印度与欧亚板块强烈相互作用区深部结构特征研究

The central-south Tibet is a part of the products of the continental plate collision between Eurasia and India. To study the deep structure of the study area is significant for understanding the dynamics of the continental-continental collision. A 3-D density model matched well with the observations in the central-south Tibet was proposed in this study. In addition, this study has also used numerical simulation method to prove that Quasi-Love (QL) wave is deduced by anisotropy variation but not by lateral heterogeneity. Meanwhile, anisotropy variation in the upper mantle of the Qiangtang terrane and Lhasa terrane is detected by the QL waves observed in recorded seismograms. Based on the gravity modeling, some results are summarized as follows: 1) Under the constrain of geometrical structure detected by seismic data, a 3-D density model and Moho interface are proposed by gravity inversion of the central-south Tibet. 2) The fact that the lower crustal densities are smaller than 3.2 g/cm3, suggests absence of eclogite or partial eclogitization due to delamination under the central-south Tibet. 3) Seismicity will be strong or weak in the most negative Bouguer gravity anomaly. So there is no a certain relationship between seismicity and Bouguer gravity anomaly. 4) Crustal composition are determined after temperature-pressure calibration of seismic P wave velocity. The composition of lower crust might be one or a mixture of: 1. amphibolite and greenschist facies basalt beneath the Qiangtang terrane; 2. gabbro-norite-troctolite and mafic granulite beneath the Lhasa terrane. Because the composition of the middle crust cannot be well constrained by the above data set, the data set published by Rudnick & Fountain (1995) is used for comparison. It indicated the composition of the middle crust is granulite facies and might be pelitic gneisses.Granulite facies used to be interpreted as residues of partial melting, which coincidences with the previous study on partial melting middle crust. Amphibolite facies are thought to be produced after delamination, when underplating works in the rebound of the lower crust and lithospheric mantle. From the seismology study, I have made several followed conclusions: 1) Through the numerical simulation experiment of surface wave propagating in heterogeneity media, we can find that amplitude and polarization of surface wave only change a little when considering heterogeneity. Furthermore, it is proved that QL waves, generated by surface wave scattering, are caused by lateral variation of anisotropy but not by heterogeneity. 2) QL waves are utilized to determine the variation of uppermost mantle anisotropy of the Tibetan plateau. QL waves are identified from the seismograms of the selected paths recorded by the CAD station. The location of azimuth anisotropy gradient is estimated from the group velocities of Rayleigh wave, Love wave and QL wave. It suggests that south-north lateral variation of azimuthal anisotropy locates in Tanggula mountain, and east-west lateral variation in the north of Gandese mountain with 85°E longitude and near the Jinsha river fault with 85°E longitude.

Millstone Hill电离层F层等效风场的气候学研究

Neutral winds and electric fields in the ionospheric F layer play important roles in the variations of the ionosphere, and also affect the thermospheric circulation via the close coupling between the ionosphere and the thermosphere. By now, the neutral winds and electric drifts are generally observed with ground-based Fabry-Perot interferometers (FPI) and incoherent scatter radars (ISR), rockets, and satellite-borne instrument. Based on the servo theory, the ionospheric equivalent winds, which include the information of both the neutral winds and electric fields, can be derived from these characteristic parameters observed by ionosondes. This indirect derivation has potential values in climatological researches and space weather forecast. With the data set of the incoherent scatter radar observations at Millstone Hill, USA, from 1976 to 2006, we statistically analyzed the climatological variations of the vertical component of the equivalent winds (VEWs) over Millstone Hill, which are derived from the ionospheric key parameters (the peak electron number density and peak height of the F2 layer, NmF2 and hmF2) on the basis of the servo theory, Liu's method, and measurements from the ion line-of-sight velocity as well. The main results of this analysis are summarized as follows: (1) The values of VEWs over Millstone Hill during nighttime are stronger than in the daytime, and the upward drift dominates most of the day. In 1993, Hagan found that the component of the neutral winds in the magnetic meridion in daytime is weaker than during nighttime under both solar maximum and minimum conditions; he also found that the equatorward winds dominate most of the day. Both results suggest that the thermosphere in Millstone Hill is modulated by the aurorally driven high-latitude circulation cell; that is, during geomagnetic quiet periods, the average auroral activity is strong enough to drive thermospheric circulation equatorward for most of the day at Millstone Hill. Moreover, since ion drag is the strongest during daytime when F region densities are enhanced by photoionization, the wind speeds are smaller during the daytime than in the nighttime. (2) There is equinoctial symmetry in VEWs at Millstone Hill. The amplitudes and phases of VEWs in spring are quite similar to those in autumn. In contrast, the nighttime upward drift in winter is weaker than in summer and the difference becomes more significant with increasing solar activity. This solstice asymmetry indicates that, the aurorally driven circulation in the northern hemisphere at Millstone Hill latitude is weaker in winter due to arctic darkness, because the subsolar point is in the southern hemisphere. (3) The comparison of the VEWs derived from three methods, i.e., the servo theory, Liu's method, and the ISR ion line-of-sight velocity measurements, indicates that the amplitudes and main phase tendencies of these VEWs accord well with each other during nighttime hours. However, the case in the daytime is relatively worse. This daytime discrepancy can be explained in terms of the effects of photochemical processes and the choices of the servo constants. A larger servo constant gives a stronger plasma drift in daytime. Therefore, this study tells how important to choose a suitable constant for deriving VEWs at Millstone Hill.

地质体科学计算可视化研究及其应用

Describing visually space-time properties of geological phenomena consists of one of the most important parts in geology research. Such visual images are of usually helpful for analyzing geological phenomena and for discovering the regulations behind geological phenomena. This report studies mainly three application problems of scientific visualization in geology: (Dvisualizing geological body A new geometric modeling technique with trimmed surface patches has been eveloped to visualize geological body. Constructional surfaces are represented as trimmed surfaces and a constructional solid is represented by the upper and lower surface composed of trimmed surface patches from constructional surfaces. The technique can completely and definitely represent the structure of geological body. It has been applied in visualization for the coal deposit in Huolinhe, the aquifer thermal energy storage in Tianjin and the structure of meteorite impact in Cangshan et al. (2)visualizing geological space field Efficient visualization methods have been discussed. Marching-Cube algorithm used has been improved and is used to extract iso~surface from 3D data set, iso-line from 2D data set and iso-point from ID data set. The improved method has been used to visualize distribution and evolution of the abnormal pressures in Zhungaer Basin. (3)visualizing porous space a novel way was proposed to define distance from any point to a convex set. Thus a convex set skeleton-based implicit surface modeling technique is developed and used to construct a simplified porous space model. A Buoyancy Percolation numerical simulation platform has been developed to simulate the process of migration of oil in the porous media saturated with water.

共反射面元叠加

The seismic survey is the most effective prospecting geophysical method during exploration and development of oil/gas. The structure and the lithology of the geological body become increasingly complex now. So it must assure that the seismic section own upper resolution if we need accurately describe the targets. High signal/noise ratio is the precondition of high-resolution. As one important seismic data processing method, Stacking is an effective means to suppress the records noise. Broadening area of surface stacked is more important to enhance genuine reflection signals and suppressing unwanted energy in the form of coherent and random ambient noise. Common reflection surface stack is a macro-model independent seismic imaging method. Based on the similarity of CRP trace gathers in one coherent zone, CRS stack effectively improves S/N ratio by using more CMP trace gathers to stack. It is regarded as one important method of seismic data processing. Performing CRS stack depends on three attributes. However, the equation of CRS is invalid under condition of great offset. In this thesis, one method based on velocity model in depth domain is put forward. Ray tracing is used to determine the traveltime of CRP in one common reflection surface by the least squares method to regress the equation of CRS. Then we stack in the coherent seismic data set according to the traveltime, and get the zero offset section. In the end of flowchart of implementing CRS stack, one method using the dip angle to enhance the ratio of S/N is used. Application of the method on synthetic examples and field seismic records, the results of this method show an excellent performance of the algorithm both in accuracy and efficiency.

双聚焦偏移速度估计与可分表示叠前弹性反演

In exploration seismology, the geologic target of oil and gas reservoir in complex medium request the high accuracy image of the structure and lithology of the medium. So the study of the prestack image and the elastic inversion of seismic wave in the complex medium come to the leading edge. The seismic response measured at the surface carries two fundamental pieces of information: the propagation effects of the medium and the reflections from the different layer boundaries in the medium. The propagation represent the low-wavenumber component of the medium, it is so-called the trend or macro layering, whereas the reflections represent the high-wavenumber component of the medium, it is called the detailed or fine layering. The result of migration velocity analysis is the resolution of the low-wavenumber component of the medium, but the prestack elastic inversion provided the resolution of the high-wavvenumber component the medium. In the dissertation, the two aspects about the migration velocity estimation and the elastic inversion have been studied.Firstly, any migration velocity analysis methods must include two basic elements: the criterion that tell us how to know whether the model parameters are correct and the updating that tell us how to update the model parameters when they are incorrect, which are effected on the properties and efficiency of the velocity estimation method. In the dissertation, a migration velocity analysis method based on the CFP technology has been presented in which the strategy of the top-down layer stripping approach are adapted to avoid the difficult of the selecting reduce .The proposed method has a advantage that the travel time errors obtained from the DTS panel are defined directly in time which is the difference with the method based on common image gather in which the residual curvature measured in depth should be converted to travel time errors.In the proposed migration velocity analysis method, the four aspects have been improved as follow:? The new parameterization of velocity model is provided in which the boundaries of layers are interpolated with the cubic spline of the control location and the velocity with a layer may change along with lateral position but the value is calculated as a segmented linear function of the velocity of the lateral control points. The proposed parameterization is suitable to updating procedure.? The analytical formulas to represent the travel time errors and the model parameters updates in the t-p domain are derived under local lateral homogeneous. The velocity estimations are iteratively computed as parametric inversion. The zero differential time shift in the DTS panel for each layer show the convergence of the velocity estimation.? The method of building initial model using the priori information is provided to improve the efficiency of velocity analysis. In the proposed method, Picking interesting events in the stacked section to define the boundaries of the layers and the results of conventional velocity analysis are used to define the velocity value of the layers? An interactive integrate software environment with the migration velocity analysis and prestack migration is built.The proposed method is firstly used to the synthetic data. The results of velocity estimation show both properties and efficiency of the velocity estimation are very good.The proposed method is also used to the field data which is the marine data set. In this example, the prestack and poststack depth migration of the data are completed using the different velocity models built with different method. The comparison between them shows that the model from the proposed method is better and improves obviously the quality of migration.In terms of the theoretical method of expressing a multi-variable function by products of single-variable functions which is suggested by Song Jian (2001), the separable expression of one-way wave operator has been studied. A optimization approximation with separable expression of the one-way wave operator is presented which easily deal with the lateral change of velocity in space and wave number domain respectively and has good approach accuracy. A new prestack depth migration algorithm based on the optimization approximation separable expression is developed and used to testing the results of velocity estimation.Secondly, according to the theory of the seismic wave reflection and transmission, the change of the amplitude via the incident angle is related to the elasticity of medium in the subsurface two-side. In the conventional inversion with poststack datum, only the information of the reflection operator at the zero incident angles can be used. If the more robust resolutions are requested, the amplitudes of all incident angles should be used.A natural separable expression of the reflection/transmission operator is represented, which is the sum of the products of two group functions. One group function vary with phase space whereas other group function is related to elastic parameters of the medium and geological structure.By employing the natural separable expression of the reflection/transmission operator, the method of seismic wave modeling with the one-way wave equation is developed to model the primary reflected waves, it is adapt to a certain extent heterogeneous media and confirms the accuracy of AVA of the reflections when the incident angle is less than 45'. The computational efficiency of the scheme is greatly high.The natural separable expression of the reflection/transmission operator is also used to construct prestack elastic inversion algorithm. Being different from the AVO analysis and inversion in which the angle gathers formed during the prstack migration are used, the proposed algorithm construct a linear equations during the prestack migration by the separable expression of the reflection/transmission operator. The unknowns of the linear equations are related to the elasticity of the medium, so the resolutions of them provided the elastic information of the medium.The proposed method of inversion is the same as AVO inversion in , the difference between them is only the method processing the amplitude via the incident angle and computational domain.