黄土河谷场地地形放大效应的研究

使用黄土河谷场地模型对地震动峰值加速度和频谱特征进行研究。结果表明，不同工况下各观测点PGA的放大比呈现出不同的变化规律。分析山顶和山谷各点的傅里叶谱以及谱比发现，在地形和土层共同作用下的放大效应是各自单独作用下放大效应的乘积。     

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Seismic response of cracking features in Jubao Mountain during the aftershocks of Jiuzhaigou Ms7.0 earthquake

Jiuzhaigou is a world-heritage site located in the plateau area of Northwest Sichuan Province,China. Serious slope failures in the epicentral area were triggered by the Ms7.0 Jiuzhaigou earthquake occurred on August 8, 2017. The source areas of the hazards are usually concentrated near ridge crests,revealing the possible occurrence of ground motion amplification phenomena. To explore the role of the amplification of ground motions in the formation of earthquake-triggered slope failures, two seismometers were installed, on the next day after the main shock, at the bottom of the slope of Jubao Mountain near the seismogenic fault. The two monitoring sites are located at elevations of 1414 m(J1) and 1551 m(J2, the top of the mountain). Five aftershocks were recorded by the monitoringinstruments. We compared the mean levels of the peak ground acceleration(PGA) observed at different locations, and investigated the directional variations in the shaking energy by analyzing the polar diagrams of the Arias intensity(Ia). Then, in order to identify the directional resonance phenomenon and their frequencies and amplification coefficients, we examined the horizontal-to-vertical spectral ratio(HVSR) and the standard spectral ratio(SSR). Polar diagrams of the Arias intensity(Ia) indicated that the site response of Jubao Mountain showed a pronounced directivity(in the EW direction) with shaking maxima near the hill top oriented orthogonally to the elongation of the relief. We observed an obvious resonance phenomenon at site J2 at relatively low frequencies(2.5-9 Hz) and very weak spectral amplifications at site J1 at high frequencies(5-15 Hz), which suggested that the predominant frequency of monitoring site J2 was obviously attenuated and that the difference in the spectra was related to the influences of the local-scalesite conditions of the whole mountain. The results of spectral ratio analyses(HVSR and SSR) showed that the direction of resonance was concentrated around an EW orientation, and the amplification factors near the hill top were larger than 2. It suggests that geologic factors also play a significant role in the anisotropic amplifications affecting the tops of slopes besides the topographic effects.     

强震山区低山斜坡地震动响应特征分析

2019-06-17四川省宜宾市长宁县6.0级地震后,双河镇布设了多个地震监测仪器,以获取不同场地条件下的地震动相关参数.研究结果表明:1)在同一介质下,60 m高程对地震动的峰值加速度放大可达1～3倍,阿里亚斯强度放大可达2～5倍,同时微地貌的不同可使放大效应具有一定的方向优势;2)在同一高程不同介质条件下,相较于砂...     

Slope seismic response monitoring on the aftershocks of the Wenchuan earthquake in the Mianzhu section

Previous investigations have shown that the seismic response of slopes during the Wenchuan earthquake was highly variable.The present study tries to give an answer to the question:Which are the main factors affecting the seismic response degree of slopes? With the support of the China Geological Survey Bureau,we set 3 monitoring sections in Jiulong slope,Mianzhu city,China with the aim to record the site response of the slope during the aftershocks of the Wenchuan earthquake.After the Wenchuan earthquake,which happened on 12 May 2008,30 aftershocks have been recorded in these monitoring points.We analyzed 11 records,with magnitudes ranging from ML = 4.6 to ML = 3.1.The amplification factors of the horizontal compound PGA and 3D compound PGA have been determined for the 3 points at different elevations on the slope.Results showed that the dynamic response of the slope on the earthquake was controlled by factors such as topography and the thickness of the Quaternary overburden.     

基于强震记录的唐山5.1级地震强地面运动特征及局部场地效应分析

利用京津冀地区214个强震台捕获的2020-07-12唐山市古冶区5.1级地震加速度波形记录,统计分析记录数量随震中距变化的特征,绘制峰值加速度等值线图。将近场6个土层台记录的线弹性反应谱与我国抗震设防反应谱进行比较,采用传统谱比法分析近场局部土层对地震动的放大作用。将观测的谱加速度与国内常用的几种地震动预测模型进行对比,计算其归一化残差,研究中、远场局部场地条件对地震动幅度和主要作用周期的影响,给出各周期谱加速度的空间展布,并结合场地环境分析中场地震动被显著放大的原因。     

四川珙县下软上硬山岭地貌斜坡地震动响应特征

强震中下软上硬坡体同震崩塌发育, 为了揭示这类坡体地震动的响应特征, 在珙县五同村安置了强震监测仪, 对斜坡表面和不同岩性的地震动响应进行监测, 并记录到不同方位、不同震中距的2次地震。研究表明: ①地震动响应规律有极强的方向性和距离性。2次地震相距监测站台的方向和距离不同, 使Ms 4.0级地震的峰值加速度和阿里亚斯强度反而比Ms 3.2级地震小。②0~30 Hz的地震波在低地山岭的高陡临空面附近有放大效应。1#监测点的主频小于3#与5#监测点, 3#监测点的主频最高。5#点的幅值范围为0.018~0.055 m/s-2, 3#点幅值范围为0.036~0.087 m/s-2, 3#点相较于5#点, 其三向最高幅值同比放大了1.58~2.0倍。③泥质砂岩的主频为4.8~8.4 Hz, 灰岩的主频为5.5~21.4 Hz, 不同的岩层共振频率不同, 灰岩对地震波的选频放大效应强于泥质砂岩。④地震波在不同高程的山岭斜坡部位具有选择放大作用, 在一定范围内高程越大地形放大效应越明显。      

青海门源6.4级地震兰新高铁沿线强震数据分析

基于2016-01-21青海门源6.4级地震,通过分析高铁沿线台站强震数据的峰值加速度、峰值速度和仪器烈度值表明,将实时仪器烈度值作为高铁地震监控系统的报警参数受场地条件影响较小。利用沿线台站近高铁和远高铁监测点的谱比值来解释局部复杂场地条件对峰值加速度的影响,通过比较台站计算与设计的反应谱来预测高铁地震台站附近的桥梁震害情况。     

GIS-based evaluation on the fault motion-induced coseismic landslides

Earthquake-induced potential landslides are commonly estimated using landslide susceptibility maps. Nevertheless, the fault location is not identified and the ground motion caused by it is unavailable in the map. Thus, potential coseismic landslides for a specific fault motion-induced earthquake could not be predicted using the map. It is meaningful to incorporate the fault location and ground motion characteristics into the landslide predication model. A new method for a specific fault motion-induced coseismic landslide prediction model using GIS (Geographic Information System) is proposed herein. Location of mountain ridges, slope gradients over 45 o , PVGA (Peak Vertical Ground Accelerations) exceeded 0.15 g, and PHGA (Peak Horizontal Ground Accelerations) exceeded 0.25 g of slope units were representing locations that initiated landslides during the 1999 Chi-Chi earthquake in Taiwan. These coseismic landslide characteristics were used to identify areas where landslides occurred during Meishan fault motion-induced strong ground motions in Chiayi County in Taiwan. The strong ground motion (over 8 Gal in the database, 1 Gal = 0.01 m/s 2 , and 1 g = 981 Gal) characteristics were evaluated by the fault length, site distance to the fault, and topography, and their attenuation relations are presented in GIS. The results of the analysis show that coseismic landslide areas could be identified promptly using GIS. The earthquake intensity and focus depth have visible effects on ground motion. The shallower the focus depth, the larger the magnitude increase of the landslides. The GIS-based landslide predication method is valuable combining the geomorphic characteristics and ground motion attenuation relationships for a potential region landslide hazard assessment and in disaster mitigation planning.     

基于GeoKSCloud的地震影响场分析云服务研究——以福建省为例

地震发生后处于不同地震烈度区域的地物受灾程度不同。快速准确地获取地震影响或波及范围内地震烈度空间分布,是震后应急救援的重要依据和主要参数。依托云计算技术,以云服务方式构建地震烈度速报系统,提供可扩展、可配置、开放透明的地震影响场分析应用服务,将是我国烈度速报系统研究开发与应用中的一项新技术和发展趋势。本文依托研究小组自主研发的地理知识云服务系统GeoKSCloud,以福建省为研究区域,在提出适用于福建省地震烈度衰减关系与地震动峰值加速度场地校正方法的基础上,开展了地震影响场分析云服务系统的设计与实现工作,分析了地震影响场分析云服务的运行机制和服务组合工作流;实现了地震烈度衰减关系计算方法、场地放大因子校正方法、网格点场地类别属性获取、网格点沿地震衰减长短轴方向的坐标变换等相关原子服务的云服务封装,以及支撑数据云存储、网络地理信息系统的云服务门户的开发与集成;最后,以1604年发生在泉州近海7.5级大地震为震例,在云服务门户进行了全省范围内所有等间距网格点地震峰值加速度(基岩PGA和地表PGA)的计算、插值,并进行计算结果与实际调查数据的对比分析。结果表明,因充分考虑了具体场地的放大效应,构建的地震影响场分析云服务,不仅较传统单凭地震烈度衰减关系确定地震动峰值加速度方法更加精细化,而且提供的服务与传统的网络服务相比具有可扩展、可配置、开放透明等明显优势,可为我国烈度速报系统研究与应用提供一个共性技术与支撑服务平台,创新地震烈度速报的运营模式。     

工程场地地震动参数的确定

以咸阳某工程场地为例，首先阐述了场地的地震地质条件，然后在场地地震危险性概率分析的基础上，对场地土层进行一维地震反应分析计算，确定了该工程场地地震动参数，为抗震设计提供了依据。     

Seismic response of the Lengzhuguan slope during Kangding Ms5.8 earthquake

In order to investigate the role of the amplification of peak ground acceleration(PGA) in seismic landslide formation mechanisms and study how earthquake waves interact with rock structures, a few strong-motion seismometers are installed at various locations on both sides of the Lengzhuguan gully. Five strong-motion seismometers were triggered at different depths in a tunnel at the same altitude during the Kangding Ms 5.8 earthquake on November 25 th, 2014. The data reveal that the horizontal peak acceleration(PGA_H) at each site decreased with increasing site depths. The PGAH at the deepest monitoring site(99 m from the tunnel entrance) was approximately half that of the outermost site. The amplitude of the acceleration response spectrum was also attenuated from the entrance inwards, the dynamic magnification factor(β) of the standard acceleration spectrum was less than 3.5, and rate of change was the same as that for the amplitude acceleration response. The Fourier spectra of each monitoring site also decreased from the outside inwards, and the components of the Fourier spectra were more complex at the surface.     

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Assessment of seismic ground motion amplification and liquefaction at a volcanic area characterized by residual soils

A seismic hazard was assessed related to site effects at Abbadia San Salvatore, central Italy, on the Mt. Amiata slopes, an ancient volcanic area characterized by residual soils(thick layers of loose to dense sands originated from weathering of the trachydacitic lavas). The seismic ground amplification and soil liquefaction related to these layers were recognized as the major seismic hazards for the area.Geological, geophysical, and geotechnical surveys were carried out on the volcanic rocks. The Horizontal-to-Vertical Spectral Ratio(HVSR) analysis of 252 noise measurements and 29 shear-wave velocity models of the subsoil allowed a seismic microzonation of the studied area, distinguished by thick weathered volcanic sands and shear-wave impedance contrast with respect to the seismic bedrock(volcanic bedrock). The differentiation of classified zones allowed recognition of areas characterized by residual(almost undisturbed) soils from those with soils probably affected by flowing water. The analysis of hazards revealed that peak acceleration by seismic amplification of ground motion exceeded the value set by the national rules(0.175 g) in a restricted area of the zone characterized by the most perturbed soils(Zone D); the potential occurrence of soil liquefaction was also greater in this zone. Finally, the study showed potential high hazards due to site effects of the volcanic mountainous area characterized by residual soils as opposed to an alluvial plain formed by volcanic debris where these effects have generally been more recognized.     

Analysis of the stability and seismic behavior of the geosynthetic-reinforced embankments under earthquake

The stability and seismic behavior of geosynthetic-reinforced embankments during the earthquake is not well known.In this paper,the damage types of embankments were summarized,and the seismic stability of reinforced embankment were analyzed through an earthquake damage investigation in the Wenchuan earthquake region.Then,large-scale shaking table model tests were performed on the geosynthetic-reinforced embankment.The results show that the damage level of the reinforced embankment was almost less than that of the unreinforced embankment.The peak seismic earth pressure was nonlinear along the height of the embankment,the largest peak seismic earth pressure was roughly in the middle of the embankment slope.The peak ground accelerations(PGA)amplification factor first showed an increasing pattern and then a decreasing pattern with the increase of elevation,but there was a final increasing trend along the height of the reinforced embankment.The results can help to establish the proper design of the reinforcement embankments under earthquake conditions.     

地脉动频谱特性在探究场地评价中的应用

运用单点谱比法对地脉动频谱特性进行分析,根据频谱类型分类结果给出场地卓越周期建议值。在已有钻孔资料基础上,建立卓越周期与覆盖层厚度间的相关关系,并通过实际的工程数据验证了二者关系式的准确性和普适性。由于地脉动观测具有经济、简单、快捷的优点,可将其运用到不宜进行钻孔勘探的复杂场地,从而为该地区工程场地地震安全评价和地震小区划、场地类别划分、场地选择和评价提供基础资料。     

中国东西部地区震后形变有效松弛时间研究

顾及脆性转换带上的断层蠕动及其深部黏滞流对震后地表位移的影响,对5次大地震的震后垂直位移进行了最小二乘反演,并估计了有效松弛时间。反演结果表明,中国东、西部地震的有效松弛时间差异很大,其中唐山地震的有效松弛时间最长(10.3年),邢台地震次之(4.4年),而西部通海、炉霍、共和等3次地震的有效松弛时间则仅为2年多。究其原因,可能主要是由于中国东部和西部地区上地壳厚度不同以及下地壳、上地幔黏滞系数的差异所致。     

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Calculation of landslide occurrence probability in Taiwan region under different ground motion conditions

In this study, Bayesian probability method and machine learning model are used to study the real occurrence probability of earthquake-induced landslide risk in Taiwan region. The analyses were based on the 1999 Taiwan Chi-Chi Earthquake, the largest earthquake in the history in this Region in a hundred years, thus can provide better control on the prediction accuracy of the model. This seismic event has detailed and complete seismic landslide inventories identified by polygons, including 9272 seismic landslide records. Taking into account the real earthquake landslide occurrence area, the difference in landslide area and the non-sliding/sliding sample ratios and other factors, a total of 13,656,000 model training samples were selected. We also considered other seismic landslide influencing factors, including elevation, slope, aspect, topographic wetness index, lithology, distance to fault, peak ground acceleration and rainfall. Bayesian probability method and machine learning model were combined to establish the multi-factor influence of earthquake landslide occurrence model. The model is then applied to the whole Taiwan region using different ground motion peak accelerations(from 0.1 g to 1.0 g with 0.1 g intervals) as a triggering factor to complete the real probability of earthquake landslide map in Taiwan under different peak ground accelerations, and the functional relationship between different Peak Ground Acceleration and their predicted area is obtained.