Seismic wave propagation in a viscoelastic porous solid saturated by viscous liquid

A general solution is deduced of the differential equations describing the propagation of elastic waves in a dissipative liquid-filled viscoelastic porous solid. The velocities of three existing waves have been expressed in convenient form using the moduli of the solid phase and by introducing the frequency-dependent equivalent mass densities. The solution is then used to examine some of the phenomena which arise when each of the three-body waves, in turn, are incident on a traction-free plane boundary. Analytic expressions for the reflection coefficients are obtained. Numerical calculations have been made, for a particular model, in case of incidentP _I wave. Effect of viscoelasticity and viscosity on the reflection coefficients has also been exhibited.     

Elastic finite difference modelling of lower crustal reflections

It is a common feature to observe on deep reflection profiles, short (less than the Fresnel area diameter) and strongly discontinuous lower crustal reflections. Such wave patterns can be attributed to variations in the crustal properties on the scale of a few wavelengths. In order to explain these characteristics, we have computed finite-difference synthetic seismograms for various types of deep heterogeneities. Focusing, defocusing and interference effects were especially studied. The results can only be interpreted in a qualitative manner because our models exhibit departures from the real cases (lower frequency content, and only two-dimensional structures). It is found that simple undulations of the deep interfaces can hardly produce the discontinuous pattern observed, but high velocity intrusions generate complex interferences matching the reflection character of real data. Furthermore, the reflection patterns strongly depend both on length and shape of the inclusions.     

RESEARCH ON NEOGENE-QUATERNARY STRATIGRAPHIC STRUCTURE AND SHALLOW TECTONIC FEATURES IN THE NORTH SECTION OF DAXING FAULT ZONE BASED ON SHALLOW SEISMIC REFLECTION PROFILING

The Daxing Fault is an important buried fault in the Beijing sub-plain, which is also the boundary fault of the structural unit between Langgu sub-sag and Daxing sub-uplift. So far, there is a lack of data on the shallow tectonic features of the Daxing Fault, especially for the key structural part of its northern section where it joins with the Xiadian Fault. In this paper, the fine stratigraphic classifications and shallow tectonic features of the northern section in the main Daxing Fault are explored by using three NW-trending shallow seismic reflection profiles. These profiles pass through the Daxing earthquake(M6¾)area in 1057AD and the northern section of the main Daxing Fault. The results show that seven strong reflection layers(T₀₁—T₀₃, T_Q and T₁₁—T₁₃)are recognized in the strata of Neogene and Quaternary beneath the investigated area. The largest depth of strong reflection layer(T₁₃)is about 550~850ms, which is interpreted as an important surface of unconformity between Neogene and Paleogene or basement rock. The remaining reflection layers, such as T₀₁ and T_Q, are interpreted as internal interfaces in Neogene to Quaternary strata. There are different rupture surfaces and slip as well as obviously different structural features of the Daxing Fault revealed in three shallow seismic reflection profiles. The two profiles(2-7 and 2-8)show obvious rupture surfaces, which are the expression of Daxing Fault in shallow strata. Along the profile(2-6), which is located at the end of the Daxing fault structure, a triangle deformation zone or bending fracture can be identified, implying that the Daxing Fault is manifested as bending deformation instead of rupture surfaces at its end section. This unique structural feature can be explained by a shearing motion at the end of extensional normal fault. Therefore, the Daxing Fault exhibits obviously different tectonic features of deformation or displacement at different structural locations. The attitude and displacement of the fault at the shallow part are also different to some extent. From the southwest section to the northeast section of the fault, the dip angle gradually becomes gentler(80°~60°), the upper breakpoint becomes deeper(160~600m), and the fault displacement in Neogene to Quaternary strata decreases(80~0m). Three shallow seismic reflection profiles also reveal that the Daxing Fault is a normal fault during Neogene to early Quaternary, and the deformation or displacement caused by the activity of the fault reaches the reflection layer T₀₂. This depth is equivalent to the sedimentary strata of late Early-Pleistocene. Therefore, the geometry and morphology of the Daxing Fault also reveal that the early normal fault activity has continued into the Early Pleistocene, but the evidence of activity is not obvious since the late Pleistocene. The earthquakes occurring along the Daxing Fault, such as Daxing earthquake(M6¾)in 1057AD, may not have much relation with this extensional normal fault, but with another new strike-slip fault. A series of focal mechanism solutions of modern earthquakes reveal that the seismic activity is closely related to the strike-slip fault. The Daxing Fault extends also downwards into the lower crust, and may be cut by the steeply dipping new Xiadian Fault on deep seismic reflection profile. The northern section of the Daxing Fault strikes NNE, with a length of about 23km, arranged in a right step pattern with the Xiadian Fault. Transrotational basins have been developed in the junction between the northern Daxing Fault and the southern Xiadian Fault. Such combined tectonic features of the Daxing Fault and Xiadian Fault evolute independently under the extensional structure background and control the development of the Langgu sub-sag and Dachang sub-sag, respectively.     

测量学教学主体转换改革及试验

探讨了建筑工程专业《测量学》教学方法,转换教学主体,精简教学内容,改革《测量学》理论教学和实践教学。     

高校实验室建设在教学和科研中的地位和作用

高校实验室是学科建设,科学研究和人才培养的重要基地,也是对学生进行综合素质教育的重要课堂,反映了高校的教学、科研和管理水平     

桥头集-东关断裂合肥盆地段活动特征

北西走向的桥头集-东关断裂与郯庐断裂带南段相交切，横跨合肥盆地及其东缘的隆起区，在合肥盆地内呈隐伏状态。本研究跨桥头集-东关断裂合肥盆地段布设3条浅层地震勘探测线，揭示断裂浅部构造特征。解译出的F_P1、F_P2和F_P3断层性质相同，倾向一致，上断点深度相近，反映出桥头集-东关断裂合肥盆地段是一条走向NW、倾向SW、具有逆断分量的断裂。3条浅层地震反射剖面中第四系的底界面反射波组T_Q呈连续近水平展布，表明桥头集-东关断裂两侧的第四系厚度无明显变化。在浅震剖面解译的基础上，布设了1条跨断层钻孔联合剖面，剖面揭露出的第四系没有被错动。结合本区第四系地层发育情况及钻孔地层年龄分析，认为桥头集-东关断裂中更新世以来不活动。根据本文探测结果，尚不能排除桥头集-东关断裂早更新世有一定的弱活动。     

数字测图实践教学的启示

探讨了实践教学在培养大学生综合素质方面的作用、实践教学与课堂教学的关系 ,以及开展数字测图实践教学活动的有关问题。并倡导广大同行就如何推进数字测图实践教学内容、方法、及手段的改革、促进实践教学水平的提高 ,展开交流研讨     

构建复合型人才培养的测绘工程实践教学新体系

基于培养复合型测绘人才的需要，本文较系统地提出了应从实践教学课程体系及实验内容、实验教学方法、实验教学质量管理、实验环境和条件等几个方面进行改革、整合，从而构建测绘工程实践教学新体系。     

受污染的云滴内NOx光化通量的计算

依靠云滴的射线光学模型,针对具有吸收的耗散介质,可得到形式完整的电磁波反射系数公式,并且可求得具有几何意义的实际折射角。文中重点讨论了云滴中污染内含物及其不同的内混合方式对光化通量增强因子的影响。结果表明:云滴的存在都能增强光子的光化通量,仅当吸收系数非常大时,云滴内光化通量才会减小;无论哪一种内混合方式,受污染的云滴内光化通量增强基本上稍大于先前的估计值;光化通量增强因子一般都在1.2～1.62之间,即光化通量增加了20%～62%;吸收系数为零时,增强因子与云滴半径无关;增强因子随云滴半径和吸收系数的增大而减小。当云滴半径接近1μm时,吸收系数的影响迅速减小。     

Elevated lateral stress in unlithified sediment, Midcontinent, United States—geotechnical and geophysical indicators for a tectonic origin

Indirect and direct geotechnical measurements revealed the presence of high lateral earth pressure (K_o) in shallow, unlithified sediment at a site in the northernmost Mississippi embayment region of the central United States. Results from pile-load and pressuremeter tests showed maximum K_o values greater than 10; however, the complex geologic environment of the Midcontinent made defining an origin for the anomalous K_o based solely on these measurements equivocal. Although in situ sediment characteristics indicated that indirect tectonic or nontectonic geologic mechanisms that include transient overburden loads (e.g., fluvial deposition/erosion, glacial advance/retreat) and dynamic shear loads (e.g., earthquakes) were not the dominant cause, they were unable to provide indicators for a direct tectonic generation. Localized stresses induced anthropogenically by the geotechnical field tests were also considered, but ruled out as the primary origin. A high-resolution shear-wave (SH) reflection image of geologic structure in the immediate vicinity of the test site revealed compression-style neotectonism, and suggested that the elevated stress was a tectonic manifestation. Post-Paleozoic reflectors exhibit a Tertiary (?) structural inversion, as evidenced by post-Cretaceous fault displacement and pronounced positive folds in the hanging wall of the interpreted faults. The latest stratigraphic extent of the stress effects (i.e., all measurements were in the Late Cretaceous to Tertiary McNairy Formation), as well as the relationship of stress orientation with the orientation of local structure and regional stress, remain unknown. These are the subjects of ongoing studies.