浅层地震在复杂断裂带探测中的应用研究

拟建中的潍河特大桥地处沂沭大断裂边缘。区内断裂发育,构造复杂,直接会影响大桥基础的稳定性,因而查清区内断裂带的准确位置与分布是大桥工程的关键。探测应用浅层地震折射波方法和选用追逐与相遇观测系统和大小排列相结合的工作方法,准确地查明了区内断裂的准确位置和特征,与钻井资料对比,十分吻合。     

折射层析成像法测试隧道围岩松动圈

通过应用折射层析成像法在乌鞘岭特长隧道中的测试,说明该方法对于横向速度变化不均一,过渡带速度渐变的地质情况具有分辨率高、图像直观、易于解释,适合对隧道围岩松动圈的测试.     

电磁波信号在对流层中路径弯曲改正的级数展开式

大气折射延迟是空间大地测量中的一个主要误差源。本文严格地给出了中性大气路径弯曲改正的原理性公式。通过对各种因素量级的分析,在亚毫米量级的精度上给出了一个以视天顶距正切和正割乘积为参数的级数展开模型。新模型在球对称大气模型下,级数展开模型的精度达到了毫米量级,理论上可以展开到任意阶次,且可允许观测高度角小到5°。     

A seismic refraction study of cretaceous oceanic lithosphere in the Northwest Pacific Basin

A seismic refraction study on old (110 Myr) lithosphere in the northwest Pacific Basin has placed constraints on crustal and uppermantle seismic structure of old oceanic lithosphere, and lithospheric aging processes. No significant lateral variation in structure other than azimuthally anisotropic mantle velocities was found, allowing the application of powerful amplitude modeling techniques. The anisotropy observed is in an opposite sense to that expected, suggesting the tectonic setting of the area may be more complex than originally thought. Upper crustal velocities are generally larger than for younger crust, supporting current theories of decreased porosity with crustal aging. However, there is no evidence for significant thickening of the oceanic crust with age, nor is there any evidence of a lower crustal layer of high or low velocity relative to the velocity of the rest of Layer 3. The compressional and shear wave velocities rule out a large component of serpentinization of mantle materials. The only evidence for a basal crustal layer of olivine gabbro cumulates is a 1.5 km thick Moho transition zone. In the slow direction of anisotropy, upper mantle velocities increase from 8.0 km s^-1 to 8.35 km s^-1 in the upper 15 km below the Moho. This increase is inconsistent with an homogeneous upper mantle and suggests that compositinal or phase changes occur near the Moho.     

Phase-array decomposition of a seismic section

A seismic re fraction/wide-angle reflection profile is analysed for the presence of correlated events ('phases'). The correlation problem is formulated in terms of temporally, spatially and frequency-local complex covariances. For robustness, the method concentrates on phase rather than amplitude information. This allows a computationally efficient algorithm that can make allowance for signal correlation length and can model curved wavefronts. A statistical test based on residual phase misfit across the analysed subarray is used to assess the probability that a detected event represents a real correlated signal.
With our chosen analysis parameters and confidence level (over 99.9 per cent). 1222 events were detected in the data. Using simple techniques based on 1-D earth models, detected events are associated with a small number of particular wave types. In this way, we have succeeded in classifying almost 95 per cent of the detected events. Those that remain describe those components of the data that are inconsistent with our simple ray paths in the 1-D assumption and with our prescribed tolerance. These include reverberations, near-surface guided waves and reflected waves from strongly laterally inhomogeneous structures. According to our modelling, about 25 per cent of the detected events are consistent with simple P -wave reflected energy, and these are to a very large extent (over 85 per cent) distinct from all the other wave-type models we have used. A direct mapping of the detected events into the offset-depth domain reveals dear internal and external consistencies among the detections for the various wave types. Estimated earth structure is consistent with models from previous analyses based on much larger data sets.
We have thus succeeded in extracting correlated events from the data and decomposing these, approximately but meaningfully, into distinct classes (ray paths)     

龙门山断裂带南段地壳电性特征: 来自速度结构约束下大地电磁反演的证据

龙门山断裂带区域内大震频发、构造运动活跃, 其地史演化与隆升动力学机制一直未有定论.2013年4月20日雅安大地震后, 于小金至雅安段布设了一条垂直于龙门山构造带长约200 km的大地电磁剖面.为了克服龙门山地形起伏影响, 同时增强大地电磁反演的垂向分辨率, 本文采用宽角折/反射地震走时反演获得的速度模型作为结构约束, 通过交叉梯度项引入大地电磁非线性共轭梯度二维反演, 实现了考虑地形的速度结构约束大地电磁二维算法.设计地堑-地垒模型进行合成数据反演试算, 结果显示基于速度结构约束的带地形二维大地电磁反演算法能够减少由地形影响引起的假异常, 同时对异常体边界轮廓的刻画更加清晰.实测数据未加地震资料约束的大地电磁二维反演结果, 具有明显"低-高-低"的宏观电性特征, 与前人结果基本吻合.本文将新算法应用于实测数据反演的结果表明: 松潘—甘孜地块下方包含两部分低阻异常带, 并有相互连通趋势.西侧低阻体埋深更深, 分布于15~45 km范围内, 顶部有通道延伸至地表; 东侧低阻体相对变浅, 向东逐渐延伸至高阻异常体之上, 具有向扬子地体逆冲推覆的趋势.龙门山构造带薄皮盖层下方大规模高阻异常体厚约50 km, 以Moho面为底界, 且呈现北西倾向的特征, 与人工地震资料推测的龙门山三条主断裂的深部延伸的产状一致.     

时间平均基流中准定常波的传播及多向折射

应用几何光学中的射线理论，直观地讨论了准定常波在时间平均基流中的传播，解释了定常 传播的纬向非均匀性。结果表明：折射指数平方可表示为基流绝对对基流流函数的微商，定常波的传播路径与折射指数平方的空间分布有着密切的关系。