An isolation system for limited seismic gaps in near‐fault zones

The ability of a recently proposed seismic isolation system, with inherent self‐stopping mechanism, to mitigate or even eliminate seismic pounding of adjacent structures is investigated under severe near‐fault earthquakes. The isolation system is referred to as roll‐in‐cage (RNC) isolator. It is a rolling‐based isolator that provides in one unit the necessary functions of vertical rigid support, horizontal flexibility with enhanced stability, hysteretic energy dissipation, and resistance to minor vibration loads. In addition, the RNC isolator is distinguished by a self‐stopping (buffer) mechanism to limit the bearing displacement under excitations stronger than a design earthquake or at limited seismic gaps, and a linear gravity‐based self‐recentering mechanism to prevent permanent bearing displacement without causing vertical fluctuation of the isolated structure. A previously developed multifeature SAP2000 model of the RNC isolator is improved in this paper to account for the inherent buffer mechanism's damping. Then, the effectiveness of the isolator's buffer mechanism in limiting peak bearing displacements is studied together with its possibly arising negative influence on the isolation efficiency. After that, the study investigates how to alleviate or even eliminate those possibly arising drawbacks, due to the developed RNC isolator's inner pounding as a result of its buffer activation, to achieve efficient seismic isolation with no direct structure‐to‐structure pounding, considering limited seismic gaps with adjacent structures and near‐fault earthquakes. The results show that the RNC isolator could be an efficient solution for aseismic design in near‐fault zones considering limited seismic gaps. Earthquake Engineering and Structural Dynamics. Copyright © 2014 John Wiley & Sons, Ltd.     

中条山北麓断裂中南段全新世地震事件的初步研究

通过对中条山北麓断裂进行探槽研究,揭露了全新世以来,断裂中段和南段的3次古地震事件,包括1次发生在8 570~8 010a BP、贯通断裂中段和南段的8级以上特大地震,以及4 800~6 010a BP和2 110~320a BP发生的2次7级左右的大地震,地震复发间隔约为3 500a。研究表明,中条山北麓断裂的南段和中段在全新世发生过多次活动,活动性较强。     

褶皱陡坎中相关断层在缩短量计算中的作用——以东秋里塔格背斜为例

通过对东秋里塔格背斜地区内与褶皱陡坎伴生的次级断层进行的地质调查,确定了该次级断层属于伸出向斜的逆冲断层,也给出了次级断层的发生时间晚于褶皱作用起始时间的1个变形实例。褶皱陡坎中发育的次级断层使得陡坎上盘地层沿断层面整体向上迁移,不仅次级断层使得阶地面发生掀斜并增大褶皱陡坎的坡度,而且直接影响了区域缩短增量计算的真实性。计算结果显示,当不考虑次级断层对褶皱陡坎高度的影响时,计算所得缩短增量为51.42m,考虑次级断层对褶皱陡坎高度的影响时,计算得到的地壳缩短量为45.23m。二者相差6.19m,偏差占总缩短增量的13.7%,是一个不可忽视的量值。东秋里塔格背斜北翼和南翼的褶皱陡坎发育于相同岩性的基岩中而且具有相同的形成机制。但是背斜北翼在水平距离不足300m的范围内发育了3级褶皱陡坎,这表明北翼相对于南翼,其活动枢纽带更为紧闭。这是由于北翼存在更加强烈的挤压应力及更加快速的隆升作用。因此,次级断层的研究对于正确认识区域构造演化、了解褶皱与断层相互作用关系具有重要意义。但是仍存在很多问题:1)受观察剖面范围有限、次级断层分布不连续和断距沿延伸方向不断增大等因素的制约,次级断层对缩短增量造成的影响可能被低估,计算结果应为缩短量的最小值。2)次级断层增加的陡坎高度与断层的断距、倾角具有怎样的定量关系?3)若次级断层只发育于活动枢纽带内,又会产生怎样的影响?这些问题还需更多的研究实例来进行更加深入的研究。     

significance of high-resolution loess stratification based on grain size and magnetic susceptibility analysis to paleo-earthquake study: a case study of dongyugou loess section,at hongtong,shanxi province

As an important technology to paleoseismologic research, trenching has been used to identify paleo-earthquakes recorded in strata, combined with dating technology. However, there have been some bigger uncertainties and limitations. For instance, subtle strata in loess sediment cannot be interpreted only by naked-eye, which seriously affects identifying paleo-earthquake horizon and time. Therefore, how to improve the accuracy and reduce the uncertainty of paleo-earthquake identification is the important problem we are currently facing. Dongyugou loess section, located in the northeastern corner of Linfen Basin, Shanxi Province, cuts across the Huoshan piedmont fault. The section exposes not only the well-developed loess sequence, but also several obvious faulting events. Thus, this loess section is a better site to make a high resolution study to improve the accuracy and reduce the uncertainty of paleo-earthquake identification. Based on the high-resolution grain size and magnetic susceptibility analysis, and associated with visual interpretation by naked-eye, we made a high-resolution stratification of Dongyugou loess section, including high-resolution thickness of each stratum and its upper and bottom boundaries. Based on the high-resolution stratification and their comparison between two fault walls, we identified three earthquake events, which occurred after formation of u5-7, u4 and u2, corresponding to their stratification depth of 7.1m, 4.7m and 2.9m in hanging wall. Based on results of OSL dating and average sedimentation rate of hanging wall, we estimated that the three events occurred around 45.8ka(between (48.1±1.5)～(43.2±2.5)ka), 32.8ka(between (35.0±2.4)～(30.6±1.3)ka) and 23.3ka(between (26.4±0.8)～(20.9±0.7)ka). According to the thickness difference of three loess-paleosol sedimentary cycles between two fault walls, we calculated the coseismic vertical displacements of the three events as 0.5m, 0.4 and 1.3m, respectively. Compared with other segments of the Huoshan piedmont fault zone, we found the southernmost segment is the weakest, with longer recurrence interval of about 11ka and lower vertical slip rate of 0.048mm/a. The high-accuracy grain size and magnetic susceptibility analysis offers an effective method for reducing the uncertainties of the paleo-earthquake research in loess area.     

铅垂断层向错引起的地表重力变化

利用直立长方体组合模型以及坐标旋转理论,对铅垂断层向错引起的重力变化进行数值模拟,分别计算深度为1、5、10 km的铅垂断层在单一方向上、两个方向上向错引起的地面重力变化。结果表明,当断层在单一方向产生向错时,以左端点为基点的W1、W2向错引起的地面重力变化场均呈现以断层为轴线的对称分布|以中点为基点的W3向错引起的地面重力变化场构成四象限反对称分布。当断层在两个方向上同时产生向错时,以左端点为基点的W1W2向错引起的地面重力变化场呈现以断层为轴线的对称分布,整体显示W2向错起主导作用|以中点为基点的W2W3向错引起的地面重力变化场呈现非对称分布,整体也显示出W2向错起主导作用,断层附近的扭错现象为W3向错的作用。随着断层深度的增加,断层向错引起的地面重力变化值递减,但影响范围逐渐扩大。     

向错-位错组合模型模拟渭河盆地地壳水平变形特征

基于向错-位错组合模型模拟渭河盆地内主要断层的滑动与转动运动变形,通过数值计算获得断层滑动及转动变形引起的地表水平位移,并与盆地内实测GPS水平位移进行了对比。结果表明:采用向错-位错组合模型能够完整地描述断层实际的滑动与转动运动变形状态,组合模型模拟断层滑动与转动引起的地表水平位移与实测GPS水平位移,无论在量级或是运动趋势上均具有较好的一致性特征。     

怀安盆地北缘断裂东段土壤气体地球化学特征

活动断裂带的土壤气体地球化学测量在活动断裂危险性评价方面起着重要作用。 本文讨论了怀安盆地北缘断裂东段的土壤气体地球化学特征及其构造意义。 我们于2012年7月和2013年6月在怀安盆地北缘断裂东段的羊窖沟以及张家窑两地现场测量了土壤气体组分的浓度和通量。 测量结果表明: ① 断裂带土壤气H₂、 Rn、 CO₂和Hg浓度空间分布曲线呈现双峰模式, 且断裂下盘土壤气的Rn、 CO₂和Hg浓度较上盘的高; H₂、 Rn、 CO₂和Hg浓度平均值分别是4.61 ppm、 4.81 k Bqm^-3、 0.38%和9 ngm^-3; 土壤气Rn和CO₂的通量平均值分别是6718 Bqm^-2d^-1和49.83 gm^-2d^-1; ② 土壤气Rn和CO₂在两个测区脱气强烈, 羊窖沟地区土壤气CO₂、 Rn和Hg浓度平均值以及土壤气Rn和CO₂通量值较张家窑地区高。 这些结果可能是两个测区断裂活动性差异引起的。     

鄂尔多斯盆地北部泊尔江海子断裂对上古生界天然气成藏的控制

为了揭示泊尔江海子断裂对鄂尔多斯盆地北部杭锦旗地区上古生界天然气成藏的控制作用,应用地震和钻井资料,在断裂活动性分析的基础上,根据断层泥比率和断层连通概率法对泊尔江海子断裂的侧向和垂向封闭性进行半定量评价,探讨断裂和天然气富集区的关系。结果表明：泊尔江海子断裂呈现3次明显的活动高峰期,分别为加里东期-早海西期的断裂形成期、印支期-早燕山期的挤压逆断裂活动期、中晚燕山期的走滑撕裂活动期,而中晚燕山期的走滑撕裂控制了上古生界天然气主要成藏期。断裂的封闭性具有“横向分段、纵向分层”的特点;横向上,以断层泥比率(SGR)等于0.3为界将泊尔江海子断裂分为侧向优势输导区和侧向封闭区;纵向上,在石千峰组和上石盒子组断裂启闭系数基本都小于1.0,断裂垂向封闭,在下石盒子组和山西组断裂启闭系数主要集中在4.0~10.0,断裂垂向开启。在断裂侧向优势输导区,断裂南部主力烃源区生成的天然气,经断裂发生垂向和侧向运移,易在断裂北部地区富集成藏;在侧向封闭区,则易在断裂南部地区富集成藏。     

利用区域宽频带数据反演鲁甸MS6.5级地震震源破裂过程

基于有限断层模型反演方法,我们利用区域宽频带数据反演得到了2014年8月3日鲁甸M_S6.5级地震的震源破裂过程.反演结果显示：此次地震的发震断层走向为北北西向,破裂主要以左旋走滑为主,位移主要发生在震源左上方,最大滑动量为0.7 m,模型显示断层破裂可能接近地表,破裂长度约10 km.此次地震释放的标量地震矩为1.97×10¹⁸ N·m,相当于矩震级为M_w 6.1,地震能量主要在前15 s释放.鲁甸地震有四个显著的特点：（1）位移主要集中在浅部,从11 km起破点开始迅速向上传播,大部分位于10 km以上且最大位移位于深度3 km处,从模型来看,破裂可能接近地表,因此地表震动较为强烈;（2）应力降比较大,计算显示释放的同震静态应力降约为2.8 MPa;（3）破裂速度较快,在地表附近超过了2.5 km·s^-1;（4）主震可能发生在一个共轭断层系上.这四个特点可能是导致此次地震造成如此重大人员伤亡和财产损失的最重要的原因.     

鲁甸6.5级地震发震断层判定及其构造属性讨论

鲁甸6.5级地震是川滇菱形块体南南东向运动在青藏高原东缘与华南地块相互作用边界变形带上发生的一次中等强度地震.尽管野外应急科学考察没有发现明显的地震地表破裂带,但云南昭通防震减灾局局域地震台网记录到的余震条带状分布、震后科学考察获得的地震烈度长轴方位和极震区地震裂缝等显示出发震断层为NW向包谷垴-小河断裂,左旋走滑性质,属大凉山断裂南端部组成部分;库仑应力计算表明,鲁甸地震可对周边活动断层系历史地震空段产生应力加载作用,其地震危险性不容忽视.