汶川地震区的流变结构与发震高角度逆断层滑动的力学条件

本文利用龙门山地区的地质、地球物理剖面、弹性波速和流变实验数据等,建立了汶川地震相关构造单元的地壳流变结构.川西高原和龙门山构造带的地壳流变结构中存在多个塑性流变层,而四川盆地地壳基本没有出现塑性流变层,这种复杂的流变结构是汶川地震孕育和发生的基础.岩石破裂-黏滑-摩擦实验表明,以二长花岗岩为代表的震源区岩石具有很高的破裂强度和摩擦强度,能够承受极大的差应力和积累巨大的能量,这是高角度逆断层能够滑动和汶川地震强度大的原因之一.高流体压力是高角度逆断层滑动和触发汶川地震的另一个必要条件,而龙门山断层带内可能存在这种比较高的流体压力.     

可变网格与局部时间步长的交错网格高阶差分弹性波模拟

交错网格高阶差分方法是一种在保持效率的前提下提高弹性波模拟精度的有效方法.本文将可变空间网格与变化的时间步长技术引入到交错网格高阶差分弹性波模拟中,提出一种空间网格可任意奇数倍变化与时间步长任意变化的交错网格高阶差分弹性波模拟方法.一系列数值试验表明,该方法能够在保证模拟精度的同时,通过有效降低空间与时间维度上的过采样来显著提高弹性波模拟的效率.同时,该方法还能够精细刻画含孔缝洞介质以及横向变化剧烈介质的局部细微结构,减小弹性波模拟误差,提高介质细微结构处的弹性波传播模拟精度.     

乳山震群震源谱参数的稳健反演

本文引入截止频率f_(max)提出基于Brune模型的高频截止(High-Cut)模型,采用两步反演的方法来拟合求解震源谱的特征参数,并给出其误差范围;实际应用显示该模型的理论谱对观测谱有很好的拟合,可明显改善拐角频率识别的准确度.将该方法应用于2013—2015年的乳山震群,计算了乳山震群25次M_L≥3.0事件的震源参数(地震矩、破裂半径、应力降等),进一步对乳山震群的震源破裂特性进行了讨论.结果显示:拐角频率、应力降与震源尺度大小明显相关;高频衰减系数γ与震源破裂区的复杂程度以及破裂性质有关,当观测记录中混杂有其他事件的波形或微破裂时,高频衰减系数大于2,并且不确定性增大;截止频率f_(max)与地震大小存在一定相关性;使用Beresnev(2001)给出的震源半径计算公式,得到的乳山震群的结果显示与华北地区的经验关系较为一致;乳山震群的应力降明显偏小(最大不超过0.15 MPa),一方面反映了震中区域的构造应力水平,另一方面可能还意味着此次震群是一个相对非耗散型的脆性破裂过程,属于低摩擦应力的断层作用.     

Dynamic responses of structure–soil–structure systems with an extension of the equivalent linear soil modeling

A three-dimensional problem of cross interaction of adjacent structures through the underlying soil under seismic ground motion is investigated. The story shears and lateral relative displacements (drifts) are the targets of the computations. These are calculated using a detailed modeling of soil, the foundations and the two adjacent structures. An equivalent linear behavior is assumed for the soil by introducing reduced mechanical properties consistent with the level of ground shaking for the free-field soil. Then a distinctive soil zone (the near-field soil) is recognized in the vicinity of the foundations where the peak shear strain under the combined effect of a severe earthquake and the presence of structures is much larger than the strain threshold up to which the soil can be modeled as an equivalent linear medium. It is shown that it is still possible to use an equivalent linear behavior for the near-field soil if its shear modulus is further reduced with a factor depending on the dynamic properties of the adjacent structures, the near-field soil, and the design earthquake. Variations of the dynamic responses of different adjacent structures with their clear distances are also discussed.     

高精度温度计在同层水温平行观测中的互相干扰现象

在2015年4月24日一次意外供电故障中,发现宁波地震台高精度温度计在井水温度同层平行观测中有明显的互相干扰现象。认为目前水温观测到的是水井内实际温度与传感器工作时的"升温值"之和,而"升温值"是动态值,其取决于每套仪器的系统特性,一般可能会在0.01℃以上;相互影响可能在0.005℃以上,如果是捆绑式平行观测可能会更高。所以水温测值的波动范围为10~(-4)℃的观测井中,这种干扰不可忽视,并可能影响前兆异常的提取。因此,在水温波动比较小的观测井(泉)中,不主张做同层平行对比观测。最好在一个传感器内安装2套探测温度装置,既免互相干扰,又可相互验证。     

辽宁黑山突发性局地特大暴雨中尺度对流条件和特征

利用常规和加密自动气象站观测资料、卫星和雷达探测资料以及NCEP再分析资料（1°×1°,6h）, 对2013年8 月15-16日辽宁黑山地区特大暴雨的中尺度对流条件和对流系统特征进行探讨。结果表明: 此次强降水由中-β尺度系统引起,短时大暴雨发生在能量舌边缘,地面偏东风和地形强迫抬升作用造成对流单体沿着山脉东侧生成、发展和移动,最终导致持续性对流性强降雨。东北低压冷锋前所激发的中尺度切变和涡旋触发了局地大暴雨。黑山地区上游有两个对流单体生成,向东移动合并影响该地区,移动方向前侧的斜升气流和低质心回波提高了降水效率。     

Assessment of railway vibrations using an efficient scoping model

Vibration assessments are required for new railroad lines to determine the effect of vibrations on local communities. Low accuracy assessments can significantly increase future project costs in the form of further detailed assessment or unexpected vibration abatement measures.This paper presents a new, high accuracy, initial assessment prediction tool for high speed lines. A key advantage of the new approach is that it is capable of including the effect of soil conditions in its calculation. This is novel because current scoping models ignore soil conditions, despite such characteristics being the most dominant factor in vibration propagation. The model also has zero run times thus allowing for the rapid assessment of vibration levels across rail networks.First, the development of the new tool is outlined. It is founded upon using a fully validated three dimensional finite element model to generate synthetic vibration records for a wide range of soil types. These records are analysed using a machine learning approach to map relationships between soil conditions, train speed and vibration levels. Its performance is tested through the prediction of two independent international vibration metrics on four European high speed lines and it is found to have high prediction accuracy.A key benefit from this increased prediction accuracy is that it potentially reduces the volume of detailed vibration analyses required for a new high speed train line. This avoids costly in-depth studies in the form of field experiments or large numerical models. Therefore the use of the new tool can result in cost savings.     

Permanent deformation estimates of dynamic equipment foundations: Application to a gas turbine in granular soils

Permanent displacements of a gas turbine founded on a fine, poorly graded, and medium density sand are studied. The amplitudes and modes of vibration are computed using Barkan´s formulation, and the “High-Cycle Accumulation” (HCA) model is employed to account for accumulated deformations due to the high number of cycles. The methodology is simple: it can be easily incorporated into standard mathematical software, and HCA model parameters can be estimated based on granulometry and index properties. Special attention is devoted to ‘transient’ situations at equipment´s start-up, during which a range of frequencies – including frequencies that could be similar to the natural frequencies of the ground – is traversed. Results show that such transient situations could be more restrictive than stationary situations corresponding to normal operation. Therefore, checking the stationary situation only might not be enough, and studying the influence of transient situations on computed permanent displacements is needed to produce a proper foundation design.     

西藏高海拔地区地震现场应急探讨

介绍了高海拔对人体的主要影响,强调在高海拔地区开展地震应急工作应注意的事项以及应急装备的要求,对进入藏区顺利开展地震应急工作面临的问题和困难提出了相应的对策。     

新型框架结构弹塑性地震反应的等效线性化方法研究

等效线性化方法是计算结构弹塑性地震反应的实用方法.通过对几种等效线性化方法的比较分析,提出了基于FEMA440 （2005）计算等效刚度和等效阻尼比的等效线性化方法;分别采用静力弹塑性分析方法和等效线性化方法,分析了局部使用高性能纤维增强混凝土新型框架结构的弹塑性地震反应.结果表明,两种方法所得结构的地震反应均比较接近.因此,本文建议的等效线性化方法能够较好地预测新型框架结构的弹塑性地震反应.