龙门山断裂带卫星重力场特征及其发震机制

为了整体了解青藏高原东南缘龙门山断裂带的卫星重力场特征及其发震机制,文中基于重力卫星数据展现出研究区域的地形信息,并通过解算反映莫霍面起伏的区域重力异常,反演出研究区域的莫霍面深度,同时运用GPS速度场数据探测了研究区域地壳的形变速率及方向;最后,结合龙门山断裂带的构造背景及前人已有的深部探测结果,分析其发震前后重力时变场的动态特征并探讨了发震机理。研究结果表明:青藏高原东缘深部物质逐年向E流展,在龙门山断裂带处强势受阻,持续的挤压、碰撞过程形成了深部莫霍面的"陡降带",长期的应力作用利于逆冲推覆和走滑构造的形成;龙门山地震带震前处于明显的重力变化梯度带,深部物质运移的流速差异大,流体压力增强,有助于地壳流体入侵和软流圈物质底侵上涌;物质和能量的持续积累最终将导致深部应力严重失衡、深部薄弱构造剪切破裂,从而发生逆冲、推覆构造运动的大地震。

Near-source noise suppression of AMT by compressive sensing and mathematical morphology filtering

In deep mineral exploration, the acquisition of audio magnetotelluric （AMT） data is severely affected by ambient noise near the observation sites; This near-field noise restricts investigation depths. Mathematical morphological filtering （MMF） proved effective in suppressing large-scale strong and variably shaped noise, typically low-frequency noise, but can not deal with pulse noise of AMT data. We combine compressive sensing and MMF. First we use MMF to suppress the large-scale strong ambient noise; second, we use the improved orthogonal match pursuit （IOMP） algorithm to remove the residual pulse noise. To remove the noise and protect the useful AMT signal, a redundant dictionary that matches with spikes and is insensitive to the useful signal is designed. Synthetic and field data from the Luzong field suggest that the proposed method suppresses the near-source noise and preserves the signal well; thus, better results are obtained that improve the output of either MMF or IOMP.

Power-line interference suppression of MT data based on frequency domain sparse decomposition

Power-line interference is one of the most common noises in magnetotelluric(MT)data.It usually causes distortion at the fundamental frequency and its odd harmonics,and may also affect other frequency bands.Although trap circuits are designed to suppress such noise in most of the modern acquisition devices,strong interferences are still found in MT data,and the power-line interference will fluctuate with the changing of load current.The fixed trap circuits often fail to deal with it.This paper proposes an alternative scheme for power-line interference removal based on frequency-domain sparse decomposition.Firstly,the fast Fourier transform of the acquired MT signal is performed.Subsequently,a redundant dictionary is designed to match with the power-line interference which is insensitive to the useful signal.Power-line interference is separated by using the dictionary and a signal reconstruction algorithm of compressive sensing called improved orthogonal matching pursuit(IOMP).Finally,the frequency domain data are switched back to the time domain by the inverse fast Fourier transform.Simulation experiments and real data examples from Lu-Zong ore district illustrate that this scheme can effectively suppress the power-line interference and significantly improve data quality.Compared with time domain sparse decomposition,this scheme takes less time consumption and acquires better results.

A hybrid finite-element and integral-equation method for forward modeling of 3D controlled-source electromagnetic induction

We have developed a hybrid solver that combines the finite-element and integralequation method for 3D CSEM modeling based on unstructured meshes. To avoid the source singularity, the secondary field is used in the modeling framework. The primary electromagnetic field from an electric dipole source in a layered medium is calculated based on the magnetic vector potential method. The inhomogeneities of the computational region are discretized by a vector-based finite-element mesh with boundaries at finite distance from the inhomogeneities by using the dyadic Green's function, reducing the truncation boundary effect and the solution region. The electric and magnetic Green's function is used in data postprocessing to reduce the numerical errors owing to inaccurate gradients because of unstructured meshes; thus, the electromagnetic field is more accurately calculated. Finally, the proposed algorithm is applied to a block and a disc model, and we assess the topography effect on the field components.

Magnetotelluric signal-noise separation method based on SVM–CEEMDWT

To better retain useful weak low-frequency magnetotelluric(MT)signals with strong interference during MT data processing,we propose a SVM-CEEMDWT based MT data signal-noise separation method,which extracts the weak MT signal affected by strong interference.First,the approximate entropy,fuzzy entropy,sample entropy,and Lempel-Ziv(LZ)complexity are extracted from the magnetotelluric data.Then,four robust parameters are used as the inputs to the support vector machine(SVM)to train the sample library and build a model based on the different complexity of signals.Based on this model,we can only consider time series with strong interference when using the complementary ensemble empirical mode decomposition(CEEMD)and wavelet threshold(WT)for noise suppression.Simulation results suggest that the SVM based on the robust parameters can distinguish the time periods with strong interference well before noise suppression.Compared with the CEEMD WT,the proposed SVM-CEEMDWT method retains more low-frequency low-variability information,and the apparent resistivity curve is smoother and more continuous.Moreover,the results better reflect the deep electrical structure in the field.

基于Python的含体积型缺陷管道剩余强度评价

针对油气管道因腐蚀等因素造成剩余强度减弱的问题,深入研究了国标SY/T 6477-2017《含缺陷油气管道剩余强度评价方法》。为简化含体积型缺陷管道剩余强度评价过程,依据该标准,以JetBrains PyCharm Community Edition作为开发工具,用Python编程语言,采用GUI数据库中的Tkinter模块开发了剩余强度评价软件。

基于CFD的某商用车冷却性能提升研究

针对某型商用车冷却性能提升问题,运用数值模拟仿真方法对发动机舱内的流场和温度场进行分析研究。根据流场与温度场的仿真结果,确定机舱中热回流的位置以及形成发动机舱内的高温热害的原因,结合整个发动机舱布局,提出了加厚水箱、优化机舱流道以及在车架内和散热器左前方加挡风板的改进方案,并加以匹配分析得到最优组合方案。仿真结果表明:加厚水箱、发动机后移以及在车架内加挡板的组合方案有效减轻热回流现象,其散热器冷却常数K值较原机降低10.4℃,有效改善发动机舱散热环境。

A new approach for calculating the apparent resistivity tensor

The apparent resistivity tensor pB is an electromagnetic transfer function,which can be used to analyze and explain the underground electrical structure.Conventional method for obtaining the parameter requires controlled sources and can be easy to be disturbed by cultural noises.We present a new method for calculating the apparent resistivity tensor,the current density is first obtained by measuring the curl operator of the magnetic field on the Earth's surface.This approach is independent of the assumption of a plane wave,and may be used irrespective of source types and field areas.We derived the analytical expressions of the apparent resistivity tensor based on synthetic horizontally layered models with a vertical magnetic dipole source.We then calculate the responses of Pb through numerical modeling examples using both natural sources and controlled sources.Compared to traditional apparent resistivity definitions,our apparent resistivity tensor has the same amplitude value but with more sensitive phases in the far zone,and shows few distortions in the transition zone.And in the near-field zone,it is closer to the resistivity distribution under the ground.The simulation results have demonstrated the effectiveness of the proposed method for calculating the apparent resistivity tensor.

Groundwater resources survey of tongchuan city using the audio magnetotelluric method

The development of Tongchuan City,Shaanxi Province,located in the northwestern region of China,is restricted by water resources.The direct current resistivity and induced polarization sounding methods are typically applied in finding urban groundwater.These methods,however,are not effective due to their complicated topography and geological conditions.The application practice shows that the audio magnetotelluric(AMT)method has a large depth of exploration,high work effi ciency,and high lateral resolution.To investigate the distribution of groundwater resources,we deployed three audio-frequency magnetotelluric profiles in the city area.The impedance tensor information of AMT data is obtained using SSMT2000.AMT data dimension analysis reveals that the two-dimensional structural features of the observation area are obvious.The main structure of the observation area is about 45°northeast,as indicated by structural trend analysis.A shallow two-dimensional electrical profile of 1 km in Tongchuan City is obtained by two-dimensional nonlinear conjugate gradient inversion.Finally,combined with regional geological information,the geological structure characteristics reflected by the electrical profile were obtained along with the detailed characteristics of water-rich structures in the area.The infl uence of the structure on the groundwater distribution was analyzed,and the water-rich areas were identifi ed.This work contributes to the prospective development of Tongchuan City.

基于小波细节信息的重力源参数估算

小波多尺度分析方法在位场数据处理领域得到了广泛关注.目前,人们对利用该方法分离位场数据所得到的小波细节横向边缘信息认知不够深入,有必要做进一步探究.本文首先采用小波多尺度位场分离方法分离出区域和局部重力异常,然后利用haar小波变换HVD模法对局部异常信息进行多尺度分析,将所得到的小波细节信息进行水平、垂直和对角线方向分解,探测出局部异常体的横向边缘特征,并利用频谱分析方法估测出场源深度.最后,通过理论模型和南非Witwatersrand Basin航空实测重力数据进行分析,表明小波多尺度分析方法不仅能很好地实现位场分离、近似提取异常体场源深度,还可以利用小波细节信息有效地分辨出局部异常体的横向边缘特征,提高其识别精度.

基于Android平台的广域电磁接收机采集监控软件研究与实现

现有广域电磁接收机采集监控设备便携性、人机交互、续航能力不佳给野外数据采集带来一定困难,为此可借助Android智能手机在普及率高、用户基础好、便携性佳、计算能力相对较强、人机交互好、续航能力佳、随时随地的无线通信能力等方面的优势实现监控设备朝轻量化和移动化发展,而实现该目标的关键在于设计一款针对通用Android平台智能手机的采集监控软件.该文在搭载Android系统的通用智能手机上设计开发了集Wi Fi(Wireless Fidelity)通信、多线程并行、实时监控、数据可视化、SQLite存储、文件存储于一体的应用程序,在其中可设置或接入WLAN(Wireless Local Area Network)无线局域网,设置测点、测线、采集周期、工作次数等采集任务参数,实时监控多台电磁接收机的运行状态,实现处理数据的双对数坐标显示等.经过试验表明该监控软件功能高效、便携性好,能极大方便工作人员的野外数据采集,具有一定的实际应用价值.