Geophysical signatures over and around the northern segment of the 85°E Ridge,Mahanadi offshore,Eastern Continental Margin of India: Tectonic implications

The nature and origin of the subsurface 85°E Ridge in the Bay of Bengal has remained enigmatic till date despite several theories proposed by earlier researchers. We reinterpreted the recently acquired high quality multichannel seismic reflection data over the northern segment of the ridge that traverses through the Mahanadi offshore, Eastern Continental Margin of India and mapped the ridge boundary and its northward continuity. The ridge is characterized by complex topography, multilayer composition, intrusive bodies and discrete nature of underlying crust. The ridge is associated with large amplitude negative magnetic and gravity anomalies. The negative gravity response across the ridge is probably due to emplacement of relatively low density material as well as ∼2–3 km flexure of the Moho. The observed broad shelf margin basin gravity anomaly in the northern Mahanadi offshore is due to the amalgamation of the 85°E Ridge material with that of continental and oceanic crust. The negative magnetic anomaly signature over the ridge indicates its evolution in the southern hemisphere when the Earth’s magnetic field was normally polarized. The presence of ∼5 s TWT thick sediments over the acoustic basement west of the ridge indicates that the underlying crust is relatively old, Early Cretaceous age.The present study indicates that the probable palaeo-location of Elan Bank is not between the Krishna–Godavari and Mahanadi offshores, but north of Mahanadi. Further, the study suggests that the northern segment of the 85°E Ridge may have emplaced along a pseudo fault during the Mid Cretaceous due to Kerguelen mantle plume activity. The shallow basement east of the ridge may have formed due to the later movement of the microcontinents Elan Bank and Southern Kerguelen Plateau along with the Antarctica plate.     

用岩芯模拟测试参数做模型正演预测储层油、气、水边界

利用地震资料进行AVO油气检测,需要提供准确的储层岩石物性参数．通过对准噶尔盆地西部储层岩样实验室测定,得出合不同流体岩石在不同温度、压力下纵横波速度、速度比、泊松比的变化规律及差异．根据其差异性,用Zoeppritz方程做模型正演,以确定目的层有无AVO响应,以便对地震剖面做针对性的特殊处理．实际应用结果表明,用实验室测试的岩石物性参数做模型正演,可提高AVO检测的准确性,为用地震资料结合实验室岩芯测试参数预测地层油、气、水边界提供了有效手段．     

Particle spectra from acceleration at forward and reverse shocks of young Type Ia Supernova Remnants

We study cosmic-ray acceleration in young Type Ia Supernova Remnants (SNRs) by means of test-particle diffusive shock acceleration theory and 1-D hydrodynamical simulations of their evolution. In addition to acceleration at the forward shock, we explore the particle acceleration at the reverse shock in the presence of a possible substantial magnetic field, and consequently the impact of this acceleration on the particle spectra in the remnant. We investigate the time evolution of the spectra for various time-dependent profiles of the magnetic field in the shocked region of the remnant. We test a possible influence on particle spectra of the Alfvénic drift of scattering centers in the precursor regions of the shocks. In addition, we study the radiation spectra and morphology in a broad band from radio to gamma-rays. It is demonstrated that the reverse shock contribution to the cosmic-ray particle population of young Type Ia SNRs may be significant, modifying the spatial distribution of particles and noticeably affecting the volume-integrated particle spectra in young SNRs. In particular spectral structures may arise in test-particle calculations that are often discussed as signatures of non-linear cosmic-ray modification of shocks. Therefore, the spectrum and morphology of emission, and their time evolution, differ from pure forward-shock solutions.     

盈江“3·10”地震诱发地质灾害隐患及防护对策

盈江5.8级地震引发地质灾害,分析地震对地质灾害的影响及范围、地质灾害形成条件及隐患,提出有效防护对策、灾后重建建议。     

综合地球物理方法在华南桂中海相残留盆地沉积相预测中的应用

沉积相研究是盆地隐蔽油气藏勘探中重要的研究内容之一,综合利用地球物理方法有效识别构造、岩性或沉积相差异是盆地隐蔽油气藏勘探的前提.本文基于重力、航磁、地震等综合地球物理资料,通过重磁异常正演剥离和剖面正反演拟合技术研究了华南桂中地区海相地层的密度分布特征,预测了岩相、沉积相的变化规律.研究发现,本区中、下泥盆统海相地层存在横向的岩性、岩相变化,研究区西北、东南部的台地相区重力异常高、岩石拟合密度值高;中部“X”型台地边缘相区重力异常杂乱、岩石拟合密度变化范围大;东部台沟相区重力异常低、岩石拟合密度值低.利用综合地球物理方法预测沉积相为盆地岩性圈闭油气藏和生物礁油气藏勘探提供了新的研究思路,研究成果已得到初步检验,但还有待进一步完善与实践.     

区间B样条小波有限元GPR模拟双相随机混凝土介质

基于可分离小波理论,由一维区间B样条小波尺度函数的张量积构造二维B样条小波基,并将它作为GPR波动方程求解的插值函数,通过引入转换矩阵,实现小波系数空间与雷达电磁场之间的转换.应用Galerkin算法,推导了二维区间B样条小波有限元GPR波动方程离散格式,求出了2阶1尺度与2阶2尺度BSWI尺度函数的积分值及联系系数,给出了该算法的详细求解过程.编制了BSWI的Matlab模拟程序,应用该程序对两个典型实例进行了正演,结果表明:BSWI能采用较少的单元达到与FEM相似的精度,而BSWI算法尺度提升能提高解的精度,但耗时会急剧增加.最后,将BSWI算法应用于双相随机混凝土模型,说明随机介质模型理论能灵活、有效地描述实际混凝土介质的分布,正演剖面与实测剖面特征更相符,能更真实地模拟雷达波的传播过程,可为提高GPR的探测效果和解释准确性提供理论基础.     

三维任意各向异性介质中海洋可控源电磁法正演研究

由于海底介质受沉积环境的影响,层理发育呈现明显各向异性特征.对于海洋可控源电磁法各向异性的研究以往主要局限于一维和二维模型,为更深入了解复杂情况下海底各向异性对海洋可控源电磁响应的影响规律,本文开展三维任意各向异性介质中海洋可控源电磁法正演研究.采用交错网格有限差分技术,通过对任意各向异性介质电导率张量实行体积和空间电流密度平均,完成海洋可控源电磁二次散射电场的离散化,成功实现任意各向异性介质中海洋可控源电磁正演模拟.通过对几种典型各向异性电性模型条件下海洋电磁电场多分量响应及分布特征和各向同性情况的对比分析,总结电各向异性对海洋电磁响应的影响规律和识别方法.本文算法研究及算例可为海洋可控源电磁数据精细化处理解释提供技术支撑.     

Application of the 3D magnetotelluric inversion code in a geologically complex area

The WSINV3DMT code makes the implementation of 3D inversion of magnetotelluric data feasible using a single PC. Audio‐magnetotelluric data were collected along two profiles in a Cu‐Ni mining area in Xinjiang, China, where the apparent resistivity and phase curves, the phase tensors and the magnetic induction vectors indicate a complex 3D conductivity structure. 3D inversions were carried out to reveal the electrical structure of the area. The final 3D model is selected from the inversion results using different initial Lagrange values and steps. The relatively low root‐mean‐square (rms) misfit and model norm indicate a reliable electrical model. The final model includes four types of low resistivity areas, the first ones coincide with the known location of an orebody and further forward modelling indicates that they are not in full connectivity to form a low resistivity zone. The second ones are not controlled by magnetotelluric sites and embody little information of the observed data, they are considered as tedious structures. The third one is near to the regional Kangguer fault and should be treated carefully considering the effect of the fault. The last ones are isolated and existing at a limited level as the first ones, they should be paid more attention to.     

一维电阻率各向异性对海洋可控源电磁响应的影响研究

地下介质的电阻率常常表现为各向异性,海底裂隙地层和层状沉积序列可能形成宏观电阻率各向异性.在解释海洋电磁资料时,电阻率各向异性的影响不应该被忽略,否则可能会得到错误的海底地电模型.作者编写了电阻率任意各向异性一维层状介质海洋可控源电磁场计算程序,计算了电阻率各向异性层状模型的海洋可控源电磁响应,讨论了覆盖层和高阻储层分别具有电阻率各向异性时的电磁场响应特征.     

电离层-空气层-地球介质耦合下大尺度大功率可控源电磁波响应特征研究

电离层-空气层-地球介质（我们称为“地-电离层”模式）耦合下大功率可控源电磁波的研究在国内外较少.近年来,有学者做了相关的数值模拟,但没有考虑空气中位移电流的影响.我们根据研究对象和问题建立地质模型和相应的数学模型,采用R函数法进行“地-电离层”模式水平电缆接地偶极源的电磁波场强公式推导,同时考虑电离层和空气中位移电流的影响.在验证方法可靠的前提下,进行了数值计算.探讨了“地-电离层”模式大功率可控源电磁波的响应特征.数值计算结果表明,由于电离层和空气层中位移电流的影响,“地-电离层”模式大功率可控源电磁波的特征与地球半空间可控源电磁波的特征有很大的不同,体现在前者除了有近场、远场外,还存在由于电离层影响下场强衰减变小的波导场.并随着收发距增大和频率的增高,出现了电场和磁场方向图的变化.