基于广域次声传感器网络的地震本地次声波监测

通过提出应用于广域次声传感器阵列的最小方差法信号源定位模型, 分析了阵列信号相关系数特征和本地次声波实时大气传播特性, 对阵列阵元数量、阵元组成结构引起的定位误差以及本地次声波的真实大气传播射线进行仿真, 并利用中国境内布置的广域次声传感器网络监测到了2013年4月20日四川芦山(雅安)地震的瑞利波激发的本地次声波, 验证了上述模型和仿真, 结合中国地震台网的国内的地震监测台站数据, 从信号走时、信号互相关系数、小波时频图、质点运动轨迹等方面进行了分析与对比, 并使用广域最小方差法搜索的算法对次声波和地震波进行定位, 结果显示: 各次声站点接收到由地震瑞利波引起次声站附近地表震动产生并垂直地表向上传播的次声波, 在地震瑞利波之后到达, 而且相关系数都达到0.6~0.9, 计算得到次声波源方位角为230°(以北京为原点), 距离震中小于150 km, 而且本地次声波受大气传播影响较小, 能够较容易的被广域次声阵列探测到, 因此地震本地次声波监测能够作为地震监测、研究地面起伏运动与大气波动关系的有效手段.      

三峡库区巴东地震(Ms5.1)成因机制及次声波信号

2013年12月16日三峡库区巴东发生M_s5.1地震.根据eigen-6c2模型研究了巴东地区的8-638阶卫星重力异常, 结果表明: 该地区场源深度为10 km的地壳为局部重力低异常, 反映了该处物质密度较周围偏低, 形成低密度层.同时, 研究了该地区速度结构剖面, 结果表明: 巴东地区地壳5~9 km及10~15 km深处存在上下两个低速层, 上部低速层与水库渗水有关, 下部低速层与地幔热流体的上涌有关.低密度层和低速层的确定为韧性流变层的存在提供了证据.巴东地震是地壳深部能量的长期集聚与突发释放, 属构造地震.然而, 库水下渗引起的上部低速异常降低了断层活动的阈值, 震前库水载荷的变化对此次巴东地震的发生起到了触发作用.通过对比次声波和地震波, 我们得出次声波仪记录到的异常信号为本地次声波.      

Observation of abnormal thermal and infrasound signals prior to the earthquakes: a study on Bonin Island earthquake M7.8 (May 30, 2015)

Scientists from all over the world try to incorporate multi-disciplinary precursors to forecast the earthquake on a short-term basis. The authors here have analyzed outgoing longwave radiations acquired from polar-orbiting National Oceanic and Atmospheric Adminstration (NOAA) satellites and long-period infrasound waves recorded by the ground observatories in China prior to the recent Bonin Islands, Japan region earthquake which occurred on May 30, 2015 with the magnitude of 7.8. The anomalous outgoing longwave radiation (OLR) was observed on May 15, 2015, and was recorded by “NOAA 18” satellite during its “night pass.” Similarly, an abnormal infrasound spike was recorded at the Beijing station on May 17, 2015. The delay in observing anomalous infrasound waves compared to the OLR anomaly is due to these low-frequency waves traveling at low speed with the velocity range of 10–15 m/s. From the analysis of the results, it can be inferred that there is a substantial relation between parameters like OLR and infrasound waves; hence, the authors conclude that it is possible to forecast the earthquake on a short-term basis with reasonable accuracy.     

Automatic detection of avalanches: evaluation of three different approaches

Automated detection of snow avalanches is an important tool for avalanche forecasting and for assessing the effectiveness of avalanche control measures at bad visibility. Avalanche detection systems are usually based on infrasound, seismic, or radar signals. Within this study, we compared three different types of avalanche detection systems: one avalanche radar, one infrasound array system consisting of four infrasound sensors, and a newly developed single sensor infrasound system. A special focus is given to the new single sensor system, which is a low cost, easy to install system, originally designed for the detection of debris flows and debris floods. Within this work, we analysed how this single sensor system could be adapted to detect also snow avalanches. All three systems were installed close to a road near Ischgl (Tyrol, Austria) at the avalanche-exposed Paznaun Valley. The valley is endangered by two avalanche paths which are controlled by several avalanche towers. The radar system detected avalanches accurately and reliably but was limited to the particular avalanche path towards which the radar beam was directed. The infrasound array could detect avalanches from all surrounding avalanche paths, however, with a higher effort for installation. The newly tested single infrasound sensor system was significantly cheaper and easier to install than the other two systems. It could also detect avalanches form all directions, although without information about the direction. In summary, each of the three different systems was able to successfully detect avalanches and had its particular strengths and weaknesses, which should be considered according to the specific requirements of a particular practical application.     

Monochromatic infra-sound waves recorded offshore Ecuador: possible evidence of methane release

ABSTRACT Methane is known to be a greenhouse gas but it is difficult to estimate its significance. We have identified a new approach for monitoring fluxes of methane from large areas of sea floor. During spring 1998, we conducted an offshore passive seismic experiment using 13 three-component digital Ocean Bottom Seismometers. During this 3-week experiment, we recorded unusual sustained and intense monochromatic infrasound waves (6–7 Hz). The origin of the noise is tentatively interpreted as pressure-waves resulting from oscillating clouds of bubbles. Such clouds must have a characteristic size of ∼ 10 m, at depths of 5–15 m, and must contain more than 10¹⁰ bubbles of 1 mm radius to produce the observed frequency. The presence of a Bottom Simulating Reflector in the study area suggests that gas seepage may occur at the seafloor, near 500 m depth. Then, bubbles of gas, namely methane, could form in the water column. Although highly speculative, Ocean Bottom Seismometer records could potentially be useful for monitoring gas seeps and/or related unusual behaviour of the seabed.     

地下综合管廊地震动力响应三维数值分析

综合管廊由于埋深较浅,在抗震分析中应考虑Rayleigh波的作用,为研究Rayleigh波与底部地震加速度共同作用下综合管廊的动力响应特征,建立双仓的综合管廊三维动力有限元数值模型,土体采用考虑滞回环特性的高级本构模型（HSS模型）,通过边界上多次脉冲荷载生成Rayleigh波,模型底部横向分别作用Upland波、Kobe波、Taft波,并与仅考虑底部横向作用的常规时程分析进行对比。研究表明:综合管廊结构的横向动力响应主要受横向地震波影响,结构纵向动力响应受沿其轴向入射的Rayleigh波影响相对较大;采用Rayleigh波+底部地震波的输入方法比单独底部地震波输入得到的结构动力响应整体上要更显著一些;输入不同的地震加速度时程,管廊动力反应规律相似,但综合管廊结构影响大小有差异,可见底部地震波与地表Rayleigh波作用的匹配程度对结构动力响应结果有一定影响。研究成果可供地下综合管廊结构地震动力响应精细化数值分析及抗震设计参考。     

基于时频域极化滤波的勒夫型槽波提取

矿井槽波地震勘探数据中,含有多种类型地震波,包括线性极化的纵波、横波、勒夫型槽波和椭圆极化的瑞利型槽波。由于槽波频散现象严重,不同类型槽波互相重叠,在地震记录上难以区分,合理地进行波场分离是槽波数据处理的重要环节。根据不同类型槽波振动极化特征,提出基于S变换的时频域自适应协方差矩阵极化滤波方法;在时频域中,针对槽波水平双分量信号建立自适应协方差矩阵;利用矩阵对应特征值和特征向量,计算椭圆率和方位角参数来描述槽波极化振动特征;依据极化参数建立极化滤波函数,对槽波地震信号进行波场分离。经过理论合成信号和实际数据测试表明,该方法可以有效地从槽波地震记录中提取出勒夫型槽波,避免其它类型地震波在槽波数据处理过程中产生的干扰,为槽波地震勘探数据处理提供新的技术手段。      

提高叠加地震波分辨率的一种反演方法

子波提取是采用优化快速模拟退火法进行反演，提高叠加地震波分辨率的关键。本文应用最小平方法计算在合成地震记录与井旁地震记录差平方条件下的地震子波，制作合成地震记录，并进行反演以达到提高信噪比的目的。这是一种通过钻井资料来去噪、提高地震分辨率的方法，该方法原理简单、使用方便、效果较理想，有推广的意义。     

煤炭地震激发介质与井深的关系

通过地震波在近地表附近双源传递机理的研究,论述了近地表介质与激发井深的关系,研究了利用地震波最大激发能量与地震波最大信噪比选择爆破源地震激发井深的方法。三维地震实例研究结果表明,地震波在近地表附近的双源传递与品质因数是选择地震波的激发井深的重要因素。从实例结果来看,该方法不仅取得了高质量的勘探成果,而且节约了采集费用。     

不耦合装药爆破对硬岩应力场影响的数值分析

爆破地震勘探石油是一种重要的方法,但爆破地震效应与爆破参数、地质条件等密切相关。采用动力有限元软件ANSYS/LS-DYNA,对柱状炸药与药孔壁之间为空气或其他介质以及空隙间距变化时碳酸盐岩岩石中爆炸应力波的传播规律和爆炸地震波能量的衰减特性进行了数值模拟研究,得到了不耦合装药爆炸时岩石应力、振动速度的衰减规律以及与不耦合系数、间隙介质的关系,分析了不耦合效应对爆炸地震波能量的影响。研究表明,不耦合或耦合不好时会使岩体中爆炸应力波的强度大大降低;耦合状态对岩体应力及速度的衰减系数和衰减指数影响较大;在空隙中注水或灌满泥浆会改善它们的耦合关系,增大下传的爆破能量。所得成果可为我国西南地区优选适合碳酸盐地层地震勘探的激发因素提供技术途径和方法。     

不同压实度铁路路堤边坡地震响应振动台试验研究

为研究和对比不同压实度铁路路堤边坡的地震响应,设计了路堤本体压实度分别为95%、91%、87%和83%的4组路堤边坡模型,开展了不同压实度路堤边坡的振动台试验研究。通过穿插进行白噪声激励得到不同压实度路堤边坡的动力特性参数;通过施加不同类型和不同强度的地震动激励,研究不同压实度路堤边坡加速度放大倍数分布规律及其影响因素。结果表明,随着地震动激励次数的增多,路堤边坡自振频率下降,阻尼比增大,压实度对路堤边坡动力特性变化影响显著;加速度放大倍数沿路堤边坡高度呈非线性增大,加速度放大倍数随地震动激励强度增大而减小;台面输入的地震波经路堤边坡传播后,其频谱特性发生了明显的变化,不同压实度路堤边坡对地震波频谱特性的影响不同;不同地震动激励下不同压实度路堤边坡的加速度放大倍数分布情况有所差异,这与地震动频谱特性和路堤边坡动力特性参数有关     

建立地震发射台的建议

目前地球上有成千上万个地震台，但它们都是接收地震波的地震台。建议建立一种新型的地震台，这种地震台用人工的方法不断地向外发射地震波，照亮需要研究地区的地下结构，研究特定的科学问题。建立地震发射台的核心问题是选择合适的人工震源，近年来出现的绿色环保震源，以及现代信息处理技术的发展，使得建立照亮10万km2(深至Moho面)地区地下结构的地震发射台已经完全是可能的。     

SV波入射下峡谷地形对多支撑大跨桥梁地震反应影响分析

以二维河谷地形在SV波垂直入射和斜入射下的结果作为地震动输入,分析了地形因素导致的地震动差异对一座桥墩高差悬殊的连续刚构桥地震反应的影响,并与一致激励下的结果进行了对比。结果表明：与一致激励相比,考虑地形效应的多点激励作用下,刚构桥地震反应存在显著差异,难以找到规律性,不同的结构部位其最大内力的表现各不一样;多点激励使主梁遭受不利反应;斜入射对低墩和主梁有显著影响,使其内力显著增加或使结构各部位内力分布明显不均衡;与低墩相比,高柔的桥墩对多点激励相对不敏感;大跨度桥梁抗震分析与设计应考虑局部场地和入射波的入射方向和角度的影响     

地下综合管廊边界条件对地震动力响应影响数值分析

为研究综合管廊动力边界条件对地震动力响应的影响,以厦门地区的代表性土层为例,建立动力有限元数值模型,土体本构采用小应变硬化模型,分别设定固定边界、黏性边界和自由场3种人工边界条件,进行Rayleigh波和地震底部剪切波作用下的场地响应研究;并根据变形特征及拟绝对加速度反应谱（PSA）评价3种边界的有效性,提出综合管廊地震动力分析的优化动力边界组合方法。研究表明：在地震波（底部水平加速度时程）及Rayleigh波的作用下,由于考虑了黏性边界对外行波的吸收,但未考虑地震动的输入问题及边界外半无限介质的弹性恢复性能,边界会对模型内部土体的水平位移产生限制作用,使得场地内水平位移响应偏小,而采用自由场边界则基本不存在这种限制作用,表现出强烈的振荡;采用激励侧固定边界、远离激励侧黏性边界、其余侧自由场边界的优化组合动力边界,在Rayleigh波和底部加速度时程共同作用下,二者引起的动力响应交叉干扰较少,可按线性叠加处理;同时,黏性边界对地震波引起的动力响应有一定范围的吸收,自由场边界对Rayleigh波引起的动力响应也有一定范围的变形限制影响。研究成果可供地下综合管廊结构地震响应精细化数值模拟及抗震设计参考。     

差异散射多次波自适应消减法研究

在海上地震资料处理过程中,反射多次波和散射多次波同时存在于地震资料中。由于散射多次波相对于反射多次波的能量弱,且具有时空非稳态特征,难以在常规SRME 方法中去除,影响进一步的数据分析工作。将含有这两种多次波的地震数据进行分离并分别做SRME 多次波预测,通过自适应衰减方法有效地匹配不同类型多次波,尤其是非稳态的散射多次波。通过sigsbee2B 模型的试算,经对比理想无多次波影响的地震数据资料,表明该方法可以有效地同时消除反射多次波和差异散射多次波。     

New Method to Compute Seismic Active Earth Pressure on Retaining Wall Considering Seismic Waves

In earthquake prone areas, calculation of seismic active earth pressure on retaining wall is very important. Analytical methods till date for computation of seismic active earth pressure do not consider the effect of Rayleigh wave though it constitutes about 67 % of the total seismic energy. In this paper a new dynamic approach is proposed by considering all possible seismic waves viz. primary, shear and Rayleigh waves for estimation of seismic active earth pressure on rigid retaining wall by satisfying all the boundary conditions. Limit equilibrium method is used for estimation of optimised seismic active earth pressure for a rigid retaining wall supporting cohesionless backfill with critical combinations of seismic accelerations. The seismic influence zone obtained in this study is about 22 and 17 % larger when compared with available pseudo-static and pseudo-dynamic methods respectively, which indicates the significant effect of Rayleigh wave. Also, there is an increase of about 14 and 6 % in seismic active earth pressure coefficient when the present results are typically compared with pseudo-static and pseudo-dynamic methods respectively. Moreover present results compare well with the available experimental results. Present results are more critical for the design estimation of seismic active earth pressure by considering all major seismic waves as proposed in the new dynamic approach.     

工程场地土层地震反应模型实例分析

在给定基岩地震输入的情况下计算实际场地土层不同深处的地震动反应谱,然后修改实际土层模型参数,在考虑土层厚度和软弱夹层变化的情况下进行地震反应分析,得出一些有意义的结论。     

Analysis of Stochastic Seismic Wave Interaction with a Slippery Rock Fault

Stochastic seismic wave interaction with a slippery rock fault is studied, based on the principle of conservation of momentum at the wave fronts along the fault. By using the displacement discontinuity method, the wave propagation equations are derived for incident longitudinal-(P-) and shear-(S-) waves, respectively. This is an extension of the study by Li and Ma (2010) for blast-induced wave propagation across a linear rock joint. Stochastic seismic waves are generated from a frequency spectrum and used to analyze the seismic wave interaction with a rock fault having a Coulomb-slip behavior. Parametric studies are carried out to investigate the effect of the intensity and impinging angle of the incident seismic waves on wave propagation across a slippery rock fault. Results show that the transmission of the incident P-wave is almost not affected by the fault, on the contrary, this is not the case for an incident S-wave, due to the occurrence of a relative slip which is related to the impinging angle of the incident S-wave. A quantitative study is presented which is of help in understanding the propagation and attenuation laws of seismic waves in discontinuous rock masses.     

地球各向异性介质中地震波动理论、检测与应用研究

地下岩石的各向异性主要表现在地震波速度随传播方向发生变化,不同类型体波间相互耦合,横波发生分裂,波速度频散依赖于传播方向等。薄互层与裂隙定向分布等产生视各向异性,它在石油地震勘探、地震预测和岩石圈物理与动力学研究中有极大潜力和应用前景,并受到广泛重视。为此,文中讨论了地震各向异性研究在解决地球科学问题中的重要性与必要性;系统地介绍了中国在地震各向异性研究领域的各个方面,如波动传播、波场激发、数值模拟、偏移与反演成像,以及应用于油气资源探测、深部地球物理研究和地质灾害监测等方面所取得的新进展。结合笔者参加的第八届地震各向异性国际学术讨论会,及ＳＥＧ,ＩＡＳＰＥＩ,ＩＵＧＧ等有关学术会议情况,综述了国际上在该领域内的主要成果与发展动向,分析了国际上各国地震各向异性研究现状及存在问题,并对我国在该领域研究的进一步开展提供了主攻问题与相应建议。     

多次波正演与SRME技术影响因素分析及应用

针对深水采集的地震数据包含严重的多次波,多次波与有效波互相叠合使得地震剖面的同相轴难以区分和追踪解释的情况,采用实际资料的层位,建立三维地质模型并用实际的导航数据正演模拟野外放炮施工,由于正演模拟的数据层位较少,可针对性地分析三维SRME技术预测多次波模型的影响因素,如空间采样、扩展半径等,然后应用于实际地震数据的SRME处理,比较二维SRME与三维SRME的应用效果,验证了三维SRME比二维SRME能更有效地衰减多次波。