珙县低山区不同震源作用下斜坡地震动响应

在宜宾市珙县五同村布设斜坡地震动监测仪器,采集兴文县3.1级、珙县4.5级及长宁县4.6级地震数据。对监测剖面上1^#、2^#监测点采集到的珙县余震地震动响应数据进行滤波和校正处理,对比分析震级、高程、方位等因素对斜坡造成的地震响应后认为：1）当地震波的半波长与山体某些特定部位之间的距离接近时,斜坡地形与地震波的波峰产生耦合作用,地形放大效应显著,达到参考点的2.765倍,此处山体更容易产生较大幅度的摇晃,造成山体地质灾害;2）分析珙县4.5级与长宁县4.6级地震得出,当地震波沿特殊部位（如山脊等）传播时,地震加速度及阿里亚斯强度更加显著;3）分析地震加速度变化得出,在地震荷载作用下,随着震级的增大,斜坡的加速度响应也会增大;4）随着高程和震级的变化,监测点的地震加速度和阿里亚斯强度随之变化,高程和震级对斜坡的地震动响应具有放大效应;5）在高程和微地貌的耦合作用下,斜坡地震加速度也具有明显的放大效应。     

四川珙县M_s 5.4级地震斜坡地震动响应特征

四川珙县M_s 5.4级地震是长宁M_s 6.0级地震第三大余震,在震中区诱发了多处滑坡和崩塌,研究坡体不同部位地震动响应特征对地震地质灾害预测和防治意义重大。通过在距离震源近的斜坡不同位置布置监测点,获取地震动参数及相关变化规律,对研究区域的坡体进行稳定性分析和研究。结果表明:地震在南北向的放大效应大于东西向,覆盖层土体最大位移达到了7.42 mm,与地震时南北向晃动强烈吻合;对比分析各个监测点的峰值加速度(PGA)、阿里亚斯(Arias)强度,覆盖层土体比高位基岩的放大效应显著;基岩地震波以低频为主,卓越频率为2～5 Hz,随着高程的增加对高频的地震波有过滤作用,在山顶3~#监测点的阿里亚斯强度比山脚1~#监测点(参考点)放大数倍,地震动能量强;通过该区域的抗震设计反应谱与监测反应谱对比分析,可以得出覆盖层土体和高位基岩地震动强烈,前者的宏观表现为覆盖层土体上老旧房屋毁坏严重,后者为高位基岩坡体滑坡和崩塌。     

强震作用下斜坡表面放大效应的三维离散元模拟

为研究强震作用下斜坡表面的动力放大效应, 以陕西勉县某岩质斜坡为例, 建立了三维模型。运用离散元软件3DEC, 模拟了动力条件下斜坡的变形失稳过程, 分析了斜坡表面的动力响应特征, 研究了不同地震波输入工况条件下坡体表面动力响应差异。研究结果表明: 考虑地震纵波的影响时, 竖向加速度得到显著增强, 坡面的PGA放大系数增强了约1.62倍; 坡面形态强烈影响着斜坡表面的动力响应特征, 强震作用下, 斜坡坡肩及坡形转折处的放大效应均十分强烈, 凸出部位次之, 坡表两侧的放大效应最弱; 不同输入工况下, 斜坡坡形转折处的水平向PGA放大系数均维持较高值, 特别是在仅输入水平向加速度的条件下, 该部位在地震滑坡灾害预防中应特别注意; 强震作用下滑坡的运动过程可概括为滑坡孕育启动阶段—挤压碰撞高速运动阶段—堆积阶段。研究成果可为该地区防灾减灾工作提供一定理论支持。      

兴文MS5.1地震震裂斜坡地震动响应特征

通过对宜宾珙县震裂斜坡上的3台地震动监测仪器记录到的2022-04-06宜宾兴文M_S5.1地震地震波传播数据进行滤波和基线校正,分析时程曲线、傅里叶频谱和加速度反应谱。结果表明：1)本次地震持时短、幅度小,2^#和3^#监测点S波持时较1^#监测点长2～5 s; 2)傅里叶频谱显示,水平方向低频衰减、中高频放大、频带变宽,垂直方向变化不明显;3)以1^#监测点为参考,2^#和3^#监测点峰值加速度(PGA)放大系数为1.17～3.05,阿里亚斯强度(AI)放大系数在EW和UD向为4.43～7.59,3^#监测点NS向可达18.86;4)对比分析芦山仁家村(非震裂斜坡)监测剖面,认为珙县震裂斜坡存在放大效应。     

丘陵地貌区斜坡强震动响应特征——以四川省长宁县为例

前人对高山峡谷地貌区高位斜坡动响应研究较多,但对低山、丘陵地貌区斜坡强震动响应研究很少。并且,研究这类地区顺倾斜坡的地震动响应对揭示长宁M_s 6.0级地震丰富的次生山地灾害动力机理具有一定意义。在四川省长宁县丘陵地貌区典型顺倾斜坡不同部位安置强震监测仪器,捕捉到40多次余震,通过SeismoSignal软件处理典型余震数据,分析峰值加速度、阿里亚斯强度、傅里叶频谱、加速度反应谱,进而采用水平/竖直向谱比法分析局部场地效应,最后对比分析低山、丘陵地貌区与高山峡谷地貌区的斜坡动响应。结果表明:坡顶峰值加速度可达4.171 m·s~(-2),最大位移可达0.008 05 m,当峰值加速度大于1.0 m·s~(-2)时,阿里亚斯强度出现陡增的趋势;局部地形的放大效应使得地质灾害以沿山脊的裂缝及小型崩塌为主,在低频2～5 Hz处,斜坡中上部易发生山体共振。以上研究揭示了砂、页岩顺倾斜坡高位放大效应,为地震山地灾害易发性区划提供地震监测资料。     

台湾集集地震近断层地震动工程特性与时频特征分析

为研究近断层不同区域地震动工程特性与时频特征,考虑近断层地震动方向性效应、滑冲效应、上盘效应等特性与断层类型的关系,基于PEER强震数据库,选取台湾集集（Chi-Chi）地震作为研究对象,依据断层破裂带与地震动观测台站的相对位置关系,将其近断层地震动划分为破裂前方区域（RFR）、断层上盘区域（HWR）、断层下盘区域（FWR）及破裂后方区域(RBR)4类,对比分析近断层不同空间地震动的三要素特性,并利用希尔伯特-黄变换（HHT）进一步分析其能量在时频分布上的差异。结果表明：1）近断层不同区域地震动PGA、PGV、PGD及PGV/PGA具有显著差异,给结构地震响应带来极大影响;2）RFR区域地震动呈显著的长周期效应,RBR区域地震动具有高频大幅值特点,HWR区域和FWR区域地震动同时具有高频大幅值特点和显著长周期效应;3）在时频域内,RFR、HWR、FWR、RBR区域地震动能量高值都主要集中在0~5.2 Hz的中低频段,其中HWR区域的地震动最大瞬时能量最大,RFR区域的地震动最大瞬时能量最小。     

四川芦山M_s 7.0级地震的地质环境影响分析

2013年4月20日四川省雅安市芦山县发生Ms7.0级地震,此次地震对地质环境的影响备受各界关注。基于遥感解译与震后现场调查,对芦山地震的地质环境影响进行了初步分析。结果发现芦山地震的地质环境影响主要有:诱发较为广泛的崩塌等次生山地灾害,崩塌以小型为主,主要分布在双石—大川断裂带槽谷以及北西向几个深切峡谷段,如S210省道芦山—宝兴峡谷、芦山—双石峡谷、龙门—太平峡谷,其中震中区宝盛、太平镇崩塌密度最大;泥石流动静物源有不同程度增加,崩塌新增了泥石流沟的物源;斜坡上缓坡带也堆积有新的崩塌物源,使震后沟谷泥石流与坡面泥石流发生的概率增加;斜坡震裂现象较普遍,震动引起斜坡表层覆盖层不均匀沉降,宏观上表现为地面开裂、房屋开裂以及公路路基失效等;沙土液化加重灾害程度,震动引起发震断裂槽谷区砂土液化,使发震断裂带上地基失效,震害加重;厚覆盖层场地效应使地震下盘平坝区震害异常,下盘前陆盆地厚覆盖层地区地震波放大效应使芦山县龙门、清仁以及天全县老场、仁义平坝区及斜坡地带震害严重;芦山地震地质环境影响最大的区域是震中区太平—宝盛一带,其次是断裂带下盘5km—上盘5km的地带、宝兴县城区域及前陆盆地带。     

“6.1”芦山地震作用下宝兴新华村滑坡动力响应与失稳过程离散元模拟

斜坡浅表层是各类地震地质灾害发育的潜在破坏位置,坡面形态和坡体结构往往造成斜坡动力响应及破坏的复杂化。为探究不稳定斜坡浅表潜在滑动层动力响应特征与失稳过程,以芦山M_s6.1级地震触发的新华村滑坡为例,基于现场调查采用离散元方法建立了二维计算模型,分析了该斜坡潜在滑动层及坡面形态的动力响应特征并对其失稳过程进行了模拟。结果表明：(1)斜坡浅表潜在滑动层具有强烈动力放大效应;(2)微地貌对于潜在不稳定斜坡坡面的放大效应具有明显的影响,浅表潜在滑动层水平向及竖直向加速度在凸出部位的放大效应显著,凹陷部位相较于凸出部位放大效应较低;(3)研究揭示新华村滑坡在微地貌的作用下凸起地形呈现先于凹陷地形遭受破坏,其失稳过程分为震动放大局部震裂-凸出地形破坏-凹陷地形破坏-完全破坏整体下滑-重力堆积5个阶段。该研究结果有助于提升防灾人员对地震诱发潜在不稳定斜坡失稳的认识,为防灾减灾提供理论和数据支撑。     

浑厚山体随高程增加由表及里地震动响应研究

为探究浑厚山体不同高程由表及里地震动响应规律,以冷竹关山体为例,采用离散元软件建立地形与风化介质组合模型,并从底部边界输入汶川地震波信号,研究该山体两侧边坡的内外动力响应规律。结果表明,随着高程的增加,靠大渡河一侧边坡坡体内与坡表的加速度放大系数均表现出先增大后减小的节律性变化,在近坡顶时增大较快并达到最大值;靠近瓦斯沟一侧边坡坡表受地形起伏的影响,加速度放大系数存在凸坡放大、凹坡减小的特征;相同高程,随边坡由表及里深度的增加,加速度放大系数表现为逐步减小,当距坡表150~200 m时放大曲线趋于平缓;随高程的增加,加速度放大系数由表及里的减小速度变缓,且放大曲线收敛平缓的深度增大;随岩体风化程度的增加,岩体介质波速降低,共振效应使得加速度响应增大,与此同时,斜坡地形与介质组合效应使得坡表峰值加速度放大系数在2.0附近。     

2019-12-26湖北应城M4.9地震强震动特征分析

对2019-12-26湖北应城M4.9地震的强震加速度记录进行基线校正和滤波处理,分析地震动场的分布特征。结果表明,此次地震记录的峰值加速度（PGA）随距离衰减较快;场地效应、上盘效应和破裂方向性效应共同导致地震动产生巨大差异。对应城地震台的强震记录进行旋转,其顺断层方向记录与垂直断层向和垂直向记录差异明显,存在一段周期约为0.3 s的类简谐强震动,与以走滑为主的震源机制相吻合。     

用随机有限断层方法模拟2016-11-13新西兰Mw7.8地震

在未来大地震发震构造已知的前提下，提出用经验公式确定大地震断层长度、宽度、地震矩和滑动分布等参数，并用随机有限断层方法预测未来大地震。用随机有限断层方法模拟2016-11-13新西兰M_W7.8地震的12个基岩台站地震动时程和反应谱，并用模拟的频谱幅值与记录频谱幅值平均比值确定模拟误差。结果表明，在周期为0~10 s的范围内，模拟误差在0.92~1.08之间，不同频率模拟误差的标准差变化范围不超过1。95%的置信区间宽度随频率无明显变化，模拟结果反映了地震动记录的平均效果。用准随机方法重新获取新西兰大地震断层初始破裂点和位错滑动分布，模拟地震动并计算模拟误差随频率的变化，得到与最初模型相似的结论，从而进一步证实了本文提出的获取震源参数并用随机有限断层方法预测未来大地震的可靠性，且其特别适用于大地震远场模拟。     

Rockfall seismic features analysis based on in situ tests:frequency,amplitude, and duration

In the seismic event classification,determining the seismic features of rockfall is significantly important for the automatic classification of seismic events because of the huge amount of raw data recorded by seismic stations in continuous monitoring. At the same time, the rockfall seismic features are still not completely understood.This study concentrates on the rockfall frequency content, amplitude(ground velocity), seismic waveform and duration analysis, of an artificial rockfall test at Torgiovannetto(a former quarry in Central Italy). A total of 90 blocks were released in the test, and their seismic signals and moving trajectories were recorded by four tri-axial seismic stations and four cameras, respectively. In the analysis processing,all the artificial rockfall signal traces were cut separately and the seismic features were extracted individually and automatically. In this study, the relationships between a) frequency content and impacted materials, b) frequency content and the distance between block releasing position and seismic station(source-receiver distance) were discussed. As a result, we found that the frequency content of rockfall focuses on 10-60 Hz and 80-90 Hz within a source-receiver distance of 200 m, and it is well correlated with impacted material and source-receiver distance. To evaluate the difference between earthquake and rockfall, 23 clear earthquake signals recorded in a seven month-long continuous seismic monitoring, carried out with the four seismic stations, were picked out, according to the Italian national earthquakes database(INGV). On these traces we performed the same analysis as in the artificial rockfall traces, and two parameters were defined to separate rockfall events from earthquake noise. The first one, the amplitude ratio, is related to the amplitude variation of rockfall between two stations and is greater than that of earthquakes, because of the higher attenuation occurring for rockfall events, which consists in high frequencies whereas for earthquakes it consists in low frequencies. The other parameter, the shape of waveform of signal trace, showed a significant difference between rockfall and earthquake and that could be a complementary feature to discriminate between both. This analysis of artificial rockfall is a first step helpful to understand the seismic characteristics of rockfall, and useful for rockfall seismic events classification in seismic monitoring of slope.     

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泥质砂岩残积土边坡降雨冲刷特性

泥质砂岩残积土作为一种结构性很强的特殊土, 具有崩解性强、抗冲蚀性差以及扰动性极大的特点, 对工程建设有较大影响。为了探究泥质砂岩残积土边坡降雨冲刷机理, 设计了边坡降雨冲刷试验, 通过现场三维激光扫描技术测试分析了其表面冲刷效应; 利用高密度电法进一步明确了泥质砂岩残积土边坡的入渗特性、表面冲刷演化机制及冲刷破坏机理。结果表明: 冲刷试验的最初阶段, 降水入渗强且主要向坡脚处运移, 坡表未形成明显的细沟; 冲刷试验中期, 坡脚处土体最先达到饱和而形成坡面径流, 细沟贯通扩大形成小规模冲槽以及片蚀区; 冲刷试验后期, 坡面中部和坡脚处土体冲蚀严重, 坡脚处的冲槽向上部延伸, 片蚀区扩大, 导致表层土体结构发生变化, 渗透性差异明显; 泥质砂岩残积土坡体降雨冲刷主要划分为表层溅蚀、下层潜蚀和细沟贯通3个阶段, 坡面土体流失主要发生在最后一个阶段, 细沟率达到最高值16.9%, 细沟贯通率也高达0.74。研究结果可以为深入探讨泥质砂岩残积土边坡冲蚀防护和研究冲蚀防护机理提供基础资料。      

利用张衡一号卫星电场数据研究吉林松原、河北唐山MS5.1地震前后空间电场时空演化特征

利用我国第一颗电磁监测试验卫星张衡一号电场探测仪（EFD）载荷记录到的ULF/ELF频段电场功率谱密度（PSD）数据,限制Dst≥－30 nT和K_p＜3排除空间磁环境扰动后,分4个频段对2020年唐山古冶M_S5.1地震和2019年吉林松原M_S5.1地震前后空间电场时空演化特征进行研究。结果发现,2020年唐山古冶M_S5.1地震4个频段扰动幅度均显示出震前先抬升至最高点超过2倍均方差,而后在下降过程中发震,震后恢复的规律,且第2频段异常尤为明显;4个频段扰动幅度时间序列特征相似,且震前均超过2倍均方差。2019年吉林松原M_S5.1地震不同频段的扰动幅度时间序列特征不同,仅有第2频段超过2倍均方差。2次地震均在第2频段（371~879 Hz）出现震前异常扰动,认为该频段是地震异常提取的优势频段。     

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.     

三峡水库蓄水后小微震事件的震源机制及成因分析

利用三峡工程地震监测台网记录的2003~2014年地震振幅比和P波初动数据,对三峡水库重点监视区蓄水后地震的震源机制进行解析。结果表明,这些地震震源的基本特征是大仰角的主压应力轴和近于正断的震源错动。在库水的循环加卸载及其水岩的理化作用下,浅表岩层软弱结构面（体）失稳,是蓄水后小微地震活动的主要诱因。 值得注意的是,2010年以后,逆冲走滑类型地震的比例显著增多,显示了区域构造应力场的控制作用。     

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.     

2006年9月秭归泄滩极微震群初步研究

2006年 9月17～22日在秭归泄滩镇西侧发生了一次极微震群活动,其中最大地震为9月20日21时10分 ML1.8级.分析结果表明:本次震群的震中主要集中于泄滩镇老石门村至老泄滩一线,震源深度为海平面以上0.5 km范围内,为正倾滑机制解;该震群频谱最佳频率主要集中在2 Hz左右,初步推断该震群为地表层重力作用下矿塌型地震并伴有几次浅层微滑坡.