中短期地震前兆的模糊综合识别

本文把模糊模式识别的直接方法用于综合分析多台多种手段观测到的地震前兆资料,以便提取较大地震前几个月内可能出现的中短期前兆异常信息。 所用方法的基本技巧是,对每一个台的每一种前兆观测手段建立起适当的前兆从属函数,并进而确定出多手段或多台的综合前兆从属函数。首先以综合前兆从属函数为基础,识别出某一地区较大地震前出现的中短期前兆异常,然后将其归纳成可用于地震预报的中短期前兆模式。 借助于所提出的方法,本文着重分析处理了1979——1986年间日本东海地区及其邻近地区3个倾斜台、2个验潮站、2个水氡观测站、2个水位观测点和30个体积应变观测点的大量前兆观测资料,识别出了这一期间在该地区内发生的10余次6级以上地震前的中短期前兆异常时间,并得出了两类地震前兆模式:第一类前兆模式适用于在该地区内进行多种前兆手段的综合分析预报;第二类前兆模式适用于单种前兆手段(体积应变)的多台综合分析预报。 为对比起见,文中同时给出了我国唐山7.8级地震及其6.9级强余震前多台水氡含量变化的中短期前兆综合分析识别结果,所得出的前兆模式与日本东海地区的第二类前兆模式相符。      

中短期地震前兆的模糊综合识别

本文把模糊模式识别的直接方法用于综合分析多台多种手段观测到的地震前兆资料,以便提取较大地震前几个月内可能出现的中短期前兆异常信息。 所用方法的基本技巧是,对每一个台的每一种前兆观测手段建立起适当的前兆从属函数,并进而确定出多手段或多台的综合前兆从属函数。首先以综合前兆从属函数为基础,识别出某一地区较大地震前出现的中短期前兆异常,然后将其归纳成可用于地震预报的中短期前兆模式。 借助于所提出的方法,本文着重分析处理了1979—1986年间日本东海地区及其邻近地区3个倾斜台、2个验潮站、2个水氡观测站、2个水位观测点和30个体积应变观测点的大量前兆观测资料,识别出了这一期间在该地区内发生的10余次6级以上地震前的中短期前兆异常时间,并得出了两类地震前兆模式:第一类前兆模式适用于在该地区内进行多种前兆手段的综合分析预报;第二类前兆模式适用于单种前兆手段(体积应变)的多台综合分析预报。 为对比起见,文中同时给出了我国唐山7.8级地震及其6.9级强余震前多台水氡含量变化的中短期前兆综合分析识别结果,所得出的前兆模式与日本东海地区的第二类前兆模式相符。     

地震前兆信息识别的一种人工智能方法

探讨了识别地震前兆信息的新途径。使衙“机器发现”方法，即利用计算机技术，运用递归函数理论处理前兆观测资料，建立其解析函数表达式，并以解析表达式的外推值作为识别异常的标准，实现了对地震前兆信息的定量分析。     

西北地区地震综合前兆信息量S值的应用研究

一个地震前兆观测异常所提供的地震信息一般由异常地点、异常变化量、异常持续时间以及异常完成后的延续有效时间等诸多因素所决定,因此提出了用于描述地震异常的前兆信息量S值。根据地震前兆异常信息量综合数学表达式为基础,充分结合平滑滤波、消周期及趋势项和从属函数等数据处理方法,对西北地区67个观测资料较为连续的前兆主要台项进行地震综合信息量S值的计算与提取。结果表明,S值综合信息量时序曲线在西北地区1986年5月至2005年3月间的10次MS≥5.0地震震前均出现不同程度的高值异常(S≥0.154)。     

多台站地磁观测资料综合处理的一种方法

通过利用空间线性度方法，分析处理地磁场前兆观测资料，并从“场”的角度综合计算多台站的地磁场观测资料，确立地磁基本场的统一信息量－空间线性度ａ。分析处理华北地区多个台站１９７５￣１９９４年的地磁场前兆观测资料。结果表明，中强地震之前约１ａ左右的时间内，空间线性度ａ可能出现明显的下降异常，有些在临震前回升，因此地磁场空间线性度ａ有可能作为中强地震前兆预报的指标。     

用模糊集理论对时变震害作定量估计

本文中,模糊集理论的各种方法,也称模糊数学,已被应用于时变震害的定量估计,获得以下结果: 1.以地震烈度资料为基础对震害作定量估计.应用模糊数学的一些方法,大地震前的地震烈度花样能进行比较清楚地、定量地计算;在某给定区域,大震前高活动周期和地震活动静态周期能被识别;地震活动的暂时变化和地震间隙的相似性也能被检测出来.另一方面,根据一系列的地震烈度统计指标,也可以直接估计时变震害.文中模糊集分析的两种方法.即模糊类比法和模糊花样识别直观法都很有特色.模糊集分析方法之一是基于模糊网;其二是根据模糊等效关系.2.以不同前兆观测资料为签础对震害作定量估计,模糊花样直观法适于研究不同种类地震前兆.根据被识别前兆的时间和空间特征,将能估计不同时期震害.本文主要研究中国和日本观测到的中、短期前兆.     

福建地区地下流体异常与中强地震福建地区地下流体异常与中强地震

在对福建的地下流体资料进行综合分析的基础上，提取了1990年以来闽台地区若干次中强地震的前兆异常信息，并对异常点的变化形态、时间、空间分布与地震活动特征进行了研究，初步掌握了闽台地区地震前地下流体中、短期或临震的前兆异常特征，并发现在不同的观测位置，将出现不同的地下流体前兆异常。     

线性度方法在前兆观测数据分析处理中的应用

利用空间线性度方法，对前兆场中不同台站，不同学科的前兆观测数据从总体形态上进行综合分析，得到关于描述前兆场的新的特征量ａ（空间线性度）本文给出了空间线性度的具体计算方法，并以华北地区为例，分析处理了区内１９７０～１９９４年部分地电阻率和地下水位观测资料，所得结果表明，新的前兆特征量ａ在中强地震之前一年左右时间内有异常显示。     

地震前兆观测时间序列的无量纲化

地震前兆观测时间序列的无量纲化，对多台项或多前兆观测时间序列综合信息提取是十分重要的，有利于区域性地震前兆监测系统各种短期或短临观测异常信息的统一表达和定量综合信息提取，直接为综合地震预报服务。本文给出了多种前兆观测时间无量纲化的一般表达，归纳了电磁，用于综合分析的几种探索性方法，供参阅。     

固体潮潮汐因子特征频谱及其应用

本文应用非线性谱分析中的最大熵谱分析方法（ＭＥＭ）、和一般线性功率谱的分析方法，对固体潮潮汐因子的时间序列进行了综合研究，指出固体潮潮汐因子的时间序列中普遍存在明显的半月左右周期的特征频谱。将其应用于地震前兆的分析的分析与探索，对固体潮潮汐因子特征频谱中前兆变化特征进行了解释，得出结论：半月左右的频率域，是固体潮观测中前兆响应的一个和重要主频域。     

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.