Azimuthal variation of the P phase in Icelandic receiver functions

A curious observation has been made on radial receiver functions calculated from teleseisms recorded by 29 broad-band seismometers distributed over Iceland. The arrival time of the direct P phase of the radial receiver functions depends critically upon the azimuth of the teleseismic source. For a seismic station in West Iceland, the direct P  phase of the radial receiver function arrives consistently later for easterly source azimuths than for westerly source azimuths. The reverse applies for stations in East Iceland. In the original seismograms, the delayed P phase of the receiver function appears up to 450 ms later on the radial than on the vertical component. The seismometer locations in East and West Iceland are separated by the Neovolcanic Zone, a constructive plate boundary. The delayed P phases occur for seismic rays travelling across this zone. However, it is not obvious how wave propagation across the plate boundary zone could cause the observed delays. The tentative explanation proposed here involves the regional dip of the Icelandic lava sequences towards the Neovolcanic Zone. A dipping interface at shallow depth results in a P–S converted phase arriving shortly after the P phase. These phases cannot be separated in the radial receiver functions, given the bandwidth of the observed signals. However, a calculation of receiver functions from estimates of the P , SV and SH wavefields clearly reveals a P–S converted phase at about 500 ms for easterly source azimuths in West Iceland and for westerly source azimuths in East Iceland. The amplitudes of the direct P phase and the P–S phase converted at a dipping interface would be expected to vary strongly with azimuth in accordance with the observed behaviour.     

金属矿地震散射波场的数值模拟研究

地震方法用于寻找石油、煤田等沉积层控矿床已取得许多成功经验和大量的成果；对于金属矿可依据微扰理论，通过地震波散射响应的强弱推断矿体。模拟实验结果表明，散射波相干性的好坏与杂乱散射体的不均匀性有关；不均匀性越强，产生的散射相干性就越好。     

Smooth constraint inversion technique in genetic algorithms and its application to surface wave study in the Tibetan Plateau

IntroductionThe dispersion phenomena, which can be observed when surface wave travels through the Earth interior, has been extensively applied in investigating the velocity structure of the Earth interior. Usually, the dispersion curve is a nonlinear function of the thickness, S and P wave velocities and density of each layer. Because surface wave inversion is a multiple-minima problem, the result strongly depends on the initial model in traditional linear inversion. Genetic algorithm (GA) …     

Three-dimensional Q structure in Jiashi earthquake region of Xinjiang

3-D S-waveQ structure in Jiashi earthquake region is inverted based on the attenuation of seismic waves recorded from earthquakes in this region in 1998 by the Research Center of Exploration Geophysics (RCEG), CSB, and a rough configuration of deep crustal faults in the earthquake region is presented. First, amplitude spectra of S-waves are extracted from 450 carefully-chosen earthquake records, called observed amplitude spectra. Then, after instrumental and site effect correction, theoretical amplitude spectra are made to fit observed amplitude spectra with nonlinear damped least-squares method to get the observed travel time overQ, provided that earthquake sources conform to Brune’s disk dislocation model. Finally, by 3-D ray tracing method, theoretical travel time overQ is made to fit observed travel time overQ with nonlinear damped least-squares method. In the course of fitting, the velocity model, which is obtained by 3-D travel time tomography, remains unchanged, while onlyQ model is modified. When fitting came to the given accuracy, the ultimateQ model is obtained. The result shows that an NE-trending lowQ zone exists at the depths of 10–18 km, and an NW-trending lowQ zone exists at the depths of 12–18 km. These roughly coincide with the NE-trending and the NW-trending low velocity zones revealed by other scientists. The difference is that the lowQ zones have a wider range than the low velocity zones. Foundation item: Joint Seismological Science Foundation of China (957-07-414) and State Key Basic Research Development and Programming Project (95-13-02-02). Contribution No. RCEG200105, Research Center of Exploration Geophysics, China Seismological Bureau.     

滞回曲线对应力振幅和频率的响应

基于疲劳载荷对应力－应变滞回曲线的影响，作者研究了滞回曲线对应力振幅和频率的影响，获得了载荷超过屈服点后应力振幅增大，滞回曲线趋于稳定，应变硬化效应增强的结果，随着正弦波频率增加岩石的滞回圈频散效应增强，饱和液体加强了这种频散作用，随孔隙液体的粘滞系数增大，滞回曲线的频散效应更强。     

多波勘探技术在地下隐蔽物探测中的应用

近年来，多波勘探技术已广泛地应用到工程地质的各个领域，它以其快速有效及低廉的工作成本，受到广大工程地质人员的欢迎。在中关村地下粮库和人防工程探测中，采用了高密度地震影像法和多道瞬态瑞雷波法，取得了良好的应用效果，为地下隐蔽物的探测提供了一种新的方案。     

用转换波检测煤层裂隙的方法探讨

根据理论模型计算结果对比分析找出的煤层纵波场和转换波场和转换波场与煤层裂隙状态变化间的相关关系，探讨了综合使用纵波和转换波检测煤层裂隙的可行方法，对有效开展转换法地震勘探工作具有指导意义。     

地下工程震波技术与应用

激发的震波在工程岩土体中传播，检测其波动力学参数，来测试岩土体的工程力学性质。原位震波波速测试技术可以对井巷的岩体模量，支护选型，围岩性质进行检测；利用地震勘探，面波勘探方法可以对矿层厚度，超前探测等方面进行有效检测；震波CT、导波勘探等探测方法对于采面内的地质异常探测有较好的针对性；通过声发射检测技术可以解决地下工程安全问题。实际应用说明，震波探测技术从地下工程的开拓掘进，采场形成到采后管理等过程中有着广泛的应用前景。一些技术已作为地下工程中的日常工作加以应用，但进一步的生产应用还需深入研究。     

对粉喷桩检验方法的认识和探讨

介绍了检验复合地基承裁力及桩身完整性的主要方法静裁荷试验、低应变反射波法，并对检测应满足的前提条件进行了认识和探讨。     

合成平面波数据的Rytov近似叠前深度偏移

作者把Berkhout(1992)提出的合成平面波技术应用于线性Rytov近似叠前深度偏移，提高了波动方程叠前深度偏移的计算效率。通过在Marmousi模型数据试验，我们认为在达到基本相同成像效果的条件下，利用合成平面波技术的波动方程叠前深度偏移相对于基本共炮集数据的波动方程叠前深度偏移可提高计算效率约10倍。