Similarities between strike-slip faults at different scales and a simple age determining method for active faults

Abstract Several differently scaled strike‐slip faults were examined. The faults shared many geometric features, such as secondary fractures and linkage structures (damage zones). Differences in fault style were not related to specific scale ranges. However, it was recognized that differences in style may occur in different tectonic settings (e.g. dilational/contractional relays or wall/linkage/tip zones), different locations along the master fault or different fault evolution stages. Fractal dimensions were compared for two faults (Gozo and San Andreas), which supports the idea of self‐similarity. Fractal dimensions for traces of faults and fractures of damage zones were higher (D ～1.35) than for the main fault traces (D ～1.005) because of increased complexity due to secondary faults and fractures. Based on the statistical analysis of another fault evolution study, single event movements in earthquake faults typically have a maximum earthquake slip : rupture length ratio of approximately 10^?4, although this has only been established for large earthquake faults because of limited data. Most geological faults have a much higher maximum cumulative displacement : fault length ratio; that is, approximately 10^?2 to 10^?1 (e.g. Gozo, ～10^?2; San Andreas, ～10^?1). The final cumulative displacement on a fault is produced by accumulation of slip along ruptures. Hence, using the available information from earthquake faults, such as earthquake slip, recurrence interval, maximum cumulative displacement and fault length, the approximate age of active faults can be estimated. The lower limit of estimated active fault age is expressed with maximum cumulative displacement, earthquake slip and recurrence interval as T ? (d_max /u) · I(M).     

An attenuation model for distant earthquakes

Large magnitude earthquakes generated at source–site distances exceeding 100km are typified by low‐frequency (long‐period) seismic waves. Such induced ground shaking can be disproportionately destructive due to its high displacement, and possibly high velocity, shaking characteristics. Distant earthquakes represent a potentially significant safety hazard in certain low and moderate seismic regions where seismic activity is governed by major distant sources as opposed to nearby (regional) background sources. Examples are parts of the Indian sub‐continent, Eastern China and Indo‐China. The majority of ground motion attenuation relationships currently available for applications in active seismic regions may not be suitable for handling long‐distance attenuation, since the significance of distant earthquakes is mainly confined to certain low to moderate seismicity regions. Thus, the effects of distant earthquakes are often not accurately represented by conventional empirical models which were typically developed from curve‐fitting earthquake strong‐motion data from active seismic regions. Numerous well‐known existing attenuation relationships are evaluated in this paper, to highlight their limitations in long‐distance applications. In contrast, basic seismological parameters such as the Quality factor (Q‐factor) could provide a far more accurate representation for the distant attenuation behaviour of a region, but such information is seldom used by engineers in any direct manner. The aim of this paper is to develop a set of relationships that provide a convenient link between the seismological Q‐factor (amongst other factors) and response spectrum attenuation. The use of Q as an input parameter to the proposed model enables valuable local seismological information to be incorporated directly into response spectrum predictions. The application of this new modelling approach is demonstrated by examples based on the Chi‐Chi earthquake (Taiwan and South China), Gujarat earthquake (Northwest India), Nisqually earthquake (region surrounding Seattle) and Sumatran‐fault earthquake (recorded in Singapore). Field recordings have been obtained from these events for comparison with the proposed model. The accuracy of the stochastic simulations and the regression analysis have been confirmed by comparisons between the model calculations and the actual field observations. It is emphasized that obtaining representative estimates for Q for input into the model is equally important.Thus, this paper forms part of the long‐term objective of the authors to develop more effective communications across the engineering and seismological disciplines. Copyright © 2003 John Wiley & Sons, Ltd.     

沈阳近百年的温度变化特征及其环流形势分析

沈阳地处全球温度变化的敏感带，在近百年的温度观测记录中，沈阳的温度变化呈逐渐上升之势，近百年增高约1．7℃，这种上升趋势在冬季远比夏季明显。沈阳的年平均温度变化有一个12a的周期，各周期温度基本呈阶梯状上升，20世纪末的周期冬季平均温度比世纪初的周期升温2．8℃左右。从近50a的极端温度的变化趋势来看，极端最低温度明显升高，而极端最高温度并没有上升，变化趋势甚至略下降，以致冬、夏两季温差缩小。从沈阳的最低平均温度和最高平均温度变化来看，两者均随时间逐渐升高，说明沈阳市的增温不仅是最低温度升高造成的，最高温度的增温作用亦十分重要。从冬季环流形势分析来看，东亚大槽及其后弱脊和地面蒙古高压在上世纪80年代、90年代明显减弱，使得冷空气向南侵袭的径向气流减弱，是导致位于冷空气通道中的沈阳冬季增温明显的原因之一。     

辽西医巫闾山地区中生代两期韧性变形的研究

医巫闾山地区的韧性剪切构造是中生代两期韧性变形作用的产物。早期韧性变形中a线理发育,线理走向和糜棱面理走向基本一致,线理在xy面上的侧伏角绝大多数<30°;该期韧性变形是以左行走滑运动为主。晚期韧性变形中a线理发育,线理倾伏向和糜棱岩中糜棱面理倾向相近,线理在xy面上侧伏角主要在45°～90°之间;该期韧性变形是伸展作用的产物。医巫闾山中生代两期韧性剪切变形作用表明,在侏罗纪至早白垩世期间辽西地区不仅发生了强烈挤压推覆作用和伸展作用,也发生了大规模左行走滑作用。该韧性变形作用的发现对进一步研究辽西中生代的构造演化序列、期次和构造格架转换等问题有重要意义。     

某深埋长隧地应力演化及围岩应力位移模拟研究

结合西部地区某深埋长大公路隧道信息化施工 ,对深埋长隧地应力演化及围岩应力位移进行了弹塑性有限元数值模拟研究。研究结果表明 ,隧道轴线现代地应力状况与隧道埋深、地层岩性及构造发育程度有关 ,最大地应力为40 0MPa左右 ;隧道周边围岩应力在曲边墙底部最大 ,约 3 8 0MPa ,隧道开挖引起的围岩应力影响范围约 2 5 0m ;隧道水平收敛和拱顶下沉位移与隧道埋深近于成直线关系。这些研究结果为深埋长隧信息化设计和施工以及围岩稳定性分析提供了科学依据。     

基于梯度塑性理论的岩样在压剪条件下变形及稳定性分析

考虑了正应力及剪应力联合作用在岩样的端部,而且,在正应力被视为变量,剪应力被视为常量这一特殊条件下,对剪切带的变形特征及剪切带-带外弹性体系统的失稳判据进行了分析.根据剪切虎克定律及梯度塑性理论,提出了剪切带内部弹性应变、塑性应变及总应变的解析式,对上述三种应变进行积分,提出了剪切带错动弹性位移、塑性位移及总位移的解析式.利用压缩虎克定律及几何关系建立了剪切带外弹性体的刚度的表达式.根据刚度理论,建立了剪切带-带外弹性体系统的失稳判据.考虑岩样端面的剪切应力后,在流动剪切应力相同时,剪切带内部的弹性剪切应变(均匀分布)将增加;剪切带内部的塑性剪切应变(不均匀分布)将减小;剪切带的弹性剪切位移(线性分布)将增加;剪切带的塑性剪切位移(非线性分布)将减小;剪切带错动位移要小一些.另外,剪切应力对剪切带-带外弹性体系统的失稳判据没有影响.失稳判据仅和岩石的本构参数、剪切带倾角及结构尺寸有关.     

增量位移反分析在水电地下洞室工程中的应用

反分析是确定计算模型参数的有效方法.通常多采用量测所得全量位移进行反演计算.但地下工程中许多量测数据为增量位移,且实际施工过程可以通过建立分步开挖的有限元模型来模拟.据此,结合某水电站地下洞室工程中地下厂房的开挖,建立了模拟动态施工的有限元模型,利用某一开挖步施工前后量测值之差,采用增量位移优化反分析方法对洞室附近初始地应力场及围岩弹性模量进行了反演.计算所得增量位移与实测值符合较好,表明了这种方法的可行性.同时,根据分析结果对该方法进行了评价.     

Effects of Young's modulus on fault displacement

Elastic crack models predict a linear relationship between displacement (u) and rupture (trace) length (L) during slip in a fault zone. Attempts to find universal-scaling laws for L/u, however, have generally failed. Here I propose that these attempts have failed because they do not take into account the changes in the mechanical properties, in particular Young's modulus (stiffness), of the fault zone as it evolves. I propose that Young's modulus affects fault displacement both spatially and temporally: spatially when the trace of a fault at a given time dissects host rocks of different stiffnesses, and temporally when the stiffness of the fault zone itself changes. During the evolution of an active fault zone, the effective Young's modulus of its damage zone and fault core normally decreases, and so does the L/u ratio of the fault. By contrast, during inactive periods sealing and healing of the damage zone and core may increase the stiffness, hence the L/u ratio in subsequent slips. This model predicts that not only will the scaling of L/u within a given fault population vary in space and time, but also that of individual faults. To cite this article: A. Gudmundsson, C. R. Geoscience 336 (2004).     

用L-曲线法确定岭估计中的岭参数

运用L 曲线法来确定岭估计中的岭参数 ,推导了用L 曲线法确定岭参数的基本公式 ,在此基础上实现了其算法 ,并用两个算例 ,比较了新方法和以往方法。结果表明 ,L 曲线法不仅容易收敛 ,而且其计算结果的精度较高