多分形断层模型与地震序列研究

本文提出形成地震序列的多分形断层模型并利用分形分维理论讨论该模型及其序列。给出本模型的震级—频度关系、余震序列中强余震预报公式和多分维D_q—q关系式,探讨了利用多分维预报地震的有效性。     

地震主压应力轴分布的分形特征研究

本文通过对全国许多地区大量的小震及中、强地震主压应力轴分布情况的详细研究，发现地震主压应力轴的分布具有分形结构特征，并满足幂函数关系式ｌｇＮ＝ａ＋ｂＪ，其特征值ｂ与分数维大致成反比，无标度区约为２°－８°。中强以上地震的前震序列的地震主压应力轴分布的特征值似乎明显比小震群活动的地震主压应力轴分布的特征值大。     

地震能量空间分布局域标度特性的初步研究

本文利用计算机数值模拟数据及大同地区三次中强地震前后的地震记录资料，在空间能量分布“漫化”的基础上，通过多重分形方法着重对能量空间分布的局域标度性质及可能的震兆信息进行研究。结果表明能量分布普遍地表现出多标度分形特性，但相同ｑ值Ｄｑ的时间变化或Ｄｑ￣ｑ谱形态变化不明显。中强地震前标度指数谱ｆ（α）￣α曲线由两端大体对称或右端略低变为左端明显下降，同时α及ｆ（α）数值分布范围扩展、顶点右移。计算机模     

地震序列的一个自相似扩展模式

本文引入地震序列的一种自扩展模式,其地震序列的发生由地震断层的不同尺度的闭锁段相继破裂而发生,同时给出了以力学参数和几何参数定标的断层的自相似破裂机制,用以解决地震断层的分形特征及破裂的慢化过程。     

地震分布多重分形特征的中期预报意义探讨

讨论了地球岩石圈的自组织临界状戍 地震发生的非局域性与多重标度分形度统计特征。研究了地震多重分形性质的计算方法及其应用于地震预报的前景 。     

地震分形与地震预报

本文认为,分维及无标度区是地震分形自组织两个重要特征参数。讨论了两个层次关联维特征及关联维 D_2计算的基本限制。初步探索了强震序列生长结构与分形原理间关系。提出地震分维函数与地震时序分布律新的研究方法及课题。分析了分维随时间变化特征及其在地震预报上的应用。     

板内地震复发间隔对断层长度的标度关系研究及应用探索

虽然关于一些重要参数值仍然存在显著的不确定性，地学家们一致认为断层分布遵从幂律标度关系。本文我们把这些标度关系和地震分布的幂律标度关系结合起来获得了区域板内地震复发间隔对断层长度的标度关系式，再对其进行局部校准进而得到某一具体小地方的地震危险估计方法。小断层（未跨越孕震层与断４层）的标度资料表明地震复发间隔和断层长度的负幂成比例变化。由于最近认识到了大震标度中参数的不确定性，对于大断层（跨越孕震层的断层），其地震复发间隔是和断层长度的负幂还是和正幂成比例变化的问题是不确定的，这个问题对地震危险估计是至关重要的。     

地震序列自仿射分形及自相似分形的计算与比较

本用标准偏差法和标度变换法，计算了云南省五个地震区带上１９６５－１９９５年间地震序列的自仿射分形的分维值Ｄ△ｔ（地震时间间隔序列自仿射分形）ＤＭ－ｔ（地震震级一时间序列自仿射分形）及自相似分形的分维值Ｄ０（地震时间分布自相似分形）得到了相应的时间变化曲线，ＤＭ－ｔ～ｔ，Ｄ△ｔ～ｔ和Ｄ０～ｔ。通过相互比较发现，其中ＤＭ－ｔ的随时间变化在中强地震前的反应最为敏感。     

地壳形变与分形

众所周知,地震的频度-震级统计关系满足古登堡-里克特关系式。易知,这一关系是分形的,分维数D=1.8～2.0。既然每条断层都有其特征地震这一观点已被普遍接受,那么断层的频数-尺度统计关系也将是分形的。有限的野外研究表明,断层的出露部分是D≈1.6的二维分形(地震和断层的分维数并不要求一定相等,因为地震的复发时间亦具有依赖于标度的幂律关系)。断块在很宽的尺度范围内具有D≈2.5的分形频数-尺度关系。关于构造形变的一个模型就是碎裂,这样一个标度不变的模型似乎与上述讨论的分形关系是一致的。地震活动性具有许多“自组织临界现象”的显著特性,能量(应变)被持续不断地施加于地壳上,又以离散事件的形式(地震)被释放掉,而这些离散的事件具有分形的频数-尺度分布。这样,认为大陆地壳的所有地方均处于这样一种临界状态似乎是有道理的(类似于与完全塑性有关的临界应力),其证据来源于板内地震的分布,以及差不多是任何一个地方的人工水库蓄水后所发生的诱发地震。     

台湾地区地震活动的时间多分形特征研究

利用板块构造、活断层分布、地壳运动这三个方面的最新资料将台湾地区划分为东、西两个地震区和六个地震带。对各地震带11a来的地震目录计算了广义维数Dq和多标度分形谱f(α)，然后绘制成Dq—q曲线和多标度分形谱f(α)—α以及分维时程曲线。综合分析后发现：(1)地震活动的时间结构是多分形而非单一分形结构；(2)台湾地区在大震前后的1～2a内，大震所在的地震带内地震时间结构的Dq—q曲线和多标度分形谱f(α)—α大都出现异常形态；(3)功时程曲线分析可以为强震的时间预报提供有效的客观依据。     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Earthquake Engineering and Engineering Vibration Aims And Scope

正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and     

Solute concentrations in the lower niger river and the source rock contribution

Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO₃ > SO₄ > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1^?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals.     

Scenario predictions for potential near-field and far-field earthquakes affecting Hong Kong

Historical earthquakes noted in the written records of the South China region, including Hong Kong, are not well delineated along identified prominent fault sources. Despite the lack of any definitive, localised trend in the spatial distribution of seismic activity in the region, there does appear to be some major disparity in the seismic activity rates (especially for large magnitude earthquakes) between the near-field and the far-field regions of Hong Kong. Despite this observation, previous studies of the regional seismic activity and seismic ground motion hazard (the latter using a probabilistic seismic hazard assessment, PSHA) have considered very broad source zone regions, in which uniform levels of seismic activity have been assumed. The present paper further scrutinises this broad source zone (BSZ) approach by adopting a novel expanding circular disc (ECD) method to determine the rates of earthquake recurrence. Such a method is intended to counter-check previously developed models by determining earthquake scenario events in terms of magnitude–distance (M–R) pairs or combinations, having defined values of average return period. Unlike the BSZ approach, the ECD method specifically accounts for the supposed variations in the seismic activity rates between events in the near-field and the far-field of Hong Kong.The form of the developed method is particularly suited to the determination of design-level earthquake ground motions for bedrock sites, since it assumes a directionally-independent attenuation model as described in the companion paper. It is found that, whilst the BSZ approach may indicate the overall average levels of hazard that are representative of the South China region as a whole, it does not capture the large disparity in seismic activity rates between near-field and far-field events. This important feature is expected to have a significant impact upon engineering assessments of the seismic safety of structures in Hong Kong and elsewhere in the South China region. For example, it is found that for events with M≥6, the seismic activity rate (normalised by time and area) in the very far-field is around 3.5 times larger than in the near-field and medium-field of Hong Kong. The resulting design M-R combinations, covering a range of return periods from 70 to 2500 years, are limited, for very long return periods and for distant events, by the maximum credible earthquake (MCE) magnitude. Intensive research to determine this seismic hazard parameter is recommended, in order to refine further the results of the ECD analysis, which presently conservatively assumes the MCE to range between M=6 in the near-field of Hong Kong to M=8 in the very far-field, at distances greater than 280 km from Hong Kong.     

Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia

Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer‐scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro‐laminae and calculated sedimentation rate, the micro‐lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo‐Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.     

THEORETICAL APPROACH TO THE SOLUTION OF THE INFILTRATION PROBLEM

ABSTRACT

The one-dimensional transient downward entry of water in unsaturated soils is investigated theoretically. The mathematical equation describing the infiltration process is derived by combining Darcy's dynamic equation of motion with the continuity and thermodynamic state equations adjusted for the unsaturated flow conditions. The resulting equation together with the corresponding initial and boundary conditions constitues a mathematical initial boundary value problem requiring the solution of a nonlinear partial differential equation of the parabolic type. The volumetric water content is taken as the dependent variable and the time and the position along the vertical direction are taken as the independent variables. The governing equation is of such nature that a solution exists for t > 0 and is uniquely determined if two relationships are defined, together with the specified state of the system, at the initial time t = 0 and at the two boundaries. The two required relations are those of pressure versus permeability and pressure versus volumetric water content.

Since the partial differential equation has strong non-linear terms, a discrete solution is obtained by approximating the derivatives with finite-differences at discrete mesh points in the solution domain and integrated for the corresponding initial and boundary conditions. The use of an implicit difference scheme is employed in order to generate a system of simultaneous non-linear equations that has to be solved for each time increment. For n mesh points the two boundary conditions provide two equations and the repetition of the recurrence formula provides n—2 equations, the total being n equations for each time increment. The solution of the system is obtained by matrix inversion and particularly with a back-substitution technique. The FORTRAN statements used for obtaining the solution with an electronic digital computer (IBM 704) are presented together with the input data.

Analysis of the errors involved in the numerical solution is made and the stability and convergence of the solution of the approximate difference equation to that of the differential equation is investigated. The method applied is that of making a Fourier series expansion of a whole line of errors and then following the progress of the general term of the series expansion and also the behavior of each constituent harmonic. The errors (forming a continuous function of points in an abstract Banach space) are represented by vectors with the Fourier coefficients constituting a second Banach space. The amplification factor of the difference equation is shown to be always less than unity which guarantees the stability of the employed implicit recurrence scheme.

Experiments conducted on a vertical column packed uniformly with very fine sand, show a satisfactory agreement between the theoretically and experimentally obtained values. Many experimental results are shown in an attempt to explain the infiltration phenomenon with emphasis on the shape and movement of the wet front, and the effects of the degree of compaction, initial water content and deaired water on the infiltration rate.     

Late Permian post‐ophiolitic trondhjemites from Central Iran: a mark of subduction role in growth of Paleozoic continental crust

Late Permian trondhjemites in the Anarak area occur as stocks and dykes, which cross cut the Anarak ophiolite and its overlying metasedimentary rocks, and are exposed along the northern Anarak east–west main faults. These leucocratic intrusive bodies have enclaves of all ophiolitic units and metamorphic rocks. They are composed of amphibole, plagioclase (oligoclase), quartz, zircon and muscovite. Secondary minerals are chlorite (pycnochlorite), epidote, albite, magnetite and calcite. Whole‐rock major‐ and trace‐element analyses reveal that they are characterized by high SiO ₂ (67.8–71.0 wt%), Al ₂ O ₃ (14.9–17.1 wt%) and Na ₂ O (5.3–8.6 wt%), low K ₂ O (0.1–1.5 wt%; average: 0.8 wt%), low Rb/Sr ratio (0.01–0.40; average: 0.09), low Y (3–6 ppm), negative Ti, Nb and Ta anomalies, slightly negative or positive Eu anomaly, LREE enrichment and fractionated HREE. These rocks present 2 to 40 times enrichment in inclined chondrite‐normalized REE patterns. Geochemical characteristics of the Anarak trondhjemites all reflect melting of a mafic protolith at more than 10 kbar. The field evidence and whole‐rock chemistry reveal that these rocks have been crystallized from magmas derived from melting of subducted Anarak oceanic crust. This study reveals that melting of garnet amphibolite was an important element of continent formation in the study area.