利用辽宁区域地震台网记录分析重复地震

将Schaff和Richards所选的通过远震波形相关得到的分布在辽宁地区的23对ldquo;重复地震rdquo;,利用辽宁区域地震台网记录的波形资料进行相关计算,得到辽宁区域台网波形相关意义上的ldquo;重复地震rdquo;,并与Schaff和Richards的结果进行了对比分析. 利用辽宁区域台网得到的ldquo;重复地震rdquo;对辽宁区域地震台网的震相拾取和地震定位进行了评估. 结果表明,远震波形相关意义上的ldquo;重复地震rdquo;与区域台网波形相关意义上的ldquo;重复地震rdquo;有一定差别,它们只有部分交集. 但是,从总体上评估辽宁区域台网的定位能力和震相拾取误差,用两种方法得到的ldquo;重复地震rdquo;所给出的评估结果无实质差别——尽管用区域台网得到的ldquo;重复地震rdquo;似乎效果更好. 基于ldquo;重复地震rdquo;之间在理论上距离应小于1 km的工作假定,可以得到辽宁区域台网地震目录中的定位误差在5 km之内,平均为2 km;Pg震相的拾取误差94%在plusmn;1 s之间,Sg震相的拾取误差88%在plusmn;1 s之间.      

甘肃测震台网监测能力及地震目录完整性分析

区域地震台网监测能力的科学评估,是进行区域地震活动性和地震危险性分析的重要基础,最小完整性震级Mc是表征台网监测能力的关键．本文以甘肃测震台网的地震观测报告和区域地震目录为基础资料,分析了甘肃及邻区地震监测能力在时、空上的分布特征,利用ldquo;震级 序号rdquo;法、ldquo;最大曲率rdquo;法(MAXC)、拟合度分别为90%和95%的拟合优度检验法(GFT)及ldquo;完整性震级范围rdquo;法（EMR）等,研究了甘肃区域地震目录最小完整性震级Mc的时、空分布特征．结果表明,1980年以来甘肃测震台网的地震监测能力得到了逐步提高,模拟记录时期和ldquo;九五rdquo;期间甘东南地区的地震监测能力明显高于祁连山地震带中西段,ldquo;十五rdquo;测震台网运行后,甘肃及邻区的地震监测能力的空间差异明显缩小．最小完整性震级Mc和监测能力的时空分布特征具有较好的一致性．随着台网的改造,Mc逐步降低,ldquo;十五rdquo;台网运行后,甘肃及邻区的ML1.8以上地震基本完整．此外,还讨论了相关技术规范对区域台网地震目录的影响,并且提出了消除该影响的科学途径和有效方法．该研究结果可为甘肃及邻区地震活动性分析和地震危险性评价等相关研究提供参考．      

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．      

中国地震台网的建设与发展

正从1996年开始,中国地震局进行了大规模数字地震观测系统建设,通过"中国数字地震监测系统""中国数字地震观测网络"和"中国地震背景场探测"3个重点项目的实施,已建成由国家地震台网、区域地震台网和流动地震台网组成的数字地震观测系统。(1)国家地震台网。国家地震台网是一个覆盖中国的地震监测台     

中国地震台网观测系统特性分析与资料应用研究

正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。中国地震台网中心每天汇集的数据量达到40GB,可以说,我国地震台网产出的观测数据积累到了一定程度,如此海量的地震波形数据为地震监测与研究提供了丰富的原始资料,     

九江-瑞昌MemＳsub5.7地震地磁异常的观测与分析y

2005年11月26日九江——瑞昌MＳ5.7地震发生前,震中及其周围地区的地磁基本场测量和相应的ldquo;2005.0中国地磁基本场曲面样条模型rdquo;显示,震中周围100 km范围内存在显著的ldquo;2005.0九江——瑞昌地磁基本场水平分量异常rdquo;. 而该异常在ldquo;1970.0中国地磁基本场曲面样条模型rdquo;中并不存在. 2005年12月在震中及其周围地区的21个测点上进行了地磁重复测量, 并建立了ldquo;局部修订2005.0中国地磁基本场曲面样条模型rdquo;. 该模型显示,震后ldquo;2005.0九江——瑞昌地磁基本场水平分量异常rdquo;明显减弱. 因此认为,ldquo;2005.0九江——瑞昌地磁基本场水平分量异常rdquo;是地震地磁前兆异常现象.      

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。     

大连台使用CTS-1记录波形特点

自"九五"数字化改造以来,作为国家数字台网重要组成部分的大连地震台配备了数字地震观测系统(CTS-1),使台站的地震观测水平和观测质量有了质的飞越。大连地震台通过长时间对不同类型及不同震中距的地震震例分析、讨论与研究,总结出了大连地震台的地震波形及震相特征。大连台使用CTS-1记录波形特点。     

中国数字化地震观测系统

介绍了中国地震局“九五”重点项目中国数字化地震观测系统，特别重点介绍了中国数字化地震台网、国家标准数字化地震台、中国地震局卫星数据通信网、中国数字地震台网中心的建设规模、设计思路、技术参数、设备结构、服务功能，以及中国数字地震台网的运行流程和运行状况。     

20年数字地震观测技术发展

<正>"八五"期间,中国提出发展自己的数字地震观测系统,比西方落后近20年,形成的数字地震观测系统分为台网、流动台网和台站3部分。区域台网和流动台网的试验系统分别在北京遥测地震台网和江苏省地震局进行试验,发现并提出了一系列问题。"九五"期间,对改进后的自主研发数字地震现测系统在部分区域台网推幵,改进、推广经历了一段艰辛的历程:经过设备与软件改进,     

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.