岛西海岸近海地震破裂过程快速反演     

张勇  许力生  陈运泰 《地震学报》2009,31(6):699-701

用地震破裂过程快速反演方法,在2009年7月15日新西兰南岛西海岸近海地震发生后,采用全球地震台网（GSN）的宽频带地震资料,快速反演了这次地震的破裂过程,并于震后4小时内得出了这次地震破裂过程的反演结果．结果表明,这次新西兰南岛西海岸近海地震的破裂过程具有如下基本特征:① 矩震级约为MW7.8;② 地震主要破裂持续时间约为40s;③ 滑动量在断层面上的分布比较简单,整个地震破裂只包含一个滑动量较大的区域;④ 这次地震基本上是一次单侧破裂事件,破裂主要朝向西南方向．   相似文献   

Analysis on the Characteristics of the Coseismic Response of Water Levels Recorded in Three Wells in Hainan,China to the Two Sumatra-Andaman Strong Earthquakes     

Li Zhixiong  Gu Shenyi  Yuan Xiwen  Liu Wei  Ming Suihu  Yang Guang  Guo Nan 《中国地震研究》2008,22(4):448-459

The characteristics of seismic water level fluctuations of the two Sumatra-Andaman strong earthquakes with magnitude 8.7 and 8.5 on December 26,2004 and March 29, 2005 recorded at Jiaji well, Qionghai, Hainan were analyzed, the features of the infrequent ＂step＂ changes of well water level after the two earthquakes were also analyzed and the mechanism of the ＂step change＂ of well water level was discussed. Then the high-sample-rate digital observation data of seismically-induced water level fluctuations of the Sumatra-Andaman strong earthquakes with magnitude 8.7 and 8.5 recorded at Nanbin well, Sanya and Tanniu well, Wenchang were analyzed. The results suggest that the dominant period of the seismic well water level fluctuation in all three wells was comparatively accordant, the amplitudes of seismic water level fluctuation of the same earthquake in different wells were clearly different, the time duration of seismic water level fluctuations of different earthquakes at the same well was also clearly different.  相似文献