郯庐断裂带南段构造演化与邻区成矿作用——从年代学资料得到的启示

郯庐断裂带为我国东部北北东—北东向岩石圈深大断裂带。在其南段的邻区,分布有胶东金矿区、鲁西铁金矿区以及长江中下游的铁铜(金)成矿带和苏北油气田等矿产。从已获得大量测年资料分析,可将构造—岩浆—成矿事件分为3个阶段:1)早期(800～550 Ma):自元古宙泛古陆裂解和随之而来的加里东期古地震和局部海西期喷流作用,证实地壳运动早已拉开了它的构造活动序幕,此阶段继承和构建了华北克拉通岩石圈先存的构造薄弱带,从成矿作用而论,此阶段可称为成矿预备场地;2)主期(1 80～110 Ma):在三叠纪期间,扬子板块和华北板块陆—陆碰撞和中生代西太平洋板块向欧亚板块俯冲等,造就了现今郯庐断裂与分支断裂的构造格架。其中主峰形成时间为140～120 Ma±,在这个阶段广泛有钙碱性系列、富钾高锶钙碱系列、碱性系列岩浆和后期成矿热液,沿着有利构造空间剧烈活动和成矿就位。本区壳幔混熔型和壳源同熔型花岗岩,是地壳减薄和下地壳拆沉、底侵的产物,而不是单一的构造运动的结果。此阶段可称为断裂构造—岩浆活动—成矿作用的鼎盛期;3)晚期(60Ma～现代):沿东西向与北北东向(或北东向)断裂交汇处,存在橄榄玄武岩喷侵,为石油和天然气的形成提供了热源和物源,此期可称其为构造—岩浆活动的衰变期。     

浅谈地震灾害符号体系构建的理论框架

地震灾害符号的研究已经成为地震应急工作的一项重要内容,本文借助于符号学及传播学的方法论,在分析地震灾害符号的符号学内涵、使用人群和传播内容的基础上,探讨了地震灾害符号体系的特点及构建原则。地震本身的特殊性和破坏性决定了地震灾害符号体系的特殊性和时间性,本文在遵循实用性、主次性及概括性三个原则的前提下,提出了一套地震灾害符号体系构建的理论框架,可为地震灾害符号体系的构建和深入研究提供参考。     

Rate and historical change of direct recharge from precipitation constrained by unsaturated zone profiles of chloride and oxygen‐18 in dry river bed of North China Plain

Quantifying of direct recharge derived from precipitation is crucial for assessing sustainability of well‐irrigated agriculture. In the North China Plain, the land use is dominated by groundwater‐irrigated farmland where the direct recharge derived from precipitation and irrigation. To characterize the mean rate and historical variance of direct recharge derived from precipitation, unsaturated zone profiles of chloride and δ¹⁸O in the dry river bed of the Beiyishui River were employed. The results show that archival time scale of the profile covers the duration from 1980 to 2002 (corresponding to depths from 5 to 2 m) which is indicated by matching the δ¹⁸O peaks in the isotope profile with the aridity indexes gained by instrumental records of annual precipitation and annual potential evaporation. Using the chloride mass balance method, the mean rate of the direct recharge corresponding to the archival time scale is estimated to be 3·8 ± 0·8 mm year^?1, which accounts for about 0·7% of the long‐term average annual precipitation. Further, the direct recharge rates vary from 2·1 to 6·8 mm year^?1 since 1980. Despite the subhumid climate, the estimate of recharge rates is in line with other findings in semiarid regions. The low rate of direct recharge is considered as a result of the relative dry climate in recent decades. In dry river bed, unsaturated zone profiles of chloride and δ¹⁸O combined with instrumental records could offer valuable information about the direct recharge derived from precipitation during droughts. Copyright © 2011 John Wiley & Sons, Ltd.     

Nonlinear inversion of electrical resistivity imaging using pruning Bayesian neural networks

Conventional artificial neural networks used to solve electrical resistivity imaging (ERI) inversion problem suffer from overfitting and local minima. To solve these problems, we propose to use a pruning Bayesian neural network (PBNN) nonlinear inversion method and a sample design method based on the K-medoids clustering algorithm. In the sample design method, the training samples of the neural network are designed according to the prior information provided by the K-medoids clustering results; thus, the training process of the neural network is well guided. The proposed PBNN, based on Bayesian regularization, is used to select the hidden layer structure by assessing the effect of each hidden neuron to the inversion results. Then, the hyperparameter α _k , which is based on the generalized mean, is chosen to guide the pruning process according to the prior distribution of the training samples under the small-sample condition. The proposed algorithm is more efficient than other common adaptive regularization methods in geophysics. The inversion of synthetic data and field data suggests that the proposed method suppresses the noise in the neural network training stage and enhances the generalization. The inversion results with the proposed method are better than those of the BPNN, RBFNN, and RRBFNN inversion methods as well as the conventional least squares inversion.     

Implementation of Elastic Prestack Reverse-Time Migration Using an Efficient Finite-Difference Scheme

Elastic reverse-time migration (RTM) can reflect the underground elastic information more comprehensively than single-component Pwave migration. One of the most important requirements of elastic RTM is to solve wave equations. The imaging accuracy and efficiency of RTM depends heavily on the algorithms used for solving wave equations. In this paper, we propose an efficient staggered-grid finite-difference (SFD) scheme based on a sampling approximation method with adaptive variable difference operator lengths to implement elastic prestack RTM. Numerical dispersion analysis and wavefield extrapolation results show that the sampling approximation SFD scheme has greater accuracy than the conventional Taylor-series expansion SFD scheme. We also test the elastic RTM algorithm on theoretical models and a field data set, respectively. Experiments presented demonstrate that elastic RTM using the proposed SFD scheme can generate better images than that using the Taylor-series expansion SFD scheme, particularly for PS images. FurH. thermore, the application of adaptive variable difference operator lengths can effectively improve the computational efficiency of elastic RTM.     

Post-collisional mafic magmatism: Record of lithospheric mantle evolution in continental orogenic belt

Science China Earth Sciences - In order to better understand the role of post-collisional mafic magmatism at convergent plate boundaries in revealing the earth’s evolution, this paper has...     

基于移动平台的测震应急流动台现场监控系统的设计与实现

流动测震观测是在大地震发生以后开展的一项重要的地震应急响应工作,能够获得震区高质量的地震数据,而野外环境的复杂性对测震应急流动台的架设提出了较高的要求。本文通过对地震应急流动现场工作进行需求分析,设计并实现了一种基于IOS系统的测震应急流动台现场监控系统,能够让现场工作队员快速获取流动台数据和状态信息,有利于流动台的快速架设,提高了应急流动观测现场工作的效能。     

四川2015速度模型在九寨沟M_S7.0地震震源深度测定中的应用

利用四川2015模型,选择Msdp嵌入的几种常用定位方法对九寨沟M_S7.0地震进行重新定位,比较震源深度结果,并用PTD方法验证合适的震源深度,从而得到较为可靠的震源深度。本文最终判定九寨沟M_S7.0地震震源深度为12±2km。     

Using stable isotopes to understand seasonal and interannual dynamics in moisture sources and atmospheric circulation in precipitation

Stable isotopes in precipitation are useful tracers to strengthen understanding of climate change and hydrological processes. In this study, the moisture sources of 190 precipitation events in Beijing were analysed using the Hybrid Single‐particle Lagrangian Integrated Trajectory model, based on which we studied the relation between variations in precipitation δ¹⁸O and dynamics in moisture sources and atmospheric circulation in seasonal and interannual timescales. Categorization of 7 groups of moisture sources was performed, among which oceanic moisture sources presented lower δ¹⁸O in precipitation than continental moisture sources. The results show that seasonal variations of precipitation δ¹⁸O were caused by changes of moisture sources. In summer, moisture from proximal oceans dominated vapour transport to Beijing due to increasing monsoon strength and resulted in a relatively small variation of precipitation δ¹⁸O. At the interannual timescale, the variations of δ¹⁸O in summer precipitation were related to dynamics in oceanic moistures, showing depleted values when the contribution of oceanic moistures, especially the proportion of long‐distance oceanic moisture, was high. Further analysis indicated that changes of oceanic moisture sources were controlled by the strength of summer monsoons. These findings address the complexity of moisture sources in midlatitude monsoon areas and suggest that isotopic signals in precipitation have the potential to deduce changes in moisture sources and atmospheric circulation and can therefore serve for palaeoclimate reconstruction.     

海拉尔盆地贝尔凹陷铜体庙组-南屯组储层次生孔隙成因及意义

海拉尔盆地贝尔凹陷白垩系南屯组和铜体庙组凝灰质砂岩、凝灰质泥岩、沉凝灰岩和凝灰岩储层是该区主要产层。油气储集空间以次生孔隙为主。大量碱性矿物组合如柯绿泥石、钠板石、碳钠铝石、方沸石、绿磷石、铈褐帘石、铁绿泥石等的存在,证明发生了大规模碱性溶解和交代作用。晶屑、玻屑、长石和粘土等填隙物均发生不同程度的溶解现象。研究表明,次生孔隙是凝灰质储层大规模碱交代作用的结果,预示盆地深部存在油气储集空间并富集油气。