SV波入射下河谷地形地震动分布特征分析

基于显式有限元方法和人工透射边界,对二维河谷地形在3条地震动波以SV波形式垂直入射和30°斜入射下进行了地震反应分析,比较了河谷地表各观测点地震动的差别,探讨了河谷地形地震动空间分布特征。结果表明,河谷地形对地震动分布具有重要影响,沿河谷斜坡顶到谷底的各观测点地震动峰值加速度（PGA）存在显著差异,地震动位移存在差动现象,地震动加速度反应谱在大于1 Hz的高频段差别明显。入射角度是影响场地地震反应的重要因素,斜入射时各观测点PGA和相对位移的离散程度明显大于垂直入射情形。     

岩性及岩体结构对斜坡地震加速度响应的影响

斜坡岩体的岩性及岩体结构是斜坡在地震作用下产生变形破坏的主要控制因素。基于振动台模型试验,对4个斜坡模型探讨了这2个因素对斜坡地震动力响应的影响。岩性包括强度相对较高的硬岩和强度相对较低的软岩,对这两种岩性的斜坡又分别考虑了不含结构面的均质斜坡和含水平层状结构面的斜坡。基于传感器采集到的大量数据,以主频相近的天然地震波和10 Hz正弦波加载为分析工况,获得了以下几点认识：（1）4个模型斜坡坡面和坡内的水平向加速度均具有高程放大效应,尤其是软岩斜坡坡顶放大效应最显著;（2）软岩斜坡对水平向加速度的高程放大效应强于硬岩斜坡,尤其是在均质斜坡中表现最显著,均质软岩斜坡的高程放大效应呈现出明显的非线性特征;（3）当加载方向与水平层面平行时,含水平层状结构面的斜坡比均质斜坡产生了更强的高程放大效应,且在软岩斜坡中体现最显著;（4）岩性差异对斜坡水平向加速度高程效应的影响比结构差异的影响更为显著。研究结果为岩质斜坡的抗震设计提供了一定参考。     

Analysis on mechanism of landslides under ground shaking: a typical landslide in the Wenchuan earthquake

A high steep rock hill with two-side slopes near National Road 213 is used as a prototype in this paper. The full process from initial deformation to sliding of the slope during ground shaking is simulated by a new discrete element method—continuum-based discrete element method. Then, the seismic responses of a high steep rock hill with two-side slopes are researched from the base of time, frequency and joint time–frequency domain using Hilbert–Huang transform and Fourier Transform. The findings are: first, the stress concentration phenomenon occurs at the top of the sliding mass, and then some tension and shear failure points appear, which expand from the top toward the toe of the sliding mass along the structural plane. At the same time, the number of tension failure points gradually increases. Then the toe of the sliding mass fails, and shears out from its toe which results in the landslide. If the material parameters are under the same conditions, the landslide in the middle of the slope occurs before that at the foot of slope, and the starting time of landslide and the arrival time of the peak ground acceleration are synchronous or the former slightly lags behind the latter. The difference of distribution and dissipation of earthquake energy in the sliding body and sliding bed is the major influence factor to induce the landslide. When the accelerations are small, the instantaneous frequency of accelerations between sliding bed and sliding body is generally consistent, the energy transmittance coefficients of the sliding structural plane and the controlled frequency band of the energy all range in a limitation; with the increase of the seismic intensity, the instantaneous frequency and the energy transmittance coefficients gradually decrease, and then they are steady within the lower limitation. At the same time, the controlled frequency band also shifts gradually from high frequency band to the lower one. Based on the input seismic wave, the peak acceleration amplifies as the increase of elevation, regardless of the monitoring points on the steep slope, gentle slope side or inside of the slope. Generally speaking, amplification of the vertical peak acceleration is stronger than that of the horizontal peak acceleration, and amplification of the peak acceleration on a steep slope is stronger than that on a gentle slope, and that of inside of the slope is the weakest amplification.     

Evaluation of local site effects on earthquake damages of Fatih Mosque

Fatih Mosque and its Kulliye (complex) are one of the most important historical monuments in Istanbul. Since it has been built between 1463 and 1470, Fatih Mosque had been subjected to nine strong earthquakes and suffered various degrees of structural damage at every case, including the latest August 17, 1999 Kocaeli Earthquake (M_w = 7.4, epicentral distance approximately 100 km). Recently, a project has been initiated first to study the possible causes of earthquake damage and then develop retrofitting and strengthening techniques to protect this invaluable monument from further damages in the future earthquakes. As part of this investigation, local site soil conditions had been determined and site behavior during earthquakes had been studied in detail. In this paper, the results of 1-D site response analysis, which included convolution and deconvolution analyses utilizing the strong ground motions recorded during the August 17, 1999 Kocaeli Earthquake are presented. The results of the analyses had demonstrated the considerable degree of site amplification, compatible with the recorded motions and the damage suffered. The expected site behavior during a probable future earthquake is also studied using a site specific simulated bedrock motion, and earthquake parameters to be used in dynamic structural analysis are estimated.     

重庆小南海滑坡形成机制离散元模拟分析

重庆小南海滑坡是烈度相对较低地区发生的地震高位滑坡,其成因一直令人费解。基于重庆黔江小南海相关研究资料,通过对复原的小南海坡体进行失稳分析,计算得出使岩体产生崩滑破坏的地震力临界条件,即只有当地震波地形放大后滑坡才能启动。为了进一步验证计算所得的结论,运用UDEC软件建立小南海典型二维场地模型,施加相应的地震力对坡体失稳崩滑的全过程进行模拟,以研究地震作用下地形放大效应触发具平行坡面陡倾控制性结构面的高位岩质斜坡地震机理。研究结果表明,在地震波传播过程中,具平行坡面陡倾控制性结构面的高陡突出地形对地震波有明显的放大作用。该坡体运动模式为：峰值加速度放大-增加的振幅迫使岩体顺平行坡面陡倾控制性结构面迅速拉裂-沿缓倾层面滑移-高速脱离滑源区-巨大的势能和动能驱动坡体做长距离运动,其间伴随解体、颗粒间相互碰撞、铲刮作用,具有二相甚至三相流体性质。分析揭示地震力作用下斜坡体中质点加速度具有地形放大效应。对比结构面监测点和基岩监测点加速度放大系数,表明,滑坡启动时具有较大的加速度,当遇到平行坡面的不连续结构面时,斜坡动力响应强烈,最终导致坡体失稳。     

Landslides induced by the April 2007 Aysén Fjord earthquake, Chilean Patagonia

On the 21st of April 2007, the Aysén Fjord earthquake (Mw 6.2) in southern Chile (45.3° S, 73.0° W) triggered hundreds of landslides in the epicentral area along the fjord coast and surroundings. Some of these landslides induced large tsunami waves within the fjord causing fatalities and damaging several salmon farms, the most important economic activity of the area. The landslides included rock slides and avalanches, rock falls, shallow soil and soil–rock slides, and debris flows. The earthquake was the climax of a seismic swarm that began 3 months earlier. The seismicity is associated with tectonic activity along the Liquiñe–Ofqui fault zone (LOFZ), a major structural feature of the region. The earthquake-induced landslides were mapped and classified from field observations and remote sensing analysis. The landslide areas and epicentral distances are within the expected range for the earthquake magnitude according to worldwide data, while the position of landslides on the slopes strongly suggests topographic amplification effects in triggering the failures. The location of the landslides is also clearly related to some of the main fault branches of the LOFZ. The seismic event has configured a new situation of seismic and landslide hazard in the Aysén region and along the LOFZ, where the presence of towns and economic infrastructure along the coasts of several fjords constitutes a potential risk that was not considered before this seismic event.     

浅切割的高山峡谷复杂地形的地震动放大效应研究

高山峡谷复杂地形是我国西部地区常见的地形和场地条件,大量的工程(桥梁、大坝等)修建在这类场地上.实际震害调查结果表明不规则地形对地震动具有明显的放大作用,对边坡的稳定性和建筑物的安全性构成不利的影响.因此研究高山峡谷复杂地形的地震动放大效应具有重要的工程价值.本文针对浅切割的高山峡谷复杂地形(山体顶和峡谷底的高差在10...     

地震作用下黄土斜坡失稳及运动过程的离散元模拟

在山区,地震诱发滑坡造成的人员伤亡往往占到地震总伤亡人数的一半以上,尤其是在黄土地区,由于地震造成的黄土滑坡具有运动距离远等特征,其灾难性更严重。针对地震诱发黄土斜坡的失稳峰值加速度、临界位移和运动距离等问题,本文利用离散元（PFC）方法,通过对室内三轴实验的应力-应变曲线进行标定和高精度航拍三维地形数据进行转化,以宁夏海口村黄土斜坡为研究对象,开展三维地震作用下斜坡失稳破坏和运动过程的数值模拟研究。通过监测不同位置在地震作用下的应力分量,计算监测点的p、q值并与室内三轴实验所得到p-q破坏线进行比较,获得斜坡破坏过程中的应力路径。结合颗粒的监测位移,获得斜坡失稳破坏的临界位移,得出该黄土斜坡失稳峰值加速度为0.135 g,临界位移为50 cm。同时根据不同地面环境条件,预测了在不同摩擦系数下斜坡失稳后的危害范围,为黄土地区边坡工程的抗震设计及防震减灾工作提供一种新的可视化方法。     

堆积层滑坡地震动力响应的物理模型试验

以玉树7.1级地震诱发的玉树机场路堆积层滑坡为对象,该滑坡坡度约为10o,长×宽×厚为317 m×482 m×19.8 m,由以碎石土为主的上覆层、卵石土为主的滑动带及基岩3层组成,开展大型振动台模型试验,探究震后边坡再次承受振动荷载的能力以及地震垂直分量对坡体稳定性的贡献,分析其动力响应特征和失稳破坏机制。结果表明,强震作用下堆积层滑坡的永久变形是造成地震地质灾害的重要因素;随着输入地震荷载增大,坡脚率先破碎沉降,坡体中部产生弧形裂隙并产生沉降,坡顶出现贯穿张裂隙和剪切裂隙并向坡腰推进,表现出典型的牵引性滑坡特征;峰值加速度(PGA)、动土压力以及加速度频谱与输入地震波的强度、滑坡高程呈正相关;PGA放大系数呈现出明显的非线性特征,其变化趋势随地震荷载强度增大而减小,地震波垂直分量对滑坡PGA放大系数影响略大于水平分量。     

The characteristics and failure mechanism of the largest landslide triggered by the Wenchuan earthquake, May 12, 2008, China

Strong earthquakes are among the prime triggering factors of landslides. The 2008 Wenchuan earthquake (M _w = 7.9) triggered tens of thousands of landslides. Among them, the Daguangbao landslide is the largest one, which covered an area of 7.8 km² with a maximum width of 2.2 km and an estimated volume of 7.5 × 10⁸ m³. The landslide is located on the hanging wall of the seismogenic fault, the Yingxiu–Beichuan fault in Anxian town, Sichuan Province. The sliding mass travelled about 4.5 km and blocked the Huangdongzi valley, forming a landslide dam nearly 600 m high. Compared to other coseismic landslides in the study area, the Daguangbao landslide attained phenomenal kinetic energy, intense cracking, and deformation, exposing a 1-km long head scarp in the rear of the landslide. Based on the field investigation, we conclude that the occurrence of the landslide is controlled mainly by the seismic, terrain, and geological factors. The special location of the landslide and the possible topographic amplification of ground motions due to the terrain features governed the landslide failure. The effects of earthquakes on the stability of slopes were considered in two aspects: First, the ground shaking may reduce the frictional strength of the substrate by shattering of rock mass. Second, the seismic acceleration may result in short-lived and episodic changes of the normal (tensile) and shear stresses in the hillshopes during earthquakes. According to the failure mechanism, the dynamic process of the landslide might contain four stages: (a) the cracking of rock mass in the rear of the slope mainly due to the tensile stress generated by the ground shaking; (b) the shattering of the substrate due to the ground shaking, which reduced the frictional strength of the substrate; (c) the shearing failure of the toe of the landslide due to the large shear stress caused by the landslide gravity; and (d) the deposition stage.     

A seismic landslide hazard analysis with topographic effect,a case study in the 99 Peaks region,Central Taiwan

It has been known that ground motion amplitude will be amplified at mountaintops; however, such topographic effects are not included in conventional landslide hazard models. In this study, a modified procedure that considers the topographic effects is proposed to analyze the seismic landslide hazard. The topographic effect is estimated by back analysis. First, a 3D dynamic numerical model with irregular topography is constructed. The theoretical topographic amplification factors are derived from the dynamic numerical model. The ground motion record is regarded as the reference motion in the plane area. By combining the topographic amplification factors with the reference motions, the amplified acceleration time history and amplified seismic intensity parameters are obtained. Newmark’s displacement model is chosen to perform the seismic landslide hazard analysis. By combining the regression equation and the seismic parameter of peak ground acceleration and Arias intensity, the Newmark’s displacement distribution is generated. Subsequently, the calculated Newmark’s displacement maps are transformed to the hazard maps. The landslide hazard maps of the 99 Peaks region, Central Taiwan are evaluated. The actual landslide inventory maps triggered by the 21 September 1999, Chi-Chi earthquake are compared with the calculated hazard maps. Relative to the conventional procedure, the results show that the proposed procedures, which include the topographic effect can obtain a better result for seismic landslide hazard analysis. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

基于Newmark模型的概率地震滑坡危险性模型参数优化与应用:以鲁甸地震区为例

应用概率地震危险性评价模型进行地震滑坡危险性区划,是解决潜在地震诱发滑坡危险性评价中震源不确定性与诱发滑坡时空不确定性的有效方法 .通过理论分析,结合鲁甸地震区的实际情况,对基于力学原理的Newmark滑块位移模型与概率地震滑坡危险性分析方法中的参数的不确定性问题进行了分析,将斜坡岩土体地震作用下的强度衰减效应、地震加速度地形放大效应、断层破碎带效应融合到了斜坡累积位移计算模型中,进行了模型计算参数的优化.改进后的分析模型,更好地反映了高陡斜坡地形与断层破碎带对地震滑坡灾害发育的控制作用,在鲁甸地震区域滑坡应用中,优化模型中的滑坡失稳极高风险区与实际地震滑坡分布表现出了较好的一致性,在超越概率2%的滑坡失稳概率分布中,鲁甸地区包谷垴-小河断裂、鲁甸-昭通断裂带及牛栏江河谷地带地震滑坡高-极高风险区分布面积增幅十分显著.因此,在Newmark滑块位移模型中考虑地震动参数与岩土参数动态响应规律与变量间的定量关系,对于提高区域斜坡稳定性分析的可靠性具有重要意义.     

锚固岩石边坡地震稳定性拟动力分析

地震易发地区的锚固岩石边坡,需要研究其地震稳定性。对于锚固典型岩石边坡,在考虑水平与竖向地震力、张裂缝积水深度、坡顶超载、锚索倾角、锚索位置、锚索拉力及静水与动水压力等的条件下,运用拟静力和拟动力方法分别推导了不同工况条件下其抗滑和抗倾覆地震安全系数。分析表明,竖向向上地震力有利于锚固岩石边坡的抗滑稳定,而竖向下的地震力有利于锚固岩石边坡的抗倾覆稳定;在相同工况条件下,当岩体放大系数等于1.0时,拟动力与拟静力方法所得锚固岩石边坡地震安全系数相差无几,但是,当岩体放大系数逐渐增大时,拟动力方法所得地震安全系数越来越明显地小于拟静力方法所得地震安全系数。因此,在抗震设计当中适当的考虑岩体放大系数,将会有利于锚固岩石边坡的安全设计。     

多点、多向地震作用下非圆弧滑面边坡稳定分析通用条分法

在地震边坡稳定性分析当中,往往采用单点地震动输入,但实际地震动是随着时间和空间变化的。为了研究边坡在多点、多向地震作用下的稳定性,地震动输入采用考虑地震动的空间时间变化特性的人工合成多点、多向地震动,并将之转化为作用于边坡上的多点、多向地震荷载,在陈祖煜院士所提出的通用条分法的基础之上,推导了适用于任意形状滑面、即满足力的平衡又满足力矩平衡的多点、多向地震作用下边坡稳定通用条分法的极限平衡微分方程,并给出了求解动力安全系数的方法,通过两个算例验证了方法的可行性。     

同震滑坡发生概率研究——新一代地震滑坡危险性模型

地震滑坡发生真实概率研究基本空白。本研究创新性的利用贝叶斯概率方法与机器模型开展了中国地震滑坡危险性真实概率研究,制作了第一代中国地震滑坡危险性概率图。基于9个地震案例开展研究,包括1999年台湾集集、2005年克什米尔、2008年汶川、2010年玉树、2013年芦山、2013岷县、2014鲁甸、2015尼泊尔、2017九寨沟地震,这9次地震中7次发生在中国,2005年克什米尔与2015尼泊尔地震均发生在中国邻区,可以更好的控制模型预测精度。这些地震事件均有详细完整的,利用面要素标识的地震滑坡数据,包括306 435处真实的地震滑坡记录。考虑到真实的地震滑坡发生区域,滑坡面积规模的差别,滑坡与不滑样本的比例等因素,共选取了5 117 000个模型训练样本。选择绝对高程、相对高差、坡度、坡向、斜坡曲率、坡位、地形湿度指数、土地覆盖类型、植被覆盖度、与断层距离、地层、年均降水量、地震动峰值加速度共13个地震滑坡影响因子。采用贝叶斯概率方法与机器学习模型相结合,建立地震滑坡发生的多因素影响模型,得到各个连续因子的权重与分类因子的各个分类的权重。再将模型应用到整个中国研究区,地震动峰值加速度因子为触发因子。分别考虑研究区在经历不同地震动峰值加速度（0.1~1 g,每0.1 g一个结果,共10个结果）下的地震滑坡发生真实概率。此外,还结合中国地震动峰值加速度分布图,得到了中国地震动峰值加速度背景下的地震滑坡发生真实概率分布。     

Landslides induced by the 2017 Mw7.3 Sarpol Zahab earthquake (Iran)

Landslides are the main secondary effects of earthquakes in mountainous areas. The spatial distribution of these landslides is controlled by the local seismic ground motion and the local slope stability. While gravitational instabilities in arid and semi-arid environments are understudied, we document the landslides triggered by the Sarpol Zahab earthquake (November 12, 2017, Mw7.3, Iran/Iraq border), the largest event ever recorded in the semi-arid Zagros Mountains. An original earthquake-induced landslide inventory was derived, encompassing landslides of various sizes and velocities (from rapid disrupted rockfalls to slow-moving coherent landslides). This inventory confirms the low level of triggered landslides in semi-arid environments. It also displays clear differences in the spatial and volumetric distributions of earthquake-induced landslides, having 386 rockfalls of limited size triggered around the epicenter, and 9 giant (areas of ca. 10⁶ m²) active and ancient deep-seated landslides coseismically accelerated at locations up to 180 km from the epicenter. This unusual distant triggering is discussed and interpreted as an interaction between the earthquake source properties and the local geological conditions, emphasizing the key role of seismic ground motion variability at short spatial scales in triggering landslides. Finally, the study documents the kinematics of slow-moving ancient landslides accelerated by earthquakes, and opens up new perspectives for studying landslide triggering over short (~?1–10 years) and long-time (~?1000–10,000 years) periods.

     

5.12汶川8级地震次生地质灾害的基本特征及其形成机制浅析

5.12汶川8级大地震沿龙门山断裂带形成长350多km,宽约50 km的地表破裂带,触发了1万多处崩塌、滑坡、泥石流(碎屑流)地质灾害,其中巨型灾害体87处、大型灾害体606处,形成了136个较大规模的堰塞湖。地震地质灾害的链生特征显著,形成地震-崩塌、地震-滑坡-碎屑流-堰塞湖-堰塞坝溃决-泥石流等典型地质灾害链。地震次生地质灾害具有分布范围广、数量多、种类全、密度大、强度高、致灾重的特点。在部分地区,崩塌、滑坡和碎屑流的分布面积占地震极重灾区面积的30%~58％,甚至高达80％。据初步统计,崩塌、滑坡和碎屑流共导致大约2万人死亡,其中北川县老县城滑坡导致1 600多人死亡。地震次生地质灾害主要沿断裂带、河谷和交通线分布。崩塌、滑坡的破裂源主要位于河流拐弯处靠近侵蚀岸一侧、山脊两侧及坡肩部位,这与上述部位对地震动峰值加速度的放大作用直接相关。地震次生地质灾害主要受地震动峰值加速度和地形控制,其次为岩性、斜坡结构、活动断裂、人类工程活动。许多大型崩塌、滑坡还具有高速远程的特征,部分崩塌、滑坡 碎屑流位移达数km,速度高达100~300 m/s,其运动轨迹复杂多变,常常导致多处人员伤亡,是高山峡谷地区地质灾害风险评估和减灾防灾必须面临的新课题。根据上述情况,文中对汶川地震次生地质灾害的基本特征、分布规律和主要影响因素进行了初步总结,并对地震滑坡的形成机制和运动模式进行了初步探讨。首次提出高山峡谷地区单一斜坡上呈阶梯状多级滑动的群发性地震滑坡的形成模式:强烈地震往往引起剧烈的地面震动,而高陡的山脊及其坡肩部位对地震波具有明显的放大作用,因此,上述部位往往是地震滑坡的高易发地段,当地震动峰值加速度超过不稳定性斜坡的临界峰值加速度时,斜坡失稳破坏形成一系列的群发性滑坡,从上到下往往形成阶梯状多级滑动的滑坡群,此种模式适用于残坡积层、风化层地震滑坡和主滑面较缓的地震基岩滑坡。最后,指出了今后应重点研究的科学问题,并对防灾减灾措施提出了一些建议。     

Landslides and other surface effects induced by the 1997 Umbria–Marche seismic sequence

This paper both describes and discusses landslides and other ground effects induced by the September–October 1997 seismic sequence, which struck the Umbria and Marche regions (Central Italy). Three main events occurred on 26 September at 00:33 and 09:40 GMT, and 14 October with magnitude M_w equal to 5.8, 6.0 and 5.4, respectively; furthermore hundreds of minor but significant events were also recorded. The authors examined an area of some 700 km² around the epicentre (Colfiorito). Primary and secondary effects were observed, including surface faulting phenomena, landslides, ground fractures, compaction and various hydrological phenomena. Surface evidence of faulting reactivation was found along the well-known capable faults, to a total length of ca. 30 km. Landslides, which were the most recurrent among the phenomena induced, consisted mainly of rock falls and subordinately of rotational and translational slides, which were generally mobilised by the inertia forces during the seismic motion. The percentage of reactivated old landslides decreased as the distance from the epicentral zone increased; a similar decrease had been observed for the 1980 Irpinia earthquake (Southern Italy). The ground fracture distribution was consistent with the regional structural setting and the general pattern of macroseismic field. Numerous episodes of hydrological changes were observed within the most severely damaged area. All this evidence confirms the relevance of the study of ground surface effects for achieving a more complete evaluation of seismic hazard.     

A probabilistic evaluation of the size of earthquake induced slope failure for an embankment

The seismic design method for earth structures considers only the safety factor, subsidence and sliding displacement. However, the estimation of the size of slope failures is necessary to judge the remaining function of an embankment after an earthquake event. The size of slope failures due to an earthquake is investigated by considering the heterogeneity of the ground strength and was based on slope stability analysis of two case histories: the 2001 Geiyo Earthquake (Mj6.7) and 2009 Suruga Bay Earthquake (Mj6.5). As a result, we propose a method for slope failure size estimation based on the maximum slip surface. The proposed method enables a rational assessment of the functional loss of an embankment in terms of the slope failure size.