Modeling the seismic response of basin-edge structure by a sequential waveform method

A sequential waveform method is developed to simulate the seismic response of basin-edge structure excited by a plane incident P-wave. The full procedure involves: (a) a previous parameterization of the investigated model using the seismic wave velocities and depths of the sedimentary stratifications; (b) an input motion determined from the records at stations installed on hard rock; (c) forward computation of the P-SV elastic wave field by means of a two-dimensional finite difference (FD) method; (d) the optimization of the model vector using simulated annealing technique and comparing the simulated seismic response of the tested structure with the observed wave field; (e) the correction of the initial model by trial-and-error by testing the differences between synthetics and observed data, and (f) the final solution obtained by iteration using the conjugate gradient algorithm. The search of an optimal basin-edge model has been parallel processed by varying the shapes and velocities of strata on the basis of the fitting of relative timing, amplitude and phase between the output and the observed data. The input motion and sensitivity have been checked and the validity of the method has been demonstrated by numeric analysis. Using the teleseismic records generated by 7 earthquakes recorded at 26 broadband seismic stations, we have studied the seismic velocity structure of the southern edge of the Jiyang depression located in the Bohai Bay basin, northern China. Two cross sections show an agreement between the velocity results and the geological sections available in the region. In addition, we obtain evidence of three hidden faults under the sections and features that suggest major extensions at the Paleogene.     

位场各阶垂向导数换算的新正则化方法

位场垂向导数大量应用于位场数据处理与解释中.当前广泛采用的位场各阶垂向导数换算方法为基于Laplace方程并结合波数域和空间域方法的具有递推特性的ISVD(integrated second vertical derivative)算法.本文在位场垂向导数换算的正则化方法和径向平均功率谱的基础上,提出一种位场各阶垂向导数换算的新正则化方法.新正则化方法仅需通过分析位场径向平均功率谱来确定一个截止波数,即可稳定换算位场各阶垂向导数.理论模型和实测数据实验结果表明:(1)新正则化方法物理意义明确、计算简单,且各阶垂向导数换算的稳定性和精度明显优于ISVD算法;(2)在用新正则化方法求得各阶垂向导数的基础上,利用泰勒级数法可以获得大深度、高精度的位场向下延拓结果.     

攀西地区重力场特征及地壳密度结构

攀西地区位于峨眉山大火成岩省中西部,构造和岩浆特征显著,地震活动强烈.通过对野外重力测量得到的云县—会东和普洱—七甸两条剖面的高精度重力观测数据进行处理和分析,构建了沿剖面的二维地壳密度结构,其中普洱—七甸剖面与孟连—马龙宽角地震剖面部分位置重合.同时结合区域重力异常特征及下地壳视密度填图结果,得到如下初步认识:红河断裂带是南北地震带南段地区重要的构造分界线,断裂带南北向密度结构和莫霍面分布形态存在较大差异,沿走向构造变化.云县—会东剖面上大姚—会东段下地壳底部存在密度较高的壳幔过渡层,结合研究区下地壳底部壳幔过渡层的密度分布特征,认为该过渡层不是攀西裂谷下的"裂谷垫",而是由岩浆底侵作用造成的.     

一种基于LEO卫星信标的电离层层析成像新算法

LEO卫星信标是电离层监测的重要手段之一. 利用电离层层析成像算法, LEO卫星信标能够实现区域电离层电子密度的快速重构. 针对LEO卫星信标的特点, 本文提出了一种函数基模型与像素基模型组合的电离层层析成像新算法. 选择差分相对电离层总电子含量作为输入数据源, 先通过函数基模型法获取电离层电子密度初始分布, 再利用像素基模型法对初始分布进行二次迭代重构, 该方法可有效降低电离层层析成像对背景电离层模型的依赖, 同时能够实现电离层小尺度扰动结构的有效反演. 利用数值仿真方法及低纬度电离层层析成像网的实测数据的反演结果验证了本文提出的新算法的可行性和可靠性.     

南北地震带南段地壳厚度重震联合最优化反演

重力反演方法是研究地壳结构和物性界面起伏的有效地球物理手段之一.本文收集了南北地震带南段67个已有的固定台站接收函数反演的Moho面深度结果,并使用基于EGM2008重力异常模型计算的布格重力异常,验证了本文提出的重震联合密度界面反演方法的有效性.利用接收函数对台站下方Moho面深度估计作为先验约束,定义了一类评价函数,通过对重力反演算法中尺度因子,平移因子和稳定性因子的最优选择,最小化重力反演结果与接收函数模型之间的差异.结果表明,本文提出的方法,可以有效地同化不同地球物理方法获得的反演模型,且通过重震联合反演可以改进由于对空间分布不均匀的接收函数结果插值可能而引起的误差.本文还通过引入Crust1.0的Moho面深度为初值,同时考虑地壳密度的横向不均匀分布,通过模型之间的联合反演有效改善了地球物理反演模型间的不一致性问题.本文反演得到的最优化Moho面深度模型与已知67个台站位置接收函数模型之间的标准差约1.9 km,小于Crust1.0与接收函数结果模型之间标准差为3.73 km的统计结果.本文研究结果对于同化重震反演结果、精化地壳密度界面模型,都具有十分重要的参考意义.     

华北地区热均衡、重力均衡与深部构造

本文基于最新的全球重力场模型TopexV18.1数据,在区域背景尺度下,计算了华北地区的区域布格重力异常,并反演了Moho面分布特征;在此基础上结合区域地热流测量数据,讨论重力均衡和热均衡调整过程对现今地形的影响;最后,结合已有的速度结构模型和岩石圈热参数,对10个次级块体单元的热均衡特点开展了综合对比研究.研究结果表明:华北地区构造块体单元之间由于克拉通底部受到不同程度的破坏,不仅深部构造特征差异性明显,而且其构造热均衡特点也不尽相同.根据平均地震波速去掉重力均衡作用后恢复的高程-热流关系表明,均衡作用对于现今地形的改造作用十分显著,但根据该方法对燕山隆起和冀中坳陷两个块体的恢复效果不明显.     

太湖水体光学衰减系数的特征及参数化

利用2001-2002年周年太湖全湖不同湖区湖泊光学及表层水样的实测资料,分析了太湖水体表层光学衰减系数与透明度、无机和有机颗粒物质及叶绿素a的相关关系,建立了表层水光学衰减系数与无机、有机颗粒物质及叶绿素a多元线性回归方程。结果表明,光学衰减系数与透明度的关系为：Kdg0.096 1.852/ST;表层水光学衰减系数与无机、有机颗粒物质及叶绿素a多元线性回归方程为：Kd=0.219 0.0768Ciss 0.214Cdet 0.006Cchl;光学衰减系数变化的主要影响因子是无机及有机颗粒物。     

The optimization of satellite orbit for Space-VLBI observation

By sending one or more telescopes into space,Space-VLBI(SVLBI)is able to achieve even higher angular resolution and is therefore the trend of the VLBI technique.For the SVLBI program,the design of satellite orbits plays an important role for the success of planned observation.In this paper,we present our orbit optimization scheme,so as to facilitate the design of satellite orbits for SVLBI observation.To achieve that,we characterize the uv coverage with a measure index and minimize it by finding out the corresponding orbit configuration.In this way,the design of satellite orbit is converted to an optimization problem.We can prove that,with an appropriate global minimization method,the best orbit configuration can be found within the reasonable time.Besides that,we demonstrate that this scheme can be used for the scheduling of SVLBI observations.     

Gas migration behavior in saturated bentonite under flexible conditions with consideration of temperature effects

Acta Geotechnica - Investigation of thermal effects on gas migration behavior in saturated bentonite materials is of great significance for the assessment of long-term safety and performance...