现代地震记录

由于我国数字地震学研究起步较晚，在很多地震学家中，对于数字地震学的意义和数字地震资料的使用还存在不少疑问。本文结合中国数字地震台网（ＣＤＳＮ）的工作，对经常提出的比较集中的两个问题，即数字地震记录的物理意义和数字地震记录与传统地震记录有哪些不同的问题进行了回答和讨论。     

发展中的山东数字地震台网

山东数字地震台网承担山东地区及附近海域的大震速报和微震监测任务。随着国民经济的发展和数字化技术的成熟,在“八五”期间建设了济南无线遥测地震台网;“九五”期间改造建成了数字遥测地震台网;“十五”期间山东数字地震台网建设后,台站布局、监测能力、大震速报效能得到加强,为地震研究、地震速报、地震应急提供了可靠的技术平台。     

安徽"十五"数字地震观测技术系统

前言在中国地震局与安徽省政府的大力支持下 ,“九五”期间安徽省地震局完成了合肥数字遥测地震台网、蒙城区域有人值守数字地震台、国家数字地震台网合肥台的建设 ,现投入正式观测运行 ,并取代了原模拟观测。但是监测设施的数字化改造仅占全省地震台网的2 7% ,合肥数字地震台监控 ML 2 .5地震范围仅为全省地域面积的 1 / 3 ,而皖南、皖北地区台站仍为模拟观测 ,难以适应新形势下安徽省防震减灾事业发展需求 ,因此 ,在“十五”期间将建设省级数字地震台网。图 1是“九五”期间安徽省数字地震台网的建设概况。1　“十五”安徽省级数字地震观…     

浅谈数字地震台网观测资料质量的提高

引言数字记录地震仪具有记录频带宽、分辨率高、动态范围大,以及易于与计算机联接的优点,1975年全球开始在地震观测系统中采用数字记录方式,使地震学的发展出现了一个飞跃。我国于1987年开始中美地震科技合作项目,建立了中国数字地震台网(CDSN),通过“八五”、“九五”期间的中国数字地震观测系统建设,尤其是正在建设中的“十五”项目,经过中国地震局和有关部门的重视和支持,以及广大地震科学工作者和工程技术人员的努力,现已建立了比较完善的数字地震观测网络系统。模拟地震观测在为人类做出约100年的贡献后,作为地震观测的一种科学手段…     

日本的太平洋超高性能数字化地震观测台网计划

1.全球地震学的国际合作为了能记录和分析在广大的分散地区的地震资料,建立全球地震台网是十分必要的。为了推进地震和地球内部的研究,许多国家设计并建立了新的地震观测台网。法国最近设计并建立了法国全球地震台网(GEOSCOPE)。西欧国家目前正在制定“ORF-EUS”地震台网计划。中国现已建立了新的地     

加强区域数字地震台网建设推进数字地震学的应用研究

简要回顾了数字地震学诞生以来所取得的科学成果。结合我国地震观测系统大规模数字化改造的实践,着重阐述了区域数字化地震台网的观测优势,以及在台网建设目标、观测资料的充分利用和高素质人才培养方面存在的劣势和不足。还提出了对关于区域数字地震台网建设和发展过程中的指导思想、“软件”和“硬件”的关系、基础和应用研究与地震预报的关系、数字地震学的发展与高素质人才培养的关系等等问题的思考和建议。     

中国地震台网数字化改造的进展

介绍了九五期间（1996~2000年）中国地震台网数字化改造的进展和首都圈数字地震台网（1999~2001年）的建设情况，重点介绍了国家数字地震台网、区域数字地震台网和流动数字地震台网的台站分布、仪器配备和主要任务．      

中国数字地震台网所使用的仪器及其传递函数的计算方法

2000年以来我国地震观测系统得到了迅速的发展,目前,已建成了由国家数字地震台网,区域数字地震台网,火山数字地震台网和流动数字地震台网组成的新一代中国数字地震台网。本文介绍了中国数字地震台网的仪器配置情况和各种仪器的主要参数,并结合我国数字地震台网中使用的地震观测系统,阐述了仪器传递函数的计算方法。     

中国国家地震台网中心技术系统

“中国数字地震观测网络”项目完成后,我国的地震监测能力得到了很大提高．相比“九五”期间,“十五”计划完成后中国国家地震台网中心的技术系统得到了全面提升．新技术系统庞大而复杂,刚刚运行就成功经受了汶川MS8.0特大地震的考验．本文详细介绍了中国国家地震台网中心技术系统的整体情况及其所包含的子系统的情况．例如,全国测震实时数据流系统、国家台网实时处理系统和人机交互分析系统等．      

中国数字地震台网(CDSN)的现状和进展

1　中国数字地震台网概况中国大陆邻接印度、欧亚和太平洋板块的边缘 ,其特点在于具有复杂的地壳构造和高地震活动性。中美合建的中国数字地震台网 ( CDSN)运行 1 5年来 ,在中国地震学研究中发挥了重要的作用。CDSN作为美国地震学联合研究协会 ( IRIS)部署的全球地震台网 ( GSN)的参与伙伴 ,为全球地震学研究做出了贡献。CDSN系中美地震研究科技合作议定书中的项目 ,也是两国政府间的科技合作项目之一。台网的建设始于 1 983年 5月 ,历经 3年的场地准备和技术实施 ,于 1 986年 7月建成。1 986年 1 0月 1日起 ,CDSN数据管理中心以…     

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.