Fractals,fault-gouge,and friction

The particle-size distribution of a natural fault-gouge has been determined over the range from 5 m to 40 cm. The gouge is self-similar over the range from 5 m to 1 cm having a fractal dimension of 2.60±0.11. The lower and upper fractal limits were also determined. The lower fractal limit occurs at a dimension of about 1–10 m where mineral cleavage and intergranular porosity dominate the cataclasis. The upper fractal limit occurs at particle sizes on the order of 1 cm where the scaled particle density decreases abruptly by a factor of about three. By analogy to soil-mechanics shear box tests and laboratory rock friction experiments, it is argued that the upper fractal limit of the gouge determines the characteristic displacement parameter in stick-slip friction models. A characteristic displacement on the order of 1 cm is consistent with estimates based on numerical simulations of faulting.     

Fractals in Karst

The analysis of cave survey data is used to establish that cave length exhibits fractal (self-similar) behaviour, with dimensions in the range 1–1·5, over a range of measurement resolutions from 1 to 100 m. It is suggested that fractal dimensions, together with their range of applicability, will prove to be useful parameters for the study of caves.     

Modelling of magnetic data for scaling geology

Interpretation of magnetic data can be carried out either in the space or frequency domain. The interpretation in the frequency domain is computationally convenient because convolution becomes multiplication. The frequency domain approach assumes that the magnetic sources distribution has a random and uncorrelated distribution. This approach is modified to include random and fractal distribution of sources on the basis of borehole data. The physical properties of the rocks exhibit scaling behaviour which can be defined as P(k) = Ak^?β, where P(k) is the power spectrum as a function of wave number (k), and A and β are the constant and scaling exponent, respectively. A white noise distribution corresponds to β = 0. The high resolution methods of power spectral estimation e.g. maximum entropy method and multi‐taper method produce smooth spectra. Therefore, estimation of scaling exponents is more reliable. The values of β are found to be related to the lithology and heterogeneities in the crust. The modelling of magnetic data for scaling distribution of sources leads to an improved method of interpreting the magnetic data known as the scaling spectral method. The method has found applicability in estimating the basement depth, Curie depth and filtering of magnetic data.     

黄海地质与地球物理特征研究进展

本文介绍了近几年对黄海地质特征、地球物理特征研究所取得的成果，北黄海盆地已发现工业性油流，南黄海北部盆地和中间隆起取得巨大进展，是油气有利勘探区；黄海的断裂带及块体结合带制约着黄海油气藏形成，对其研究对黄海油气勘探研究有着重要指导作用，分析认为对黄海的研究还需进一步加强地质与地球物理手段综合研究。     

Magnetic anisotropy of rocks and its application in geology and geophysics

Magnetic anisotropy in sedimentary rocks is controlled by the processes of deposition and compaction, in volcanic rocks by the lava flow and in metamorphic and plutonic rocks by ductile deformation and mimetic crystallization. In massive ore it is due to processes associated with emplacement and consolidation of an ore body as well as to ductile deformation. Hence, it can be used as a tool of structural analysis for almost all rock types. Morcover, it can influence considerably the orientation of the remanent magnetization vector as well as the configuration of a magnetic anomaly over a magnetized body. For these reasons it should be investigated in palaeomagnetism and applied geophysics as well.     

Lithosphere types in North China: Evidence from geology and geophysics

Deep-seated materials from lithosphere are the ba- sic parameters and the foundation for geodynamic and continental dynamic studies. Division of lithosphere types and their deep-seated materials and structure can provide important evidence in interpreting the com- plex phenomena derived from the processes of forma- tion and evolution of continents, in evaluating the mineral resource potential, in predicting geological disasters and in the research of the continental dy- namic process. Huge lit…     

The geology and geophysics of the ambrym caldera,New Hebrides

Ambrym Island has an unusually large, well-preserved basaltic caldera 13 km across. The caldera occurs in the central region of an early broad composite cone, which formed a north-south line with three smailer volcanoes. Alter the caldera was formed volcanism occurred within it and along fissure lines running nearly east-west. Two volcanic cones are active almost continuously and historic fissure cruptions have been recorded. The caldera formed by quiet subsidence, or by subsidence accompanied by eruption of scoria lappili similar to that erupted prior and subsequent to caldera formation. The collapse was at least 600 metres and radiocarbon dating suggests it took place less than 2000 years ago. The caldera is detined by gravity anomalies 10 to 14 milligals lower than those at its rim suggesting predominantly ash infilling. Aeromagnetic anomalies show a prominent. nearly east-west lineation, with normally magnetised bipole anomalies over the centre of the caldera and over fissure lines east of it. The source of the present volcanic activity is believed to be located along dyke fissures, with a perched magma chamber beneath the caldera. The geophysical evidence on Ambrym, together with that of regional east trending magnetic anomalies and recent bathymetric results, suggests that the volcanic activity is localised by the intersection of an east-west fracture zone with the axis of the New Hebrides island are.     

Reconnaissance geophysics and geology of the Pinacate craters,Sonora, Mexico

The Pinacate volcanic field of northwest Sonora, Mexico contains eleven tuff-rimmed explosion craters as well as hundreds of cinder cones. A multiphase eruptive and collapse history for each of the craters is evidenced by: cinder cones exposed in cross-section in crater rims, rim-breaking cinder cones, major eccentric vents, erosion hiatuses between tuff deposition, and coalescing craters exhibiting differeng degrees of erosion. Basaltic intrusions occurred along ring fractures and in the center of at least one crater. Magnetic surveys indicate that explosion craters have tuffaceous feeder vents whereas cinder cones have basaltic, highly magnetic plugs. Computer models illustrate that magnetic terrain effects can contribute to anomalies observed associated with craters, and need to be considered where magnetic surveys include irregularities such as rims or peaks.     

Age, geology, geophysics, and geochemistry of Mahukona Volcano, Hawai`i

The size, shape, and magmatic history of the most recently discovered shield volcano in the Hawaiian Islands, Mahukona, have been controversial. Mahukona corresponds to what was thought to be a gap in the paired sequence (Loa and Kea trends) of younger Hawaiian volcanoes (<4?Ma). Here, we present the results of marine expeditions to Mahukona where new bathymetry, sidescan sonar, gravity data, and lava samples were collected to address these controversies. Modeling of bathymetric and gravity data indicate that Mahukona is one of the smallest Hawaiian volcanoes (～6,000?km³) and that its magmatic system was not focused in a long-lived central reservoir like most other Hawaiian volcanoes. This lack of a long-lived magmatic reservoir is reflected by the absence of a central residual gravity high and the random distribution of cones on Mahukona Volcano. Our reconstructed subsidence history for Mahukona suggests it grew to at least ～270?m below sea level but probably did not form an island. New ⁴⁰Ar–³⁹Ar plateau ages range from 350 to 654?ka providing temporal constraints for Mahukona’s post-shield and shield stages of volcanism, which ended prematurely. Mahukona post-shield lavas have high ³He/⁴He ratios (16–21?Ra), which have not been observed in post-shield lavas from other Hawaiian volcanoes. Lava compositions range widely at Mahukona, including Pb isotopic values that straddle the boundary between Kea and Loa sequences of volcanoes. The compositional diversity of Mahukona lavas may be related to its relatively small size (less extensive melting) and the absence of a central magma reservoir where magmas would have been homogenized.     

Mapping of magnetic basement in Central India from aeromagnetic data for scaling geology

The Central Indian region has a complex geology covering the Godavari Graben, the Bastar Craton (including the Chhattisgarh Basin), the Eastern Ghat Mobile Belt, the Mahanadi Graben and some part of the Deccan Trap, the northern Singhbhum Orogen and the eastern Dharwar Craton. The region is well covered by reconnaissance‐scale aeromagnetic data, analysed for the estimation of basement and shallow anomalous magnetic sources depth using scaling spectral method. The shallow magnetic anomalies are found to vary from 1 to 3 km, whereas magnetic basement depth values are found to vary from 2 to 7 km. The shallowest basement depth of 2 km corresponds to the Kanker granites, a part of the Bastar Craton, whereas the deepest basement depth of 7 km is for the Godavari Basin and the southeastern part of the Eastern Ghat Mobile Belt near the Parvatipuram Bobbili fault. The estimated basement depth values correlate well with the values found from earlier geophysical studies. The earlier geophysical studies are limited to few tectonic units, whereas our estimation provides detailed magnetic basement mapping in the region. The magnetic basement and shallow depth values in the region indicate complex tectonic, heterogeneity, and intrusive bodies at different depths, which can be attributed to different thermo‐tectonic processes since Precambrian.     

江苏及邻区地震时序的多重分形特征及其预报意义

近年来,大震前地震活动标度不变性的特征变化研究引起了人们的极大关注。然而,由于不同地区的地震活动特点不同,要获得这种特征变化并不容易。本文首先介绍了这方面研究的重要进展,这些进展对地震预报和地震活动性的研究者来说有很大的参考价值。其次,讨论了几种标度不变性方法（局域标度特性、多重分形谱、Hurst指数分析和分形维数方法）的优缺点。最后,提出了有关该研究的建设性建议：当人们试图通过标度不变性方法获取大震前的前兆信息或地震活动分形特征时,需要考虑方法的优缺点以提高地震预报效能,否则地震预报效能会大大降低。     

A probabilistic procedure to assess the uncertainty of fractal dimensions from measurements

In order to assess the degree of uncertainty of fractal dimensionality, a procedure is given which provides a cumulative probability measure of uncertainty of fractal dimensionality in terms of assessments of range and most likely value. The procedure allows for a variation of the model proposed (i.e., variability of the parameters involved in the fractal relation) and leads to a relevant estimate of the uncertainty. The procedure is simple to apply and useful in providing a statistically valid comparison of results.As an illustration, the procedure was used on the fractal dimensions of faults measured from shear zones of different scale magnitudes. Results suggest that these shear zones are indeed quantitatively similar with a fractal dimension around 1.5. It is also shown that the range of uncertainty of the fractal dimensionality (90% likelihood range) is sensitive to the amount of data used to calculate the fractal dimension of the faults.     

SQUID及在地球物理中的应用

SQUID(Superconducting Quantum Interference Device)技术(特别是高温SQUID)的发展，为地球物理探测技术的发展提供了巨大潜力，基于SQUID技术开发的地球物理探测系统不仅具有精度高、分辨率高的优点，而且仪器系统轻便，在野外实验和应用取得了巨大的进展，本文将近年SQUID技术应用于地球物理取得的进展进行了简要的总结，并阐述它了在地球物理勘探领域的广阔应用。     

地球物理科学中两个有趣的问题

1、关于大气O3层的形成,除了主过程——Chapman过程外,还可能另有一个过程,特别在两极地区,是为带电微粒的电化学过程.2、依照“斥力论”,地球大气外绷,应当类似于慧星,在夜的一侧,拖着一条长长的尾巴.     

2001年地球物理学的一些进展

简要回顾了2001年地球物理学的一些进展。指出在用地球系统科学研究整个地球的结构、演化和动力学过程中，地球物理学作为地球科学中主要提供地球内部信息和资料的学科，将成为地球系统科学研究的一个重要内容。讨论了现在的地球和空间科学研究以及环境监到等地球物理技术在反恐怖活动以及在国家军事方面的重要意义及应用。在21世纪能源危机日益严重的情况下，中国急需进行油气资源的二次创业，而天然气水合物研究是能源研究的一个新方向。     

岩石磁学与古地磁实验室简介

近年来，中国科学院地质与地球物理研究所岩石磁学与古地磁学实验室始终以实验、观测和理论“三位一体”的研究思路为宗旨，提出了以先进的硬件设备、完善的测试环境和创新的实验方法为依托体系的现代实验室建设理念，富有创意地发展了一些实验技术和实验方法，建立了国际水平的实验条件和实验能力．良好的研究环境和富有开拓的研究思路，吸引了包括欧美国家在内的国际知名学者来实验室开展合作研究．近年来每年都有一批实验数据在Nature，JGR(Journal of Geophysical Research)，EPSL(Earth P1anet Sciences Letter)和中国科学、地球物理学报等国内外学术期刊发表．该实验室已逐步成为岩石磁学与古地磁学领域国内外研究中心之一，大大地提升了我国在该领域研究的国际地位．     

THE WEST COAST OF BRITAIN: STATISTICAL SELF-SIMILARITY VS. CHARACTERISTIC SCALES IN THE LANDSCAPE

Mandelbrot (Science, 1967, 156, 636–638) used the west coast of Britain as an example of a naturally occurring statistically self-similar fractal. Evidence from this study indicates that the west coast of Britain is not statistically self-similar over the range of scale of measurement, and that complexity reaches maxima at characteristic scales related to identifiable features on the coastline. A fractal analysis is conducted using the divider method, and although the resulting log–log plot of measured length against steplength appears linear, statistical tests for linearity strongly suggest that the coastline is not statistically self-similar. An angle measure technique (AMT) developed by the author to examine changes in line complexity with scale, shows that within the range of scale of measurement there are two peaks in complexity for the west coast of Britain, suggesting that two processes acting at different scales have influenced coastal development. The AMT is also used to identify differences in complexity between northern and southern sections of the coastline. Additionally, high r² values associated with regressions of log L(G) against log G are shown to be insufficient evidence of statistical self-similarity, and apparently linear segments (fractal elements) often found in Richardson plots may contain systematic curvature revealed only by more rigorous tests for non-linearity.     

A scale‐invariant property of the water retention curve in weakly heterogeneous vadose zones

Abrupt changes of hydraulic properties in a vadose zone are modelled within a stochastic framework, which regards the saturated conductivity and parameters related to the distribution of soil pores as stationary, log‐normally distributed, random space functions. As a consequence, flow variables become random fields, and we aim at deriving an effective Richards equation. To obtain the latter, we adopt a perturbation expansion truncated at the first order (weakly heterogeneous media), which leads to the effective hydraulic conductivity and water retention curves. Overall, the effective properties are scale dependent. However, within the proposed framework, we demonstrate that the inflection point of the laboratory scale retention curve is not affected by the heterogeneity of the vadose zone. Finally, to illustrate the quantitative implications of our results, we consider a monitoring experiment at field scale, and we show how our approach leads to an effective water retention curve, which differs significantly from that which would be obtained without accounting for the above scale‐invariance property.     

Invariance and scaling properties in the distributions of contributing area and energy in drainage basins

The cumulative probability distributions for stream order, stream length, contributing area, and energy dissipation per unit length of channel are derived, for an ordered drainage system, from Horton's laws of network composition. It is shown how these distributions can be related to the fractal nature of single rivers and river networks. Finally, it is shown that the structure proposed here for these probability distributions is able to fit the observed frequency distributions, and their deviations from straight lines in a log-log plot.