Research on angle-dependent to mographic static correction

Reflection data in CMP has influenced seriously in static calculations,especially in some highly weathered and structurally altered circumstances. Because of static correction in the existed problems and requests,the authors studied the angle dependent tomographic static correction,and discussed its basic theory, including the establishment of forward model,the calculation theory of tomography and tomographic static correction. The usage of theoretical models and practical information on the method has been validated. The results show that using these methods to calculate static correction in a complex area,the quality of static correction is greatly improved.     

Surface wave tomography of the western United States from ambient seismic noise: Rayleigh and Love wave phase velocity maps

We present the results of Rayleigh wave and Love wave phase velocity tomography in the western United States using ambient seismic noise observed at over 250 broad-band stations from the EarthScope/USArray Transportable Array and regional networks. All available three-component time-series for the 12-month span between 2005 November 1 and 2006 October 31 have been cross-correlated to yield estimated empirical Rayleigh and Love wave Green's functions. The Love wave signals were observed with higher average signal-to-noise ratio (SNR) than Rayleigh wave signals and hence cannot be fully explained by the scattering of Rayleigh waves. Phase velocity dispersion curves for both Rayleigh and Love waves between 5 and 40 speriod were measured for each interstation path by applying frequency–time analysis. The average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station-triplets. We find that empirical Green's functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross-correlation without explicit knowledge of the source distribution. The average traveltime uncertainty is less than 1 s at periods shorter than 24 s. We present Rayleigh and Love wave phase speed maps at periods of 8, 12, 16,and 20 s. The maps show clear correlations with major geological structures and qualitative agreement with previous results based on Rayleigh wave group speeds.     

Cross-dependence of finite-frequency compressional waveforms to shear seismic wave speeds

Seismic tomography has been one of the primary tools to image the interior of the earth and other elastic structures. To date the inversions of compressional ( P ) and shear ( S ) wave speeds have been carried out separately under the assumption that P traveltimes are affected only by the P wave speed of the elastic media and S traveltimes by the S wave speed. Using numerical and analytical solutions, we show that for finite-frequency seismic waves, S wave speed perturbations may have significant effects on P waveforms. This suggests that when waveform-derived traveltime and amplitude anomalies are used in tomographic inversions, the P -wave measurements should be related to not only P wave speed perturbations but also S wave speed perturbations.     

The shear-wave velocity structure in the upper mantle beneath Eurasia

We develop an approach that allows us to invert for the mantle velocity structure within a finely parametrized region as a perturbation with respect to a low-resolution, global tomographic model. We implement this technique to investigate the upper-mantle structure beneath Eurasia and present a new model of shear wave velocity, parametrized laterally using spherical splines with ∼2.9° spacing in Eurasia and ∼11.5° spacing elsewhere. The model is obtained from a combined data set of surface wave phase velocities, long-period waveforms and body-wave traveltimes. We identify many features as narrow as few hundred kilometres in diameter, such as subducting slabs in eastern Eurasia and slow-velocity anomalies beneath tectonically active regions. In contrast to regional studies in which these features have been identified, our model encompasses the structure of the entire Eurasian continent. Furthermore, including mantle- and body-wave waveforms helped us constrain structures at depths larger than 250 km, which are poorly resolved in earlier models. We find that up to +9 per cent faster-than-average anomalies within the uppermost ∼200 km of the mantle beneath cratons and some orogenic regions are separated by a sharp gradient zone from deeper, +1 to +2 per cent anomalies. We speculate that this gradient zone may represent a boundary separating the lithosphere from the continental root, which might be compositionally distinct from the overlying lithosphere and remain stable either due to its compositional buoyancy or due to higher viscosity compared with the suboceanic mantle. Our regional model of anisotropy is not significantly different from the global one.     

气体水合物生成实验过程动态监测:一种新的ERT方法及其效果分析

现阶段适用于天然气水合物资源开采过程获得其空间分布变化的现场监测技术仍不完善.以电阻率层析成像(ERT)技术为基础,研发一套新的ERT阵列(由两组平行的垂向电极组合而成,每组阵列有24个环形电极)应用于水合物储层动态变化监测模拟实验.通过开展物理模拟实验,采用新的E RT方法对水合物生成过程进行了动态监测,并分析了动态...     

钉形水泥土双向搅拌桩加固软土地基的效果分析

针对水泥土搅拌桩应用中存在的问题,介绍了最新研制的钉形水泥土双向搅拌桩及其施工工艺。施工质量检验表明,钉形水泥土双向搅拌桩桩体质量好于常规水泥土搅拌桩,钉形水泥土双向搅拌桩单桩及复合地基承载力分别较常规水泥土搅拌桩的单桩及复合地基承载力有较大提高。通过对试验段的观测成果分析,论证了钉形水泥土双向搅拌桩加固软土地基优越的工程特性。     

Determination of the 3D structure of an earthflow by geophysical methods: The case of Super Sauze, in the French southern Alps

In order to evaluate the risk associated by an earthflow to abruptly evolve into a torrential flow, the knowledge of its internal structure is necessary. Geotechnical methods are important to reach this goal. However, because of the rough topography associated with earthflows, their surface heterogeneities, and the spatial variations of the thickness of the potentially moving mass, non-intrusive geophysical methods offer a very useful tool that complements traditional geotechnical methods. We report the results of a comprehensive study covering a 150 m by 200 m area of the Super Sauze earthflow. This earthflow developed in black marls in the southern French Alps. Shallow electrical conductivity investigations, derived using low frequency domain electromagnetics, maps hidden gullies and crests and lateral variations of the clay and the water content within the first 5 m below the ground surface. Electrical resistivity tomography allows to extrapolate this information down to 10 m below the ground surface along selected transects. The vertical structure of the earthflow, down to the substratum, is defined precisely thanks to joint inversion of DC and TDEM vertical soundings along one profile: the flowing upper layer and the position of the substratum are clearly evidenced. Combining this geophysical datasets with geotechnical tests and drill holes, we provide an estimate of both the location and the volume of the potentially most dangerous areas of the earthflow.