地震勘探中广义弹性阻抗的正反演

常规的地震道反演方法建立在反射P波垂直入射假设 的基础上,而实际地震资料采集时多数是非零炮检距的，反射振幅是共中心点道集叠加的结 果 . 因此，利用常规地震道反演方法就不能得到可靠的波阻抗或其他岩性信息. 本文利用Patr ick Connolly弹性阻抗的思想，通过对Zoeppritz方程的进一步简化，推导出适合常规叠后 资料的、非零炮检距条件下纵波反射系数递推公式，提出了广义弹性阻抗的概念，解决了非 零炮检距条件下，常规叠后地震道正反演的关键问题. 广义弹性阻抗不仅包含波阻抗，还包 含了纵横波速度等岩性信息，具有很好的实用价值. 进行广义弹性阻抗的反演，能较常规地 震道反演获得更多、更可靠的流体、孔隙度、砂泥含量等信息，有助于解释常规地震道反演 和道积分剖面中的假象，降低反演的多解性，提高储层预测的精度.     

Foundation settlement statistics via finite element analysis

The dispersion observed in soil data comes both from the spatial variability which greatly influences the behavior of large structures and from errors in testing. Thus, the geotechnical engineering deals with uncertainties for which deterministic approaches are not suitable. The resort to probabilistic techniques, enables modeling uncertainties by analyzing their dispersion effect on the global behavior of the structure. The scope of this paper is analyzing settlement and differential settlement variability of a pair of foundations on random heterogeneous medium. The random soil properties of interest are the elastic modulus, and the Poisson ratio. The elastic modulus is modeled as a spatially random field by adopting the lognormal distribution, which enables analyzing its large variability. Because soil Poisson ratio is bounded in practice between two extreme values, its random field is obtained by using the Beta distribution. In this study, one proposes for the Beta field determination, a mapping technique on the probability distribution function diagram, by solving a non-linear equation. However, the mean and variance are unchanged through the mapping operation. Because the soil Poisson ratio is a positive parameter, one prefers to perform the mapping operation with the probability function of the lognormal distribution. Also, the proposed technique can be used for other bounded soil properties such as the porosity. In this paper, settlement and differential settlement statistics prediction are carried out using Monte Carlo simulations combined with deterministic finite element method (DFEM). A performed parametric study shows the following: (i) as the variability of the elastic modulus increases as settlement and differential settlement statistics are important, also, settlement statistics decreases as the Poisson ratio variability increases, and differential settlement statistics do not seem be affected by its variability. (ii) settlement and differential settlement statistics are important for positive inter-property correlation. (iii) a great influence of the correlation lengths on settlement and differential settlement statistics.     

Ab initio elasticity of FeS2 pyrite from 0 to 135 GPa

Polynomial expressions for the elastic tensor coefficients, the bulk, the shear and Young’s moduli, the speed of sound for longitudinal and transverse waves, the equation of state and the x coordinate of the sulfur atom in pyrite are reported based on ab initio calculations in the range of 0–135 GPa. Comparison with published experimental data indicates good agreement for the equation of state and for values at 0 GPa as well as reasonable agreement for first derivatives. All modeling and interpretation was performed with Materials Toolkit v.2.0 and all ab initio computations with VASP.     

Microcosmic analysis of ductile shearing zones of coal seams of brittle deformation domain in superficial lithosphere

For many years, the study on ductile shearing zones mainly focuses on the strain analysis and the characteristics of microcosmic structure of felsic duc-tile shearing zones in deep layers (8—10 km). Discus-sions on the process of the development of small-type and mini-size ductile shearing zones have been re-ported in recent years[1,2]. 揇uctile deformations in brittle deformation擺3] and 揵rittle deformations in ductile deformation擺4] are rather a familiar phenome-non in nature. Researchin…     

Control on seafloor spreading geometries by stress- and strain-induced lithospheric weakening

Seafloor spreading typically occurs along ridge segments oriented at right angles to plate motion and offset by orthogonal transform faults. Few regions exhibit different patterns, such as the East Pacific Rise (EPR), which additionally displays overlapping spreading centres (OSCs) and microplates. We introduce a dynamical model using two independent, scalar types of damage in an elastic plate that generates most observed spreading geometries as natural failure modes, suggesting that the dynamics of the underlying mantle have only a minor influence on accretionary plate margins. The elastic modulus that is affected by the damage determines the type of localized deformation. Damage reducing the bulk modulus tends to result in tensile fractures, while a reduction in shear modulus leads to shear fractures. The damage source determines the fracture orientation. Material weakening in tension results in fractures perpendicular to the most tensile principal stress, while shear weakening results in two conjugate fractures at 45° relative to the applied stress. Strain or energy-dependent damage results in propagating, localized fractures. Stress-dependent damage tends to evolve into diffuse regions that may eventually focus into narrow zones. Starting from small perturbations with reduced elastic moduli as nucleation points, all ridge geometries start with ridge propagation caused by tensile energy reducing both elastic moduli by a model of damage caused by tensile energy reducing both moduli. Orthogonal transform faults develop in regions between offset segments if there is an additional reduction in shear modulus due to shear stress. The orthogonality of the transform faults does not derive from the local stress orientation but from the dynamics of damage focusing which causes the fault to converge towards an optimal geometry that concentrates nearly all deformation into damaged zones. OSCs form when the shear damage leading to transform faults is suppressed, while microplate formation requires additional reduction of the shear modulus by tensile energy. Oblique spreading at 45°, recently discovered along ultraslow spreading ridges, occurs when both moduli are weakened by shear energy. A parameter regime exists in which ridge-transform patterns develop at low applied tension, while microplates form at higher stresses. These results indicate that at least three different micromechanical processes operate with different evolution rates. OSCs and oblique spreading require different material properties.     

单层纵弯褶皱曲率指数与应力指数的关系探讨

褶皱含有岩石经历的变形和变形条件的信息。力学、数学、数值和实验分析显示，通过分析单层纵弯褶皱的形态可获得流变学信息。数值模拟表明褶皱的曲率指数ｋｉ对于应力指数ｎｌ有很好的依赖性，当波长厚度比λ／ｈ≥１０时，ｋｉ随着ｎｌ的增加而增加。基于数值模拟的结论，分析了北京西山板岩中石英脉肠状褶皱，获得了石英脉的应力指数大于１０的结果，并进而获得石英脉对板岩的粘度比在２４１～６６２之间。认为这种小构造的研究方法是一个新的获取岩石流变参数的可行途径     

Rheology and seismotectonic regime in the northern central Mediterranean

The connection between thermal field and mechanical properties is analysed in the northern central Mediterranean region, extending from the Ligurian-Provençal basin to the Adriatic foredeep. As the thermal regime is still far from equilibrium in most of the tectonic units, transient thermal models are used. The temperature-depth distribution is estimated in four areas affected by the volcanic activity, which from the Neogene to the Present shifted from Corsica to the Apenninic arc. In the Adriatic foredeep, the thermal effects of the recent thrust-faulting phase in the buried sectors of the northern Apennines are taken into account.

The general context consists of convergence involving westward subduction of the Adriatic plate. This process caused anti-clockwise rotation of Corsica and Sardinia, which led to formation of the Ligurian marginal basin, and also resulted in crustal doubling and overthrusting in the northern Apennines and rifting in the northern Tyrrhenian.

Seismic activity is focused in the internal and external zones of the Apenninic arc, where low surface heat flux is observed, and in the western margin of the Ligurian-Provençal basin. This is a consequence not only of lateral variations in the thermal field but also of the different tectonic settings. Regional extensional patterns in the shallow crust, with minimum principal stress axes trending N60°E and E-W, are observed in the northern and in the southern sectors of the Apenninic arc, respectively. A compressional regime at depths greater than 30 km is observed below the northern sector of the arc, while to the south a change in the structure of the lithosphere is marked by a decrease in deeper seismic activity. Thrust faults and strike-slip faults with a thrust component support a compressional regime along the western margin of the Ligurian basin with maximum principal stress axis oriented N120°E.

Two lithospheric cross-sections across the study region are constructed, based on structural, thermal, gravity, rheological and seismic data. There is clear evidence of the presence of the subducting slab of the Adriatic plate, corresponding to a thickening of the uppermost brittle layer. The crustal seismicity cut-off corresponds to temperatures of 320–390°C. A brittle layer of considerable thickness is present in the uppermost mantle beneath Variscan Corsica and the Adriatic foredeep, with estimated seismic cut-off temperature of about 550 ± 50°C.