1945—1995年国际参考地磁场

本文回顾了国际参考地磁场(IGRF)的建立和修改过程;介绍了最新的IGRF模型,即第六代国际参考地磁场;综述了国际参考地磁场在地磁学中的应用,并指出了在使用过程中需要注意的一些问题.     

1950-1980年中国地区主磁场模型的建立及分析

本文根据丰富的地磁资料,用泰勒多项式方法推算出1950.0、1960.0、1970.0和1980.0年中国地区的主磁场模型,绘制出各个年代地磁要素的等值线图,分析研究了局部地区地磁场泰勒多项式模型的特点.     

Geomagnetic daily variations around Huanghai earthquake

The geomagnetic daily variations of vertical component, which were recorded by geomagnetic array in Jiangsu Province, are investigated with the method of multichannel Wiener filtering. The results show that the daily standard errors between raw data and the actual output of the filter for the nearest stations away from epicenter are obviously higher than ordinary level before the Huanghai earthquake, especially three days before, then returned to normal after the earthquake. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 76–79, 1991. The project was supported by the Chinese Joint Seismological Science Foundation.     

Analytical comparison of geomagnetic total field between Sino-US stations

Using observational data of geomagnetic total intensity from 13 stations in the Beijing-Tianjin region, 3 stations in the western Yunnan region of China, and 6 stations in California of U. S. A., the daily variations and their spectra of geomagnetic total intensity were analyzed and compared. The results show that the morphology, the range and spectrum of daily variations in geomagnetic total intensity are basically the same within the local extent of 100–200 km and are different in the large extent of 500 km. The latitude factor of the daily variation range of geomagnetic total intensity is about 1–2 nT/degree within the latitude extent of 25°–40°. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 83–89, 1992. This work is supported by the State Seismological Bureau and the Chinese Joint Seismological Science Foundation, and U.S. Geological Survey.     

Research on the time changes of transfer functions at Heze observatory before and after Heze earthquake of magnitude 5.9 A discussion with Qi Wang

In this paper, the coefficients of Parkinson vectora, b and the in-phase partA _r, B_r and quadrature-phase partA _i, B_i of transter functions are calculated by using two kinds of data processing methods, respectively. The results of both methods are close to each other. All these six parameters above are low in value, showing that the electric structure in Heze area is rather uniform. It seems that the anomalous changes appeared in both results, and the values of parameters decrease before and after Heze earthquake. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 113–120, 1991.     

Magnetometer array studies in India: Present status,data interpretation and assessment of numerical modelling results

Significant results from several array of magnetometers deployed in India to probe deep geoelectrical structures of the crust and the upper mantle are reviewed in this paper. Emphasis is on critical appraisal of earlier results so that the article summarizes what has been done so far and what caution is to be taken on future work. Two large-scale arrays over northwest and peninsular India during 1979–80, have been followed up with six more linear or two-dimensional arrays over different parts of the country. “Trans-Himalayan” conductor aligned along the strike of Aravalli range, delineated by arrays over northwest India, essentially represents one of the major continental induction anomalies mapped by electromagnetic methods. Efforts for quantifying the induction effects through numerical models are shown to be constrained due to the large inter-station spacing, lack of information on the regional background conductivity distribution and the non-inclusion of the frequency dependence of induction effects. A more comprehensive modelling, not biased by these factors, enables approximating the Trans-Himalayan conductor as an asymmetric domal upwarp in the middle and lower crust located between Delhi-Hardwar ridge and Moradabad fault. Numerical modelling results for southern peninsular, despite the constraints, indicate that the strong and complex induction pattern can be adequately attributed to the combination of conductors connected with triple junction between Indo-Ceylon Graben, Comorin ridge and the west coast rifting. Induction features derived from the Valsad array, operated over basalt-covered region of western India, demarcate an enhanced conducting zone beneath Plume-associated triple junction in the Gulf of Cambay, apart from characterizing the presently active seismic zone as a resistive block.     

Initiation of a reversal to uniseriality in the polymorphinid Nodocantabricus duplexmurus n. gen., n. sp.: A double-layered Foraminifera from the lower-middle Cenomanian of Cantabria,N-Spain

The new benthic foraminifer Nodocantabricus duplexmurus n. gen., n. sp. is introduced from the lower-lower middle Cenomanian of the Bielba and Altamira formations (North Cantabrian Basin, Spain). This distinctive and atypical Polymorphinidae combines primitive and advanced test characteristics. On the one hand, it fully develops uniserially arranged chambers from an initial spiral coiling, a tendency usually observed in advanced polymorphinids. On the other hand, it possesses a composite, double-layered calcitic wall, made of inner dark microgranular and outer fibro-hyaline layers, a structure seldom documented in post-Paleozoic foraminifers.In the Cretaceous, various polymorphinid groups record significant diversification periods, which taxonomic, phylogenetic and stratigraphic significances have not been evaluated yet. We here discuss the long term evolution of the family Polymorphinidae and its phylogenetic relationship(s) with the family Nodosariidae. A tendency to reversal in the chamber arrangement, from spiral to uniserial, is initiated in the Cenomanian. This evolutive inclination may later have originated a false “nodosariid” lineage, casting doubt upon the assumed monophyly of the family Nodosariidae.     

从磁异常探讨德勒诺尔铁矿构造对矿体的控制作用

德勒诺尔铁矿赋矿地层形成时代为中元古代,其后经历过多期多次构造叠加作用,变形变质作用较为复杂。成矿期后的断裂、褶皱、节理等构造十分发育,受褶皱和断裂构造的影响,矿体的空间形态和产状极其复杂,给钻探工程部署造成很大困难。本文在地面磁测数据处理、转换及构造增强的基础上,对其所蕴含的深部构造信息进行了提取和解释,初步建立起了矿区的基本构造格架,揭示了不同期次、不同方向、不同性质的构造对矿体的控制作用,较好地解决了矿体形态复杂的找矿难题,有效提高了钻探工程的见矿率。     

Geomagnetic Models and Edge Recognition of Hydrothermal Sulfide Deposits at Mid-ocean Ridges

Near-bottom magnetic prospecting is considered to be an efficient method for investigating inactive hydrothermal areas and the study of the spatial structure of hydrothermal systems. Furthermore, geophysical forward modeling is widely used to simulate the anomalous characteristics of geological bodies. To understand the magnetic and magnetic structure features of hydrothermal sulfide deposits at mid-ocean ridges, we built 3D forward models for both mafic- and ultramafic-hosted hydrothermal sulfide deposits to simulate the near-bottom magnetic field. Our modeling results showed a low amplitude magnetic anomaly above the mafic-hosted hydrothermal sulfide deposits, and a high amplitude magnetic anomaly above the ultramafic-hosted deposits. These features allow us to identify and classify the host rocks of hydrothermal sulfide deposits. Moreover, we can recognize the edge of the magnetic anomalies using the intensity of the spatial differential vector method, considering variables such as the width of the alteration zone, the height of the observation platform, and the magnetic inclination and declination. Therefore, we propose the intensity of the spatial differential vector method as an effective approach to define the boundaries of hydrothermal sulfide deposits.