渭河盆地活动构造与地震

渭河盆地发育着几个活动断裂系统。近东西向弧形断裂系由七条近东西向的弧形断裂组成,它们纵贯全区,控制了渭河盆地的基本轮廓,构成了渭河地堑构造的主体,决定了盆地的形成和发展,导致盆地内6级以上强震沿其分布。东西向和北西西向两断裂带是盆地内的重要成员,前者可能表现为蠕动横移,后者控制渭河水系流向,可能是2次强震的发震构造。北北东向断裂系积极改造水系控制现今中小地震译动;北西向弧形断裂系决定了盆地西端的地震活动。南北向破裂形迹微弱似乎不足以发震。     

横断层作用下汶川地震与芦山地震发震机制新探

在分析龙门山断裂带区域构造背景、青藏高原东缘新构造运动特征的基础上,阐述龙门山断裂带的构造格局,并利用横断层对龙门山断裂带进行分段;同时,对汶川地震与芦山地震的发震机制及其相互关系进行探讨,并对未来强震危险区进行预测。结果表明:汶川地震具有深部构造的控震作用,其深部孕震机制十分复杂,而芦山地震没有明显的地表破裂带,为一次盲逆断层型地震;卧龙—怀远一线为地壳物质运动方向和主断裂走滑方向发生反向的转换带,发生在其两侧的地震是各自独立的,即汶川地震与芦山地震相互独立;汶川地震与芦山地震发震时,龙门山断裂带中未活动的区域存在较高的地震危险性,尤其是卧龙—怀远和小金横断层之间的断块为强震危险区,虎牙断裂与主断裂交汇处也是强震较危险区。     

两次门源MS6.4地震前垂直形变的对比分析

利用甘肃民乐至青海门源的多期跨断裂水准资料,对比分析了1986年、2016年两次门源6.4级地震前的垂直形变。结果表明：1)两次地震前的孕震背景不同。1986年门源地震前祁连山相对民乐盆地大幅上升,区域压应力呈增强状态;2016年门源地震前祁连山相对民乐盆地上升不明显,区域压应力相对松弛。2) 两次地震前垂直形变表现形式不同。1986年门源地震前冷龙岭断裂附近出现加速上升,2016年门源地震前冷龙岭断裂附近出现上升和下降相间的不稳定变化。3)两次门源地震前在发震断裂附近都观测到地表隆起区,与地震孕育的膨胀模式相吻合。     

地震形变的断层分层、分段活动模式

采用横向分段、纵向分层的断层位错模式研究了美国加州帝国河谷地区四期三角复测资料,确定了1940年该河谷地区的M_ W=7.1级地震的断层活动方式及震后不同时期的滑动速率。 模式的要点是:大震间歇期发震层(孕震层)是闭锁或接近于闭锁状态,地表浅层和地壳深层可以发生无震滑动(蠕动);地震发生时,浅层与发震层产生滑动,且滑动量沿断层呈非均匀分布。     

2016年青海门源MS6.4地震前的区域地壳形变特征

选取2016-01-21青海门源MS6.4强震发震区域周围200 km范围的10个连续GPS观测站和74个流动GPS观测站资料,分析研究2016年门源MS6.4地震之前的区域地壳形变特征：1）基于10余年GPS资料的速度场计算结果表明,发震区域所处的祁连-海原断裂系具有显著高于周边区域的地壳应变率和地震矩累积率。在发震区域20 km × 20 km范围内,最大和最小主应变率分别为21.5 nanostrain/a（方向NW-SE,拉张）和-46.6 nanostrain/a (方向NE-SW,挤压),地震矩累积率达17.4×1015 N·m/a。主应变挤压的主轴方向与本次地震的震源机制相一致。2）基于震前6 a连续GPS观测站坐标变化时间序列的计算结果表明,自2010年以来,发震区域的面膨胀值随时间呈“非线性”不断变小的趋势,反映出发震区域一直处于应变的挤压缩减状态,但在震前的2~3个月,面膨胀与最大剪切应变均发生了一次明显的反向趋势变化。这些震前的地壳形变异常变化,或许反映了发震区应力-应变积累在接近临界破裂状态时的非线性调整。     

2010年玉树地震库仑应力变化对2016年杂多地震的影响及区域危险性评估

在以往研究的基础上，利用弹性位错理论和岩石圈分层粘弹性模型，进一步分析2010年玉树地震同震及震后应力变化对2016年杂多地震的影响，讨论玉树地震和杂多地震对研究区主要活动断裂的应力影响及未来地震危险性。结果表明，玉树地震同震库仑应力使杂多地震震中位置应力升高1.476 kPa。2010年玉树地震至2016年杂多地震的6 a内，震后粘弹性松弛作用使研究区域库仑应力增强区域应力持续集中，并使应力影区进一步释放应力，杂多地震位于玉树地震导致的库仑应力增强区域。2016年杂多地震发生时，其震中位置应力升高3.902 kPa。采用多组不同模型参数的研究结果均显示，玉树地震对杂多地震孕育起促进作用。2016年杂多地震同震破裂仅影响震中周边小范围区域的应力状态，在杂多断裂带西北端出现应力高值区域。2010年玉树地震同震及震后作用使甘孜-玉树断裂的叶诺卡-结隆段、巴塘乡-洛须段、当江段、巴塘乡断裂中段及五道梁-曲麻莱断裂称多段应力明显升高。甘孜-玉树断裂西北段的叶诺卡-结隆段、巴塘乡-相古段地震空区的地震危险性较高。     

利用区域水准测量资料判定地震危险区

利用中国西部地区２０多年的水准测量资料，用富氏分析法分离地壳垂直形变信息，进而计算了测区的垂直形变场分数维，并分析了它在孕震过程中的变化特征。结果表明，区域垂直形变场分数维在地震前下降，同震时段降至最低。在此基础上，提出了划分地震危险区的判据，并结合实例介绍了计算方法和步骤     

基于GNSS应变时序的云南地区构造运动与地震事件孕震模式分析

基于2011年以来云南地区59个GNSS测站的连续观测资料,计算面应变异常网格变化的时间序列,结合异常格网所在区域的动力学和地质构造背景、断层活动特性及震源机制等对区域异常的时空分布特征及地壳形变异常与地震事件之间的关系进行综合分析,并以2013-08-28发生的5.1级德钦地震为例验证基于应变时序孕震分析方法的有效性。结果表明,在宏观分析区域面应变长期背景特征的基础上,基于区域断裂活动性质和应变时间序列分析探讨面应变短期异常与地震事件之间关系的分析方法具有一定的科学合理性,能够在地震发震前夕得到有效的预报信号。     

基于大地测量观测的断层运动研究综述

以基于大地测量观测资料研究断层运动为主线,分析讨论地震大地测量观测资料在分析研究断层不同孕震周期运动模式中发挥的作用。回顾断层位错模型的发展,包括弹性回跳理论的提出、位错理论在描述同震、震间和震后形变中的发展应用,总结地震大地测量观测在判断断层孕震阶段中的应用,为断层地震危险性分析提供支撑。     

姚安Ms6.0地震典型重力前兆孕震模型量化研究

基于闭锁剪力模式与地震位错理论，提出构造“等效位错”来描述地震的震前“闭锁剪力”，并建立震前地表重力变化与“等效位错”之间的定量化模型。考虑到粗差干扰，采用稳健-贝叶斯最小二乘方法对姚安M_S6.0地震的“等效位错”进行反演。结果表明，其孕震源为高倾角走滑型，“孕震矩”与USGS给出的矩震级接近，证明该方法可依据震前重力四象限图像对未来震源特性和孕震强度进行预测。     

Analytical expressions for determining the stability of cohesionless soil slope under generalized seismic conditions

In recent major earthquakes, the researchers have found the need for consideration of vertical seismic acceleration for the stability analysis of the man-made and natural slopes. However, in most past studies, the performance of slopes has been assessed by accounting only the horizontal seismic component of the ground motion, without giving due weightage to the effect of vertical component. In the present study, analytical expressions are derived to determine the factor of safety, yield seismic coefficient and consequently the seismic displacement of cohesionless soil slope under combined horizontal and vertical components of the ground motion. The derivation uses the Newmark’s sliding block approach, in which the soil slope with a planar failure surface within the framework of conventional pseudo-static analysis is assumed to follow the Mohr-Coulomb failure criterion. The effects of vertical seismic coefficient on the stability of cohesionless slope have been studied through a set of graphical presentations for a specific range of soil parameters. It is observed that overlooking the effect of the vertical component of the ground motion on factor of safety and the displacement while designing the slope may be detrimental, resulting in the slope failure. The general expressions presented in this paper may be highly useful in the field of earthquake geotechnical engineering practice for designing the cohesionless soil slopes under combined horizontal and vertical seismic loads.     

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.     

基于地壳介质各向异性分析乳山地震近场区构造应力特征

利用乳山台阵和乳山台记录的资料,采用剪切波分裂方法分析乳山地区地壳各向异性参数,获得该区域应力环境特征。研究结果显示,乳山地区地壳介质各向异性受到区域构造应力和局部构造活动的双重影响,台站DSDC的快剪切波偏振优势方向近NW方向。结合地震序列展布方向及较大地震震源机制推测,该台附近存在近NW方向的活动断裂,该断裂可能为乳山地震序列的发震断层;台站BSTZ和CXZX的快剪切波偏振优势方向近EW方向,附近可能存在近EW方向的活动断裂。     

基于最邻近事件距离算法的华北地区地震丛集特征研究

利用华北地区2007年以来的地震资料,基于最邻近事件距离算法计算地震丛集率,对郯庐、燕山-渤海、河北平原、银川-河套、汾渭、淮河、长江下游-黄海等7个地震带进行地震丛集特征研究。对海城老震区的地震丛集特征分析认为,地震序列的丛集性明显减弱,目前发生的小震可视为反映区域应力状态的背景地震。以2015-04-15内蒙古阿拉善左旗5.8级地震为例,对华北地区显著中强地震前的地震丛集特征进行研究,发现中强地震前,地震丛集率在空间区域上先出现高值,随后出现低值,继而发震,对应地震活动中强震前增强-平静的现象,这一特征对判定未来潜在地震危险区有一定的指示意义。     

Continuum and discrete element coupling approach to analyzing seismic responses of a slope covered by deposits

Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problematic, however, to extend these approaches to the simulation of the slide, collapse and disintegration of the deposits under seismic loading. Contrary to this, a discrete element method (DEM) provides a means to consider large displacement and rotation of the non-continuum. To take the advantages of both methods of continuum and non-continuum analyses, seismic responses of a slope covered by deposits are studied by coupling a two-dimensional (2-D) finite difference method and a 2-D DEM, with the bedrock being modelled by the finite difference grids and the deposits being represented by disks. A smooth transition across the boundaries of the continuous/discontinuous domains is obtained by imposing the compatibility condition and equilibrium condition along their interfaces. In the course of computation, the same time-step value is chosen for both continuous and discontinuous domains. The free-field boundaries are adopted for lateral grids of bedrock domain to eliminate the radiation damping effect. When the static equilibrium under gravity load is obtained, dynamic calculation begins under excitation of the seismic wave input from the continuum model bottom. In this way, responses to the earthquake of a slope covered by deposits are analyzed dynamically. Combined with field monitoring data, deformation and stability of the slope are discussed. The effects of the relevant parameters of spectrum characteristic, duration, and peak acceleration of seismic waves are further investigated and explained from the simulations.     

鲁豫交界地区尾波Q_c值分析研究

该文对濮阳台记录的21次地震进行了地震波衰减研究,讨论了地球介质品质因子随频率变化的关系;利用不同地震采用不同流逝时间的尾波品质因子测定方法,有效去除了由于不同地震或同一地震的地震散射波在纵向介质中穿透深度的不同而导致对品质因子测量结果的影响,从而有利于扑捉到品质因子的异常变化特征与地震孕育过程的关系。利用改进后的模型,对鲁豫交界地区尾波值进行了计算,得到了该地区品质因子随频率的变化关系和区域介质衰减的时间变化特征。     

Seismotectonics of the Taiwan Shoal region in the northeastern South China Sea: Insights from the crustal structure

A cluster of earthquakes occurred in the Taiwan Shoal region on the outer rise of the Manila Trench. Although most were of small to medium magnitudes, one strong earthquake occurred on September 16, 1994. Several previous studies have provided important information to progress our understanding of this single earthquake. However, little is currently known about the earthquake cluster, and it is necessary to investigate the deep crustal structure of the Taiwan Shoal region to understand the mechanisms involved in controlling and generating it. This study presents a two-dimensional seismic tomographic image of the crustal structure along the OBS2012 profile based on ocean-bottom seismograph (OBS) data, which exhibits a high-velocity anomaly flanked by low-velocity anomalies in the upper crust beneath the Taiwan Shoal. In this study, 765 earthquakes (Richter magnitude M_L > 1.5) occurring between 1991 and 2015 were studied and analyses of earthquake epicenters, regional faults, and the crustal structure provides an improved understanding of the nature of active tectonics in this region. Results of analyses indicate firstly that the high-velocity area represents major asperities that correspond to the location of the earthquake cluster and where stress is concentrated. It is also depicted that the earthquake cluster was influenced by fault interactions. However, the September 1994 earthquake occurred independently of these seismic activities and was associated with reactivation of a preexisting fault. It is also determined that slab pull is resisted by the exposed precollision accretionary prism, and the resistive force is causing accumulation of inplane compressive-stress. This may trigger a future damaging earthquake in the Taiwan Shoal region.     

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.     

基于PhaseNet的地震信号自动处理方法准确性分析

利用一种深度学习地震信号检测方法（PhaseNet模型）检测甘肃省岷县MS6.6地震序列,根据地震震相关联技术和绝对定位Hypoinverse方法构建AI检测目录,对比人工分析地震目录和震相报告,分析AI自动处理地震事件的误差范围。结果表明,AI技术能够实现85.5%的人工工作量,定位误差在20 km范围内呈正态分布;在低震级地震事件检测中,AI方法也发挥了显著能力。相比于人工处理方法,AI方法稳定性好、不依赖个人经验、分析速度快,在大震后的地震目录快速产出中能发挥关键作用,可提高地震分析能力、节省人力成本。     

地震临界丛集的判定及其应用

介绍了地震临界时间丛集的判定方法——时间结构变异诊断方法。把时间结构变异诊断方法运用于1999年岫岩地震序列及中国大陆强震活动特性研究，并按此方法预测了中国大陆未来大震可能发生的时间点。研究认为，时间结构变异诊断法不仅可以用作前震序列和余震序列以及正常震群活动的判断，同时也适用于区域地震活动状态的描述。震例研究表明，时间结构变异诊断法在地震预测中具有实际意义。