岩石中地震波速度和衰减的应力变化响应研究

Stress change is one of key factors in seismic nucleating and triggering; therefore for understanding and forecasting earthquakes, it is necessary to research on stress status and its changes in rocks. Propagating in underground structures, wave velocity and attenuation contain information on stress changes of the Earth’s interior. For a better understanding of relationship between seismic data and stress changes, modeling and ultrasonic test supply significant references. In this article, acoustoelastic theory is introduced to explain nonlinear elastic characteristics of rocks. Based on the acoustoelastic theory, a solid-fluid coupled model is given to calculate velocity under different stress for porous and liquid fulfilled rocks. Except for the stress-velocity relationship, effects of pore pressure induced stress changes on ultrasonic coda attenuation are also studied. Intrinsic attenuation quality factors are calculated for a comparison purpose. Finally, the relationship between elastic constants and stress changes is thoroughly investigated, a mixture model from two phases of Hooke media is introduced to explain the differences between dynamic and static moduli, a relation among wave length, wave velocities and elastic moduli considering dimension of microstructure, dimension and state of surface between phases is presented. The most important aspect of this work is exploring and establishing relationships between the seismic properties of rocks and changes of their stress conditions, which will have its application in earthquake forecast and seismic hazard.

大型反倾岩体变形破坏机制及稳定性分析———以金沙江宽谷坝址龙蟠边坡为例

A large number of catastrophic accidents were aroused by the instability and destruction of anti-dip rock masses in the worldwide engineering projects, such as hydropower station, mine, railways and so on. Problems in relation to deformation and failure about anti-dip rock slopes are significant for engineering geology research. This dissertation takes the Longpan slope in the Jinsha River as a case to study the deformation mechanism of large-scale anti-dip rock masses and the slope stability analysis method. The primary conclusions are as follows. The Dale Reach of Jinsha River, from Longpan to the debouchment of Chongjiang tributary, is located in the southeastern margin of the Qinghai-Tibet Plateau. Longpan slope is the right embankment of Dale dam, it is only 26 km to the Shigu and 18 km to Tiger Leaping Gorge. The areal geology tectonic structures here area are complicated and blurry. Base on the information of geophysical exploration (CSAMT and seismology) and engineering geological investigation, the perdue tectonic pattern of Dale Reach is put forward for the first time in this paper. Due to the reverse slip of Longpan fault and normal left-rotation of Baihanchang fault, the old faulted valley came into being. The thick riverbed sediments have layered characters of different components and corresponding causes, which attribute to the sedimentary environments according with the new tectonic movements such as periodic mountain uplifting in middle Pleistocene. Longpan slope consists of anti-dip alternate sandstone and slate stratums, and the deformable volume is 6.5×107m3 approximately. It was taken for an ancient landslide or toppling failure in the past so that Dale dam became a vexed question. Through the latest field surveying, displacement monitoring and rock masses deforming characters analyses, the geological mechanism is actually a deep-seated gravitational bending deformation. And then the discrete element method is used to simulate the deforming evolution process, the conclusion accords very well with the geo-mechanical patterns analyses. In addition strength reduction method based on DEM is introduced to evaluate the factor of safety of anti-dip rock slope, and in accordance with the expansion way of the shear yielding zones, the progressive shear failure mechanism of large-scale anti-dip rock masses is proposed for the first time. As an embankment or a close reservoir bank to the lower dam, the stability of Longpan slope especially whether or not resulting in sliding with high velocity and activating water waves is a key question for engineering design. In fact it is difficult to decide the unified slip surface of anti-dip rock slope for traditional methods. The author takes the shear yielding zones acquired form the discrete element strength reduction calculation as the potential sliding surface and then evaluates the change of excess pore pressure and factor of stability of the slope generated by rapid drawdown of ponded water. At the same time the dynamic response of the slope under seismic loading is simulated through DEM numerical modeling, the following results are obtained. Firstly the effective effect of seismic inertia force is resulting in accumulation of shear stresses. Secondly the discontinuous structures are crucial to wave transmission. Thirdly the ultimate dynamic response of slope system takes place at the initial period of seismic loading. Lastly but essentially the effect of earthquake load to bringing on deformation and failure of rock slope is the coupling effect of shear stresses and excess pore water pressure accumulation. In view of limitations in searching the critical slip surface of rock slope of the existing domestic and international software for limit equilibrium slope stability analyses, this article proposes a new method named GA-Sarma Algorithm for rock slope stability analyses. Just as its name implies, GA-Sarma Algorithm bases on Genetic Algorithm and Sarma method. GA-Sarma Algorithm assumes the morphology of slip surface to be a broken line with traceability to extend along the discontinuous surface structures, and the slice boundaries is consistent with rock mass discontinuities such as rock layers, faults, cracks, and so on. GA-Sarma Algorithm is revolutionary method that is suitable for global optimization of the critical slip surface for rock slopes. The topics and contents including in this dissertation are closely related to the difficulties in practice, the main conclusions have been authorized by the engineering design institute. The research work is very meaningful and useful for the engineering construction of Longpan hydropower station.

中高层大气对低层大气声重波响应的分析

Acoustic Gravity waves (AGW) play an important role in balancing the atmospheric energy and momentum budget. Propagation of gravity wave in the atmosphere is one of the important factors of changing middle and upper atmosphere and ionosphere. The purpose of this dissertation is to study the propagation of gravity wave in a compression atmosphere whit means of numerical simulation and to analyze the response of middle and upper atmosphere to pulse disturbance from lower atmosphere. This work begins with the establishment of 2-D fully nonlinear compressible atmospheric dynamic model in polar coordinate, which is used ton numerically study gravity wave propagation. Then the propagation characteristics of acoustic gravity wave packets are investigated and discussed. We also simulate the response of middle and upper atmosphere to pulse disturbance of lower atmosphere in background winds or without background winds by using this model and analyze the data we obtained by using Fourier Transform (FT), Short-time Fourier Transform (STFT) and Empirical Mode Decomposition (EMD) method which is an important part of Hilbert-Huang Transform (HHT). The research content is summarized in the following: 1. By using a two-dimensional full-implicit-continuous-Eulerian (FICE) scheme and taking the atmospheric basic motion equations as the governing equations, a numerical model for nonlinear propagation of acoustic gravity wave disturbance in two-dimensional polar coordinates is solved. 2. Then the propagation characteristics of acoustic gravity wave packets are investigated and discussed. Results of numerical simulation show that the acoustic gravity wave packets propagate steadily upward and keep its shape well after several periods. 3. We simulate the response of middle and upper atmosphere to pulse disturbance of lower atmosphere in background winds or without background winds by using this model, and obtain the distribution of a certain physical quantity in time and space from earth’s surface to 300km above. The results reveal that the response of ionosphere occurs at a large horizontal distance from the source and the disturbance becomes greater with increasing of height. The situation when the direction of the background wind is opposite to or the same as the direction of disturbed velocity of gravity-wave is studied. The results show that gravity wave propagating against winds is easier than those propagating along winds and the background wind can accelerate gravity wave propagation. Just upon the source, an acoustic wave component with period of 6 min can be found. These images of simulation are similar to observations of the total electron content (TEC) disturbances caused by the great Sumatra-Andaman earthquake on December 26 in 2004. 4. Using the EMD method the disturbed velocity data of a certain physical quantity in time and space can be decomposed into a series of intrinsic mode function (IMF) and a trend mode respectively. The results of EMD reveal impact of the gravity wave frequency under the background winds.

中国华北和美国加州地区地震层析成像研究

In recent years seismic tomography has become a powerful tool for studying the three-dimensional crust and mantle structure. In this study, we collected a large number of regional and teleseismic travel-time data and used seismic tomography method to study the relationship between earthquake occurrence and crustal heterogeneity for the 1992 Landers earthquake, heterogeneity and evolution of lithosphere under North China Craton and Southern California, and deep structure and origin of the Changbai intraplate volcano in Northeast China. Our results show a correlation between the seismic rupture zone and crustal heterogeneity. The distribution of the Landers aftershocks is cluster-like and separated or terminated in areas where low-velocity anomalies exist．Most of the large earthquakes with magnitudes >4.0 occurred in or around areas with high P-wave velocity．The possibility is that high-velocity areas are brittle and strong parts which can sustain seismogenic stress，and so can generate earthquakes. Our tomographic images show a very heterogeneous structure in the crust and upper mantle beneath Southern California. Three major anomalies in the upper mantle are revealed clearly beneath the southern Sierra Nevada, Transverse Ranges and Salton Trough. We consider that the high-velocity anomaly beneath the Transverse Ranges was formed through asymmetrical two-side convergence of subcrustal lithosphere and sinking to asthenosphere. Formation of the dense crust root and “drip structure” caused the high-velocity anomaly under the southern Sierra Nevada. The Salton Trough low is the response to the lithospheric extension when the Pacific plate was rifted away from the North American Plate. The tomograpic images beneath the North China Craton show that there exist different lithospheric structures under the different blocks. Complex, prominent low-velocity and high-velocity anomalies are imaged beneath the North China Basin, Trans-North China Orogen (TNCO), and Ordos Block which correspond to rifted, orogenic and cratonic lithospheres, respectively. The thickness of the three-type lithospheres is about 70, 90 and >250 km, respectively. Our results suggest that lithospheric thinning under the eastern part of North China Craton is due to long-term replacement and chemical and thermal erosion of the ancient lithosphere by the hot asthenosphere. The remains of ancient lithosphere exist either in the present upper mantle or have sunk into the mantle transition zone. Our tomographic result of the Changbai volcanic area suggests that the origin of the Changbai volcano is related to the deep dehydration of the subducted Pacific slab and corner flow in the big mantle wedge (BMW) above the stagnant Pacific slab.

地震P-S波时差耦合作用的斜坡崩滑效应研究

China locates between the circum-Pacific and the Mediterranean-Himalayan seismic belt. The seismic activities in our country are very frequent and so are the collapses and slides of slope triggered by earthquakes. Many collapses and slides of slope take place mainly in the west of China with many earthquakes and mountains, especially in Sichuan and Yunnan Provinces. When a strong earthquake happening, the damage especially in mountains area caused by geological hazards it triggered such as rock collapses, landslides and debris flows is heavier than that it caused directly. A conclusion which the number of lives lost caused by geological hazards triggered by a strong earthquake in mountains area often accounts for a half even more of the total one induced by the strong earthquake can be made by consulting the statistical loss of several representative earthquakes. As a result, geological hazards such as collapses and slides of slope triggered by strong earthquakes attract wide attention for their great costs. Based on field geological investigation, engineering geological exploration and material data analysis, chief conclusions have been drawn after systematic research on formation mechanism, key inducing factors, dynamic characteristics of geological hazards such as collapses and slides of slope triggered by strong earthquakes by means of engineering geomechanics comprehensive analysis, finite difference numerical simulation test, in-lab dynamic triaxial shear test of rock, discrete element numerical simulation. Based on research on a great number of collapses and landslides triggered by Wenchuan and Xiaonanhai Earthquake, two-set methods, i.e. the method for original topography recovering based on factors such as lithology and elevation comparing and the method for reconstructing collapsing and sliding process of slope based on characteristics of seism tectonic zone, structural fissure, diameter spatial distribution of slope debris mass, propagation direction and mechanical property of seismic wave, have been gotten. What is more, types, formation mechanism and dynamic characteristics of collapses and slides of slope induced by strong earthquakes are discussed comprehensively. Firstly, collapsed and slided accumulative mass is in a state of heavily even more broken. Secondly, dynamic process of slope collapsing and sliding consists of almost four stages, i.e. broken, thrown, crushed and river blocked. Thirdly, classified according to failure forms, there are usually four types which are made up of collapsing, land sliding, land sliding-debris flowing and vibrating liquefaction. Finally, as for key inducing factors in slope collapsing and sliding, they often include characteristics of seism tectonic belts, structure and construction of rock mass, terrain and physiognomy, weathering degree of rock mass and mechanical functions of seismic waves. Based on microscopic study on initial fracturing of slope caused by seismic effect, combined with two change trends which include ratio of vertical vs. horizontal peak ground acceleration corresponding to epicentral distance and enlarging effect of peak ground acceleration along slope, key inducing factor of initial slope fracturing in various area with different epicentral distance is obtained. In near-field area, i.e. epicentral distance being less than 30 km, tensile strength of rock mass is a key intrinsic factor inducing initial fracturing of slope undergoing seismic effect whereas shear strength of rock mass is the one when epicentral distance is more than 30 km. In the latter circumstance, research by means of finite difference numerical simulation test and in-lab dynamic triaxial shear test of rock shows that initial fracture begins always in the place of slope shoulder. The fact that fracture strain and shear strength which are proportional to buried depth of rock mass in the place of slope shoulder are less than other place and peak ground acceleration is enlarged in the place causes prior failure at slope shoulder. Key extrinsic factors inducing dynamic fracture of slope at different distances to epicenter have been obtained through discrete element numerical simulation on the total process of collapsing and sliding of slope triggered by Wenchuan Earthquake. Research shows that combined action of P and S seismic waves is the key factor inducing collapsing and sliding of slope at a distance less than 64 km to initial epicenter along earthquake-triggering structure. What is more, vertical tensile action of P seismic wave plays a leading role near epicenter, whereas vertical shear action of S seismic wave plays a leading role gradually with epicentral distance increasing in this range. On the other hand, single action of P seismic wave becomes the key factor inducing collapsing and sliding of slope at a distance between 64 km and 216 km to initial epicenter. Horizontal tensile action of P seismic wave becomes the key factor gradually from combined action between vertical and horizontal tensile action of P seismic wave with epicentral distance increasing in this distance range. In addition, initial failure triggered by strong earthquakes begins almost in the place of slope shoulder. However, initial failure beginning from toe of slope relates probably with gradient and rock occurrence. Finally, starting time of initial failure in slope increases usually with epicentral distance. It is perhaps that the starting time increasing is a result of attenuating of seismic wave from epicenter along earthquake-triggering structure. It is of great theoretical and practical significance for us to construct towns and infrastructure in fragile geological environment along seism tectonic belts and conduct risk management on earthquake-triggered geological hazards by referring to above conclusions.

特大地震激发地球自由振荡的数值模拟研究

Large earthquakes, such as the Chile earthquake in 1960 and the Sumatra-Andaman earthquake on Dec 26, 2004 in Indonesia, have generated the Earth’s free oscillations. The eigenfrequencies of the Earth’s free oscillations are closely related to the Earth’s internal structures. The conventional methods, which mainly focus on calculating the eigenfrequecies by analytical ways, and the analysis on observations can not easily study the whole processes from earthquake occurrence to the Earth’s free oscillation inspired. Therefore, we try to use numerical method incorporated with large-scale parallel computing to study on the Earth’s free oscillations excited by giant earthquakes. We first give a review of researches and developments of the Earth’s free oscillation, and basical theories under spherical coordinate system. We then give a review of the numerical simulation of seismic wave propagation and basical theories of spectral element method to simulate global seismic wave propagation. As a first step to study the Earth’s free oscillations, we use a finite element method to simulate the propagation of elastic waves and the generation of oscillations of the chime bell of Marquis Yi of Zeng, by striking different parts of the bell, which possesses the oval crosssection. The bronze chime bells of Marquis Yi of Zeng are precious cultural relics of China. The bells have a two-tone acoustic characteristic, i.e., striking different parts of the bell generates different tones. By analysis of the vibration in the bell and the spectrum analysis, we further help the understanding of the mechanism of two-tone acoustic characteristics of the chime bell of Marquis Yi of Zeng. The preliminary calculations have clearly shown that two different modes of oscillation can be generated by striking different parts of the bell, and indicate that finite element numerical simulation of the processes of wave propagation and two-tone generation of the chime bell of Marquis Yi of Zeng is feasible. These analyses provide a new quantitative and visual way to explain the mystery of the two-tone acoustic characteristics. The method suggested by this study can be applied to simulate free oscillations excited by great earthquakes with complex Earth structure. Taking into account of such large-scale structure of the Earth, small-scale low-precision numerical simulation can not simply meet the requirement. The increasing capacity in high-performance parallel computing and progress on fully numerical solutions for seismic wave fields in realistic three-dimensional spherical models, Spectral element method and high-performance parallel computing were incorporated to simulate the seismic wave propagation processes in the Earth’s interior, without the effects of the Earth’s gravitational potential. The numerical simulation shows that, the results of the toroidal modes of our calculation agree well with the theoretical values, although the accuracy of our results is much limited, the calculated peaks are little distorted due to three-dimensional effects. There exist much great differences between our calculated values of spheroidal modes and theoretical values, because we don’t consider the effect the Earth’ gravitation in numerical model, which leads our values are smaller than the theoretical values. When , is much smaller, the effect of the Earth’s gravitation make the periods of spheroidal modes become shorter. However, we now can not consider effects of the Earth’s gravitational potential into the numerical model to simulate the spheroidal oscillations, but those results still demonstrate that, the numerical simulation of the Earth’s free oscillation is very feasible. We make the numerical simulation on processes of the Earth’s free oscillations under spherically symmetric Earth model using different special source mechanisms. The results quantitatively show that Earth’s free oscillations excited by different earthquakes are different, and oscillations at different locations are different for free oscillation excited by the same earthquake. We also explore how the Earth’s medium attenuation will take effects on the Earth’s free oscillations, and take comparisons with the observations. The medium attenuation can make influences on the Earth’s free oscillations, though the effects on lower-frequency fundamental oscillations are weak. At last, taking 2008 Wenchuan earthquake for example, we employ spectral element method incorporated with large-scale parallel computing technology to investigate the characteristics of seismic wave propagation excited by Wenchuan earthquake. We calculate synthetic seismograms with one-point source model and three-point source model respectively. Full 3-D visualization of the numerical results displays the profile of the seismic wave propagation with respect to time. The three-point source, which was proposed by the latest investigations through field observation and reverse estimation, can better demonstrate the spatial and temporal characteristics of the source rupture processes than one-point source. Primary results show that those synthetic signals calculated from three-point source agree well with the observations. This can further reveal that the source rupturing process of Wenchuan earthquake is a multi-rupture process, which is composed by at least three or more stages of rupture processes. In conclusion, the numerical simulation can not only solve some problems concluding the Earth’s ellipticity and anisotropy, which can be easily solved by conventional methods, but also finally solve the problems concluding topography model and lateral heterogeneity. We will try to find a way to fully implement self-gravitation in spectral element method in future, and do our best to continue researching the Earth’s free oscillations using the numerical simulations to see how the Earth’ lateral heterogeneous will affect the Earth’s free oscillations. These will make it possible to bring modal spectral data increasingly to bear on furthering our understanding of the Earth’s three-dimensional structure.

活动构造区区域地壳稳定性研究——以金沙江水电梯级工程规划区为例

The study of regional crustal stability of active tectonic region basically includes analysis of recent activity of Earth's crust, single factor assessment, study of complexity, and comprehensive assessment of crust stability. In this thesis, some work are made as follows: · Based on abundant data from gravity field, aeromagnetic survey, magnetism, magnetotelluric deep sounding, remote sensing and geotectonic as well as earthquakes observed in recent years around this region and adjacent zones, we can get a through understanding about the structural features and activity of the earth's crust in Chuan-Dian region. The results from explosion earthquake and telluric electromagnetic sounding are consistent with the structural features of the crust manifested by the geophysical field. The data of deep geologic structures are important for us to work out a vivid three-dimensional model of the earth's crustal structure of the Jinsha River region. According to a synthesis, the author of this thesis proposes some indicators for dividing the faulted blocks. It can also be inferred that the movement of the Chuan-Dian faulted block, which is the relatively active part of southwestern China, is controlled by the boundary faults, and the intensive activity and deformation are concentrated along the boundaries of the block. · Mainly discussing respectively the mechanism and laws of active faults, earthquakes, and geological hazards activity, and their influences on the stability and security of engineering, also trying to probe into the way to assess the risk of single factor in this section. Especially with the method of fractal geometry, the thesis has discussed how to study the complexity of each factor. These geologic hazards which are distributed at the uppermost part of the crust in this region form a typical mountainous set of the active tectonic areas. The results of survey show that some slopes are liable- to -sliding with a weak layer of low shear strength. Occurrences of landslides are to a great extent related to local geological structures, in particular active faults. This is why numerous landslides have occurred simultaneously around the epicenter of a strong earthquake or the center of a strong rainfall, which are related to active faults. · The analysis of the crustal stability is based on a regional grid division, and a fuzzy comprehensive analysis method is used to determine the grade of the quality in each grid. The evaluation factors and their weights are taken from the results of the hierarchical analysis. The evaluation indexes consist of qualitative and quantitative ones. The qualitative ones can be quantified through the experts weighing system, while the quantitative ones can be obtained from statistical analysis. For quality grades, four levels are used: stable, essentially stable, sub-stable, and unstable. The results of the evaluation on Jinshajiang region demonstrate that the crustal stability become distinctly worse in the areas controlled by active deep faults. Therefore, detailed investigations on the active faulting and geologic hazards, include earthquake activity are especially necessary for those areas adjacent to the deep fault belts. On the bases of the data available and the survey results, we have made a preliminary assessment for the construction conditions and adaptability of every planned site in the middle or lower reaches of Jinsha River. Finally, the thesis prospected the vista of the study of crustal stability.

宣龙式赤铁矿含矿岩系的成矿过程研究

Xuanlong-type Hematite Deposits, distributed in Xuanhua and Longguang area in Hebei province and hosted in the Changchengian Chuanlinggou Formation of Mesoproterozoic, is an oldest depositional iron deposit characterized by oolitic and stromatolitic hematite and siderite. This thesis made an systematic study of its sedimentary, sedimentology, geochemistry, mineralogy and sequence stratigraphy. Based on above, the mechanism and background of biomineralization are discussed. There are four types of hematite ores including stromatolite, algal oolite, algal pisolite and oncolite. Based on detailed study on ore texture, the authors think both algal oolite and algal pisolite ores are organic texture ores, and related to the role of microorganisms. The process of blue-green algae and bacteria in the Xuanlong basin absorbing, adsorbing and sticking iron to build up stromatolite is the formation process of Xuanlong-type hematite deposit. Researches on ore-bearing series and ore geochemistry show that the enrichment of elements is closely related to the microorganism activities. Fe_2O_3 is enriched in dark laminations of stromatolite with much organic matter and SiO_2 in light laminations with detrital matters. The trace elements, especially biogenic elements, including V, P, Mo are enriched in ores but relatively low in country rocks. The paper also demonstrates on the sequence stratigraphy of hematite deposits and five sequences and twelve systems are divided. The characteristics of sequence stratigraphy show that the deposit-forming location has obviously selectivity and always exists under a transgressive setting. The oxygen isotope in hematite is about -2.2～5.7‰, which is similar to that of Hamlys iron formation of Australia but more negative than that of volcanic or hydrothermal iron deposits characterized by high positive values. The calculation by the result of oxygen isotope analysis shows that the temperature of ancient sea water was 48.53℃. The negative value of carbon isotope from siderite indicates its biogenic carbon source. Meanwhile, the occurrence of seismite in the ore-beds, which indicates the formation of hematite deposits is associated with frequent shock caused by structural movement such as distal volcano or ocean-bottom earthquake etc, show the occurrence of hematite deposits is eventual, not gradual. In shorts, Xuanlong-type hematite deposits were the result of interaction among geological setting of semi-isolated Xuanglong basin, favorable hot and humid climate condition, abundant iron source, microorganism such as algae and bateria as well as the fluctuation of the sea level.

三维非均匀各向异性介质中的纵波走时反演研究

Many observations show that seismic anisotropy is very common in the crust and upper mantle of the Earth. Seismic anisotropy can provide some clue about the changing and transporting process inside the earth. in recent years, abundant earthquake travel time data are accumulated, computers become more powerful, and these make the inversion of earthquake travel time data practical. In this thesis we studied the theory of elastic wave in anisotropic media, some formule for travel time inversion were derived. We present an iterative procedure to determine 21 elastic parameters from qP wave travel times. No a priori assumptions about heterogeneity and anisotropy of the model are made. The procedure is suitable for the case when we know nothing about the symmetry of anisotropy of the media, as well as for the case of earthquake travel time inversion which may contain various symmetry of anisotropy. The procedure is tested with a synthetic multiple-source offset VSP experiment. The results proved that the formulae are correct, and the procedure is practical. The results and the related theory indicate that the anisotropic inversion needs more rays than isotropic case. For a 2-D weak anisotropic (WA) medium, we need at least 5 rays in different directions to retrieve the elastic parameters on one grid point, and for a 3-D WA medium we need at least 15 rays in different directions to retrieve the elastic parameters on one grid point. The results also indicate that the starting background velocity has no influence on the final results, at least for the model we specified. Our results also show that insufficient illumination coverage will slow down the convergence rate, and make the results more sensitive to noise. We apply the procedure to a set of field travel time data. The data is from an artificial seismic observation. This observation is for locating micro-seismic events around a tunnel, its purpose is to find out if the digging process and the stress condition around the tunnel can generate micro-cracks. The size of this area is around 100m. The anisotropy derived from qP travel times is the same as the anisotropy showed by apparent velocities, and is also consistent with the anisotropy derived from S-wave splitting phenomena.

云南岩石圈流变学及多震层孕震环境

The Study on rheology of the lithosphere and the environments of the seismogenic layer is currently the basic project of the international earthquake research. Yunnan is the ideal place for studying this project. Through the multi-disciplinary comprehensive study of petrology, geophysics, seismo-geology, rock mechanics, etc., the depth-strength profiles of the lithosphere have been firstly constructed, and the seismogenic layer and its geophysical and tectonic environments in Yunnan have been systematically expounded in this paper. The related results achieved are of the important significances for further understanding the mechanism of strong earthquake generation, dividing the potential foci and exposing recent geodynamical processes in Yunnan. Through the comprehensive contrast of the metamorphic rocks in early and middle Proterozoic outcropping on the surface, DSS data and experimental data of rock seismic velocity under high temperature and high pressure, the petrological structure of the crust and upper mantle has been studied on Yunnan: the upper, middle and lower crust is composed of the metamorphic rocks of greenschist, amphibolite and granulite facies, respectively or granitoids, diorites and gabbros, respectively, and the upper mantle composed of the peridotites. Through the contrast studies of the heat flow and epicenters of the strong earthquakes, the distribution of the geotemperature and the data of focal depth, the relationship of between seismicity and geothermal structure of the lithosphere in Yunnan has been studied: the strong earthquakes with magnitude M ≥ 6.0 mainly take place at the geothermal gradient zone, and the seismic foci densely distribute between 200～500 ℃ isogeotherms. On the basis of studies of the rock properties and constituents of the crust and upper mantle and geothermal structure of the lithosphere, the structure of the rheological stratification of the lithosphere has been studied, and the corresponding depth-strength profiles have been constructed in Yunnan. The lithosphere in majority region of Yunnan has the structure of the rheological stratification, i.e. the brittle regime in the upper crust or upper part of the upper crust, ductile regime in the middle crust or lower part of the upper crust to middle crust, ductile regime in the lower crust and ductile regime in the subcrustal lithosphere. The rheological stratification has the quite marked lateral variations in the various tectonic units. The distributions of the seismogenic layer have been determined by using the high accurate data of focal depth. Through the contrast of the petrological structure, the structure of seismic velocity, electric structure, geotemperature structure, and rheological structure and the study of the focal mechanism in the seismogenic layer, the geophysical environments of the seismogenic layer in Yunnan have been studied. The seismogenic layer in Yunnan is located at the depths of 3 ～ 20 km; the rocks in the seismogenic layer are composed of the metamorphic rocks of greenschist to amphibolite facies (or granites to diorites); the seismogenic layer and its internal focal regions of strong earthquakes have the structure of medium properties with the relatively high seismic velocity, high density and high resistivity; there exists the intracrustal low seismic velocity and high conductivity layer bellow the seismogenic layer, the geotemperature is generally 100～500 ℃ in the depth range in which the seismogenic layer is located. The horizontal stress field predominates in the seismogenic layer, the seismogenic layer corresponds to the brittle regime of the upper crust or brittle regime of the upper crust to semibrittle regime of the middle crust. The formation of the seismogenic layer, preparedness and occurrence of the strong earthquakes is the result of the comprehensive actions of the source fault, rock constituent, structure of the medium properties, distribution of the geotemperature, rheological structure of the seismogenic layer and its external environments. Through the study of the structure, active nature, slip rate, segmentation of the active faults, and seismogenic faults, the tectonic environments of the seismogenic layer in Yunnan have been studied. The source faults of the seismogenic layer in Yunnan are mainly A-type ones and embody mainly the strike slip faults with high dip angle. the source faults are the right-lateral strike slip ones with NW-NNW trend and left-lateral strike slip ones with NE-NEE trend in Southwestern Yunnan, the right-lateral strike slip ones with NNW trend and left-lateral strike slip ones with NNE trend (partially normal ones) in Northwestern Yunnan, the right-lateral strike slip ones with NWW trend in Central Yunnan and left-lateral strike slip ones with NW-NNW trend in Eastern Yunnan. Taking Lijiang earthquake with Ms = 7.0 for example. The generating environments of the strong earthquake and seismogenic mechanical mechanism have been studied: the source region of the strong earthquake has the media structure with the relatively high seismic velocity and high resistivity, there exists the intracrustal low velocity and high conductivity layer bellow it and the strong earthquakes occur near the transitional zone of the crustal brittle to ductile deformation. These characteristics are the generality of the generating environments of strong earthquakes. However, the specific seismogenic tectonic environments and action of the stress field of the seismic source in the various regions, correspondingly constrains the dislocation and rupture mechanical mechanism of source fault of strong earthquake.

华南地壳岩石弹性和变形性质的高温高压实验研究

The South continent of China lies to southeast of Eurasia block. It is an active area from the view of crust growth and continent spread and is a transition zone between continental crust and oceanic crust. The compressional wave velocities and anisotropies of typical crustal metamorphic rocks were determined at high temperature (up to 1000 ℃) and high pressure(up to 800MPa). The experimental results show that the velocities generally increase with pressure, and is unaffected by temperature up to around 550 ℃. But the velocities of all experimental samples start to drop above a temperature point. For an example, this greatly reduce the speed of wave propagation in amphibolite and serpentinite above 760 ℃ and above 550 ℃ respectively, which may be due to dehydrate of amphibole and serpentine. P-wave anisotropy coefficients of those rocks range from 2% to 10% at 800MPa and 500 ℃. The anisotropies decrease with increasing pressure at room temperature, but hardly change as function of temperature at constant 800MPa or 600MPa pressure. The average velocity of the six crustal rocks is 6.28km/s under the condition of 800MPa and 550 ℃, which is consistent with the result of deep seismic sounding data. Based on this experimental result, we deduce there may exist a lot of felsic granulites and amphibolites at the depth of 15-25km underground. With increasing temperature and pressure, the deformation behavior of the rocks undergoes from localized brittle fracture, semi-brittle deformation (cataclastic flow or semi-brittle faulting, semi-brittle flow) to homogeneous crystal-plastic flow. This transition is associated with mechanical behavior and micro-mechanism. It is very important to understanding earthquake source mechanics, the strength of the lithosphere and the style of deformation. The experiments were conducted at temperature of 600-1000 ℃, confining pressure of 500MPa, and stain rates of 10~(-4)-10~(-6) S~(-1). For fine-grained natural amphibolite, the results of experiments show that brittle faulting is major failure mode at temperature <600 ℃, but crystal-plastic deformation is dominate at temperature >800 ℃, and there is a transition with increasing temperature from sembrittle faulting to cataclastic flow and sembrittle flow at temperature of 670-750 ℃. For medium-grained natural Felsic granulite, the results of experiments show that brittle faulting is major failure mode at temperature <500 ℃, but crystal-plastic deformation is dominate at temperature >700 ℃, and there is a transition with increasing temperature from semibrittle faulting to cataclastic flow and sembrittle flow at temperature of 500-600 ℃.

Lg尾波衰减成像研究——北京及邻区衰减成像

With the development of the technology of earthquake observation, more and more researchers work at many fields' of seismicity using seismic kinetic property, as the result, the study of attenuation has also made great progress, especially in the mechanism of the attenuation and the physical process. Aki put forward single back scattering theory to explain the forming of the seismic coda wave in 1969. Then, researchers started to develop the study in seismic scattering and attenuation. My thesis is also based on that theory. We assume that the Lg wave is a superposition fo high-mode surface waves, the coda of Lg is caused by scattering. Sato proposed Single Isotropic Scattering model (SIS model) to interpreted the scatter property, and he also formulated the geometrical spreading term. Then Xie (1988) developed the single spectral-ratio (SSR) method to obtain the Lg coda Q and the frequency dependent factor n. Later, he get to lateral images in the area of scatter ellipse. SSR method is explored and used in the study of Lg coda waves of regional earthquakes in my thesis. Choosing the earthquakes records with high ratio of signal-noise ,which were recorded at the stations from 1989 to 1999, we obtain the single trace Lg coda Q and its frequency dependent factor n. The results proved that SIS model is the reasonable model to explain the Lg coda wave, and SSR method also can be used to process Lg coda of regional earthquakes to get to the satisfied Lg coda Q. Based on the Lg coda Q we obtained using the former method, we explore the programs to inverse the regional Lg coda Q independently, and then make use of them to inverse the Lg coda Q of Beijing and adjacent area. The inversion result is satisfied. We conclude that the distribution of Qo (Q in lHz) is marked by the inhomogeneity, which is related to the tectonic structure: The value of Qo in uplift area, for example, Yanshan uplift, Taihang uplift, Luxi Uplift, is higher than the depression area, for example, Jizhong depression, Huanghua depression, and Jiyang depression, and the border between the higher Q area and lower Q area is very clear; Lg coda Q is also related to the velocity structure, higher velocity area is also with higher Q, lower velocity area is with lower Q; and higher heat-flow area is companied with lower Q. All in all, the value of Q reflects the difference of characteristics of lithofaces, porosity, the liquid content between the pores and heat flow. So, the Q value difference between uplift area and depression area reveals the difference of tectonic structure, lithology and physical character of the rock. So, the study of Lg coda Q is help to understand the earthquakes propagation mechanism through the inhomogenous medium, the cause of the coda, attenuation mechanism of the coda. Making use of the lateral images of Q, with velocity images, heat flow results, and other experimental result, we will be promoted to understand the complex structure of the crust, its inhomogenous character, and so on.

边坡动力响应分析及应用研究

As a marginal subject, dynamic responses of slopes is not only an important problem of engineering geology (Geotechnical problem), but also of other subjects such as seismology, geophysics, seismic engineering and engineering seismic and so on. Owning to the gulf between different subjects, it is arduous to study dynamic responses of slopes and the study is far from ripeness. Studying on the dynamic responses of slopes is very important in theories as well as practices. Supported by hundreds of bibliographies, this paper systemically details the development process of this subject, introduces main means to analyze this subject, and then gives brief remarks to each means respectively. Engineering geology qualitative analysis is the base of slopes dynamic responses study. Because of complexity of geological conditions, engineering geology qualitative analysis is very important in slopes stability study, especially to rock slopes with complex engineering geology conditions. Based on research fruits of forerunners, this paper summarizes factors influencing slopes dynamic stability into five aspects as geology background, stratums, rock mass structure, and topography as well as hydrogeology condition. Based on rock mass structure controlling theory, engineering geology model of the slope is grouped into two typical classes, one is model with obvious controlling discontinuities, which includes horizontal bedded slope, bedding slope, anti-dip slope, slide as well as slope with base rock and weathered crust; the other is model without obvious controlling discontinuities, which includes homogeneous soil slope, joint rock mass slope. Study on slope failure mechanism under dynamic force, the paper concludes that there are two effects will appear in slope during strong earthquake, one is earthquake inertia force, the other is ultra pore pressure buildup. The two effects lead to failure of the slope. To different types of slope failure, the intensity of two effects acting on the slope is different too. To plastic flow failure, pore pressure buildup is dominant; to falling rock failure and toppling failure, earthquake inertia force is dominant in general. This paper briefly introduces the principle of Lagrangian element method. Through a lot of numerical simulations with FLAC3D, the paper comprehensively studies dynamic responses of slopes, and finds that: if the slope is low, displacement, velocity and acceleration are linear enlarging with elevation increasing in vertical direction; if the slope is high enough, displacement, velocity and acceleration are not linear with elevation any more, on the other hand, they fluctuate with certain rhythm. At the same time, the rhythm appears in the horizontal direction in the certain area near surface of the slope. The distribution form of isoline of displacement, velocity and acceleration in the section of the slope is remarkably affected by the slope angle. In the certain area near the slope surface, isoline of displacement, velocity and acceleration is parallel to the surface of the slope, in the mean time, the strike direction of the extreraum area is parallel to the surface of the slope too. Beyond this area, the isoline direction and the strike direction of the extremum area turn to horizontal with invariable distance. But the rhythm appearing or not has nothing to with the slope angle. The paper defines the high slope effect and the low slope effect of slopes dynamic responses, discusses the threshold height H^t of the dynamic high slope effect, and finds that AW is proportional to square root of the dynamic elastic moduli El P , at the same time, it is proportional to period Tof the dynamic input. Thus, the discriminant of H^t is achieved. The discriminant can tell us that to a slope, if its height is larger than one fifth of the wavelength, its response regular will be the dynamic high slope effect; on the other hand, its response regular will be the dynamic low slope effect. Based on these, the discriminant of different slopes taking on same response under the same dynamic input is put forward in this paper. At the same time, the paper studies distribution law of the rhythm extremum point of displacement, velocity and acceleration, and finds that there exists relationship of N = int among the slope height H, the number of the rhythm extremum VHlhro) point N and ffthre- Furthermore, the paper points out that if N^l, the response of the slope will be dynamic high slope effect; \fN

中国大陆及邻区地震活动背景、环境触发与地震预测研究

This dissertation that includes most of the P. PH.D research work during 2001~2002 covers the large-scale distribution of continental earthquakes in mainland China, the mechanism and statistic features of grouped strong earthquakes related to the tidal triggering, some results in earthquake prediction with correlativity analysis methods, and the flushes from the two strong continental earthquakes in South Asia in 2001. Mainland China is the only continental sub-plate that is compressed by collision boundaries at its two sides, within which earthquakes are dispersive and distributed as seismic belts with different widths. The control capability of the continental block boundaries on the strong earthquakes and seismic hazards is calculated and analyzed in this dissertation. By mapping the distribution of the 31282 ML:3s2,0 earthquakes, I found that the depth of continental earthquakes depend on the tectonic zonings. The events on the boundaries of relatively integrated blocks are deep and those on the new-developed ruptures are shallow. The average depth of earthquakes in the West of China is about 5km deeper than that in the east. The western and southwestern brim of Tarim Basin generated the deepest earthquakes in mainland China. The statistic results from correlation between the grouped M7 earthquakes and the tidal stress show that the strong events were modulated by tidal stress in active periods. Taking Taiwan area as an example, the dependence of moderate events on the moon phase angles (￡>) is analyzed, which shows that the number of the earthquakes in Taiwan when D is 50° ,50° +90° and 50° +180° is more than 2 times of standard deviation over the average frequency at each degree, corresponding to the 4th, 12th and 19th solar day after the new moon. The probability of earthquake attack to the densely populated Taiwan island on the 4th solar day is about 4 times of that on other solar days. On the practice of earthquake prediction, I calculated and analyzed the temporal correlation of the earthquakes in Xinjinag area, Qinghai-Tibet area, west Yunnan area, North China area and those in their adjacent areas, and predicted at the end of 2000 that it would be a special time interval from 2001 to 2003, within which moderate to strong earthquakes would be more active in the west of China. What happened in 2001 partly validated the prediction. Within 10 months, there were 2 great continental earthquakes in south Asia, i.e., the M7.8 event in India on Jan 26 and M8.1 event in China on Nov. 14, 2001, which are the largest earthquake in the past 50 years both for India and China. No records for two great earthquakes in Asia within so short time interval. We should speculate the following aspects from the two incidences: The influence of the fallacious deployment of seismic stations on the fine location and focal mechanism determination of strong earthquakes must be affronted. It is very important to introduce comparative seismology research to seismic hazard analysis and earthquake prediction research. The improvement or changes in real-time prediction of strong earthquakes with precursors is urged. Methods need to be refreshed to protect environment and historical relics in earthquake-prone areas.

接收函数方法与中国及邻区上地幔间断面的研究

The receiver function method applied in researching the discontinuities in upper mantle was systematically studied in this paper. Using the theoretical receiver functions, the characteristics of P410S and P660S phases were analyzed, and the influencing factors for detection of these phases were discussed. The stability of receiver function was studied, and a new computational method of receiver function, RFSSMS (Receiver Function of Stack and Smooth of Multi seismic-records at a Single station), was put forward. We built initial reference velocity model for the media beneath each of 18 seismic stations respectively; then estimated the buried depths of 410-km and 660-km discontinuities(simply marked as '410' and '660') under the stations by using the arrive time differences of P410S and P660S with P. We developed a new receiver function inversion method -PGARFI (Peeling-Genetic Algorithm of Receiver Function Inversion), to obtain the whole crust and upper mantle velocity structure and the depths of discontinuities beneath a station. The major works and results could be summarized as follows: (1) By analysis of the theoretical receiver functions with different velocity models and different ray parameters, we obtain the knowledge: The amplitudes of P410S and P660S phases are decreasing with the increasing of epicentral distance A , and the arrival time differences of these phases with P are shorter as A is longer. The multiple refracted and/or reflected waves yielded on Moho and the discontinuities in the crust interfere the identification of P410S. If existing LVZ under the lithosphere, some multiple waves caused by LVZ will interfere the identification of P410S. The multiple waves produced by discontinuity lied near 120km depth will mix with P410s phase in some range of epicentral distance; and the multiple waves concerned with the discontinuity lied near 210km depth will interfere the identification of P660S. The epicentral distance for P4i0s identification is limited, the upper limit is 80° . The identification of P660S is not restricted by the epicenter distance obviously. The identification of P410S and P6gos in the theoretical receiver functions is interfered weakly from the seismic wave attenuation caused by the media absorption if the Q value in a reasonable range. (2) The stability of receiver function was studied by using synthetic seismograms with different kind of noise. The results show that on the condition of high signal-noise-ratio of seismic records, the high frequency background noise and the low frequency microseism noise do not influence the calculating result of receiver function. But the media "scattering noise" influence the stability of receiver function. When the scattering effect reach some level, the identification of P4iOs and P66os is difficult in single receiver function which is yielded from only one seismic record. We provided a new method to calculate receiver function, that is, with a group of earthquake records, stacking the R and Z components respectively in the frequency domain, and weighted smooth the stacked Z component, then compute the complex spectrum ratio of R to Z. This method can improve the stability of receiver function and protrude the P4i0s and P66os in the receiver function curves. (3) 263 receiver functions were provided from 1364 three component broadband seismograms recorded at 18 stations in China and adjacent areas for the tele-earthquakes. The observed arrival time differences of P410S and P660S with P were obtained in these receiver functions. The initial velocity model for every station was built according to the prior research results. The buried depths of '410' and '660' under a station were acquired by the way of adjusting the depths of these two discontinuities in the initial velocity model until the theoretical arrival time differences of P410S and P660S with P well conformed to the observed. The results show an obvious lateral heterogeneity of buried depths of ' 410' and (660' . The depth of '410' is shallower beneath BJI, XAN, LZH and ENH, but deeper under QIZ and CHTO, and the average is 403km . The average depth of '660' is 663km, deeper under MDJ and MAJO, but shallower under QIZ and HYB. (4) For inversing the whole crust and upper mantle velocity structure, a new inversion method -PGARFI (Peeling-Genetic Algorithm of Receiver Function Inversion) has- been developed here. The media beneath a station is divided into segments, then the velocity structure is inversed from receiver function from surface to deep successively. Using PGARFI, the multi reflection / refraction phases of shallower discontinuities are isolated from the first order refraction transform phase of deep discontinuity. The genetic algorithm with floating-point coding was used hi the inversion of every segment, and arithmetical crossover and non-uniform mutation technologies were employed in the genetic optimization. 10 independent inversions are completed for every segment, and 50 most excellent velocity models are selected according to the priority of fitness from all models produced in the inversion process. The final velocity structure of every segment is obtained from the weighted average of these 50 models. Before inversion, a wide range of velocity variation with depth and depth range of the main discontinuities are given according to priori knowledge. PGARFI was verified with numerical test and applied in the inversion of the velocity structure beneath HIA station down to 700km depth.