1999年9月14日四川省绵竹清平5.0级地震前区域地震活动

1　空间分布我们采用四川省地震台网目录资料 ,选取发生在北纬 3 0°3 0′～ 3 0°5 0′,东经 1 0 3°5 0′～1 0 5°1 0′德阳及邻区内的地震 ,对 1 970年以来的资料进行了分析。据统计 ,1 970年至 1 999年1 0月 ,该区发生 3 .0级以上地震共 85次 (图1 )。 1 999年 9月 1 4日绵竹清平 5 .0级地震为图 1　德阳地区 M≥ 3.0地震分布图近 3 0年来的最大地震 ,其次是 1 970年 3月 2 2日什邡、绵竹九顶山间 4.9级地震。历史上最大的地震为 1 95 8年 2月 8日绵竹 (微观震中 )6.2级地震 ,宏观震中为北川 ,震害较为严重。2　频次异常从 M-t、 N -…     

兴海6．6级地震前海东地区前兆资料异常特征

20 0 0年 9月 1 2日在青海省海南州兴海县以北 ( 3 5°1 5′N ,99°3 0′E)发生了Ms6 6级地震 ,随后又发生多次余震 ,其中 5级以上强余震 5次。兴海地震前青海省海东地区所属台站的一些前兆观测项目均出现了不同程度的异常 ,分析与研究这些异常特征对于及早发现地震异常信息、预报地震以及减轻地震灾害有着重要的意义     

新疆21号温泉震前短临前兆异常的分析

0 前言 1990年6月14日北京时间20时47分19.7秒,原苏联斋桑地区(东经85°03′,北纬48°06′),发生7.3级强烈地震;8月3日17时15分,该地区(东经84°43′,北纬48°29′)又发生6.8级强烈地震;随后10月25日7时38分16.7秒在乌苏发生5.2级、7时46分59.6秒又发生5.0级地震;11月12日,原苏联伊塞克湖又发生6.7级地震。1991年6月6日16时16分,和静县北部阿拉沟附近发生5.2级地震;9月18日乌鲁木齐东南发生4.5级地震。这几次地震前,21号井温泉动水位和温泉温度均出现不同程度的短临异常。     

使用视电阻率预测安县-绵竹间5.0级地震的实践

1999年 11月 30日在四川省安县、绵竹间 (10 4°2 4′E ,31°2 4′N)发生了Ms5 0地震。笔者根据成都台地电NE道视电阻率观测资料 ,在震前发现了异常现象 ,经过落实后确认了异常 ,并结合地震活动形势作出了其后一段时间在绵竹附近地区可能发生 5级以上地震的判断。事实证明成都台地电资料具有一定的前兆反映能力。     

全球地震纬度分布特征和北纬35°峰值异常浅析

本文取1900年─1980年全球Ms≥6．0地震7936次分析后发现，地震发生在南北回归线（23°5N—23°5S）之间占49．69％，发生在南北极因（63°5N—63°5S）之间占99．17％，发生在南北极圈外只占0．83％，即很少发生地震；其中8级地震98次，在35°N线为高峰。又分析了公元648年─1979年全球M≥8级地震257次主要亦集中在35°N线附近。尤其是历史上破坏性极大的地震在35°N线附近者多。这些现象可能和地球自转有一定关系。     

2001年云南地区地震活动概述

1　地震活动概况据昆明区域数字地震台网测定 ,2 0 0 1年 1月至 1 2月云南地区 (2 1°～ 2 9°Ｎ ,97°～ 1 0 6°Ｅ)共发生Ｍ≥ 3 0级地震 1 88次 (不含余震 ) ,其中 3 0～ 3 9级地震 1 49次 ,4 0～ 4 9级地震 2 7次 ,5 0～ 5 9级地　　图 1　 2 0 0 1年云南地区Ｍ≥ 3 0级地震Ｍ -ｔ图震 1 1次 ,6 0级地震 1次。 2 0 0 1年云南省内共发生Ｍ≥ 5 0级地震 7组 9次 ,分别是 3月 1 0澜沧 5 0级地震 ,4月 1 0、1 2日和 6月 8日施甸 5 2、 5 9和 5 3级地震 ,5月 2 4日宁蒗 5 8级地震 ,7月 1 0日楚雄 5 3级地震 ,7月 1 5日江川5 0…     

1999年震情述评

1　全球地震活动概况据我国地震台网测定 ,1 999年全球发生 7级以上地震 2 1次 (表 1 ) ,最大地震为 8月 1 7日土耳其 7.8级地震 ,其次为 9月 1 6日台湾南投 7.6级和 1 0月 1日墨西哥南部沿海 7.6级地震 (图 1 )。　　表 11999年全球 7级以上地震目录序号月日时 分 秒纬度经度地点　　　　　震级0 10 2 0 70 5 47 49.7 12 .1°Ｓ 16 7.0°Ｅ新赫布里底群岛北 7.20 2 0 30 82 0 2 5 48.45 2 .2°Ｎ 15 8.2°Ｅ堪察加 7.30 30 32 0 18 47 48.2 5 1.4°Ｎ 177.9°Ｗ阿留申 7.00 40 40 5 19 0 8 0 3.80 4.8°Ｓ 15 0 .7°Ｅ巴布亚几内亚 7.…     

2001年7月11日甘肃镜铁山5.4级地震震源机制解刘旭宙

20 0 1年 7月 11日 0 5时 4 1分 3.8秒 ,甘肃省镜铁山发生了ＭＳ5 .4地震 .经甘肃省地震监测台网测定 ,该次地震震中位于 39.2°Ｎ ,98.0°Ｅ ,震源深度 10ｋｍ .作者收集了甘肃及青海地区共 2 6个地震台站的Ｐ波初动资料 ,求出了该次地震的震源机制解 ,见表 1和图1.表 1　 2 0 0 1年镜铁山ＭＳ5 .4地震震源机制解节面参数 Ａ节面Ｂ节面 应力轴参数 Ｐ轴Ｂ轴Ｔ轴倾向 2 2 0° 13 0°方位角 2 65° 2 10° 175°倾角 86° 82°仰角 90° 0° 90°　　 矛盾比 :0 .0 36图 1　 2 0 0 1年 7月 11日甘肃镜铁山　　　 5 .4级地震震源机制解Ｆｉｇ…     

2002年震情述评

1　全球地震活动概况据我国台网测定 ,2 0 0 2年全球共发生 7级以上地震 1 6次 (表 1 ) ,最大地震为 1 1月 2日印尼苏门答腊 7 8级和 1 1月 4日美国阿拉斯加的 7 8级地震 (图 1 )。 2 0 0 2年全球地震活动仍维持前几年的活动格局 ,与 2 0 0 1年相比地震频次及所释放的能量都明显下降。 2 0 0 2年全球 7级以上地震活动有以下特点 :　　表 1　 2 0 0 2年全球 7级以上地震目录序号月日时 -分 -秒纬　度经　度地　　点震　级0 10 10 30 1 2 2 5 1 0 17 6°Ｓ 16 8 0°Ｅ新赫布里底群岛 7 6　　　　　0 2 0 30 32 0 0 8 0 1 136 4°Ｎ 6 9 8°…     

鲁皖豫交界地区地震活动特点及趋势分析

引言本文所述的鲁皖豫交界地区是指 3 1 .5°～ 3 6°N,1 1 3 .5°～ 1 1 7°E的范围。据历史地震记载 ,1 40 0年以来该区共发生 M≥ 6的地震 1 0次 ,最大地震为 1 93 7年荷泽 7.0级。近期地震活动实况表明 ,1 983年荷泽 5.9级地震后 ,研究区中等地震活动出现约 8年的平静 ( 1 984～ 1 991 )后 ,于 1 992年开始活动 ,特别是近两年来 ,连续发生 5次中等地震( 1 998年 1月 2 6日濮阳 4 .0 ;1 999年 5月 2 0日濮阳 4 .0 ,1 2月 3 0日阜阳 4 .6;2 0 0 0年 1月 2 8日随州 4 .1级及 4月 2 6日成安 4 .1级地震 )。这种由平静转为活跃的特点是否预…     

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.