青海热水-日月山断裂带古地震的初步研究

热水—日月山断裂带是青藏高原东北缘柴达木—祁连山活动地块内部一条重要的NNW向的右旋走滑活动断裂带.断裂活动形成了一系列山脊、冲沟和阶地等右旋断错微地貌及断层崖、断层陡坎等垂直断错微地貌.本文对发生在该断裂带上的古地震事件开展了研究,综合探槽剖面和断层陡坎年代,大致可以确定两次古地震事件,其年代分别为距今6280±120a,2220±360a,复发间隔约4000a左右.     

兰州马衔山北缘断裂带古地震初步研究

兰州马衔山北缘断裂带为一条全新世活动断裂 ,大致由 4条次级断裂段组成 .沿断裂带发现了多期古地震事件 ,其活动具有时空不均匀性 .其中东段的马衔山段可以确定 2次古地震事件 ,距今 5850± 50 0aB .P .,2 0 60± 42 0aB .P .,复发间隔约 380 0a ;震级 7～ 7.5级左右 .中段的七道梁段发现 2次古地震事件 ,距今 1 682 0± 80aB .P .,1 0 80 0± 1 40aB .P ..西段的雾宿山咸水沟段可以确定一次古地震事件 ,其年代为 1 2 45± 560aB .P .,结合史料考证结果 ,认为就是 1 1 2 5年兰州 7级地震 .从古地震活动年代及复发间隔分析 ,马衔山北缘断裂带未来的强震危险段应为东段的马衔山段和西段的雾宿山咸水沟段 .     

东昆仑断裂带东段玛曲断裂古地震初步研究

东昆仑活动断裂是青藏高原东北部一条重要的NWW向边界断裂。玛曲断裂位于东昆仑断裂带的最东段。本文通过3个古地震剖面揭示出东昆仑断裂东段玛曲断裂全新世共有4次古地震事件。最新一次古地震事件为距今(1730±50)～(1802±52)a,第二次古地震的时间为距今(3736±57)～(4641±60)a;第三次为距今(8590±70)a;第四次为距今(12200±1700)a。其中第一次和第二次古地震事件的时间较为可靠,两次古地震事件之间的复发间隔为2400a左右,由此认为东昆仑断裂带东段的古震事件之间的复发间隔为2400a左右,古地震的离逝时间为距今(1730±50)～(1802±52)a。     

祁连山北缘佛洞庙-红崖子断裂古地震特征初步研究

佛洞庙-红崖子断裂位于祁连山北缘断裂带中部,是祁连山与河西走廊之间的一条重要边界断裂,断裂全长约110km,总体走向北西西,该断裂为一条全新世活动的逆-左旋走滑断裂,断裂活动形成了一系列陡坎、断层崖以及冲沟和阶地左旋等断错地貌.本文通过3个探槽剖面对发生在该断裂上的古地震事件进行了分析,可确定地震事件2次,事件Ⅰ为历史地震,发生在距今400年前,为1609年红崖堡71/4级地震;事件Ⅱ的年代为距今（6.3±0.6）ka B.P.和（7.4±0.4）ka B.P.之间.同时结合前人的一些研究资料,对古地震的复发模式和间隔进行了初步讨论.     

川西理塘断裂带平均滑动速率、地震破裂分段与复发特征

理塘断裂带是川西北次级块体内部的一条活动断裂带.野外调查获得其晚第四纪断错、近代地震破裂、破裂分段的新证据, 估算出断裂的滑动速率、特征地震震级与复发间隔.结果表明, 理塘断裂带由毛垭坝盆地北缘、理塘和康嘎-德巫等三条次级断裂组成, 以左旋走滑为主, 不同部位伴有不等的逆倾滑分量. 由7个地点的断错地貌及相关沉积物年龄估算断裂带距今约14 ka以来的平均左旋滑动速率为4.0±1.0 mm/a, 垂直(逆)滑动速率0.1~1.8 mm/a; 三条次级断裂均为独立的地震破裂段, 相应特征地震最大矩震级估值为7.0~7.3, 平均复发间隔为500~1000年, 北西段最晚地震破裂发生在距今119±2 a之前, 中段发生在公元1890年前后, 南东段则发生在公元1948年, 显示出与段落之间应力触发作用有关的地震破裂事件沿断裂带单向迁移的特点.     

云南龙蟠—乔后断裂剑川段古地震初步研究

通过遥感影像解译和详细的野外考察,发现龙蟠乔后断裂带剑川段晚第四纪以来长期活动,横跨断裂的水系左旋断错量可分为40 m、140m、550 m、1040m四个等级。经详细考察.后选择后菁拉分盆地开挖探槽。探槽揭示了两次M>6.5古地震事件:一次发生在10010±40aB.P.之前;另一次发生在6130±40a B. P.和6320±40a B.P. 之间。结合前人研究,分析得出剑川盆地全新世以来发生了3次M>6.5的地震,发生时间分别为1751 年、6230士130a B. P.和10737±468aB.P.,其重复间隔约为5300a。由于1751年剑川6¾级地震相对于前两次地震释放的能量偏小,而且其离逝时间较前一次要明显长一些,故本段的地震危险性仍值得关注。     

内蒙古色尔腾山山前断裂带乌加河段古地震活动

通过对色尔腾山山前断裂带乌加河段断层地貌研究，并结合前人对断裂带断裂活动性的工作，分析得到乌加河活动断裂段晚更新世晚期(距今1.445～2.234万年)以来平均垂直位移速率是0.48～0.75 mm/a，全新世早中期以来(距今5 570～8 830年)平均垂直位移速率是0.56～ 0.88 mm/a．利用5个探槽中揭露的古地震现象，结合前人对该断裂带古地震的研究结果，分析确定出2.7万年以来，色尔腾山山前断裂乌加河段共揭露出5次古地震事件，重复间隔约为4 300～4 400年．距今8 000～9 000年之间可能为一个古地震丛，而距今1～2万年之间可能遗漏了两次古地震事件．对比断层陡坎的高度与探槽中揭示出古地震事件的位移和，以及由断层平均位移速率和一次事件的位移得到古地震的重复间隔，得到阿拉盖兔探槽中缺失了3次古地震事件，整个活动断裂段上可能缺失了两次古地震事件．      

安宁河断裂带北段的古地震事件及其在地震研究中的意义

安宁河断裂带是四川省西部的重要强震带。史料表明,安宁河断裂带上的强震主要集中在安宁河断裂带冕宁—西昌一段。冕宁以北没有强烈破坏性地震的记载。本文在安宁河断裂带冕宁以北地段断错地貌特征研究的基础上,根据拖乌以西野鸡洞的探槽揭露讨论了该段的古地震事件。认为该段具有发生7级地震的能力。根据探槽中~(14)C年代测定,古地震的平均重复间隔为940±150年。由于最近一次古地震的发生距今时间已接近其平均重复间隔,因而笔者认为该段已具备再次发生7级地震的能力而应予充分注意。     

内蒙古色尔腾山山前断裂(乌句蒙口-东风村段)的断层活动与古地震事件

通过对色尔腾山山前断裂乌句蒙口 -东风村段的遥感资料解释、野外地质地貌考察 ,并通过对重点地段的古地震探槽开挖 ,获得了该断裂段晚更新世晚期以来的垂直位移速率是 0 88～ 1 83mm a ,全新世中期以来的垂直位移速率是 0 89mm a。通过 2个大型探槽的开挖、古地震事件分析和相关堆积物的断代研究 ,以及用逐次限定方法分析整个断层段上的古地震事件 ,认定该断裂段上全新世以来发生了 5次古地震事件 :事件 1发生在距今 90 0 0± 130 0年 ,事件2发生在距今 6 5 0 0± 5 0 0年 ,事件 3发生在距今 5 5 70年左右 ,事件 4发生在距今 4 2 0 0± 30 0年 ,事件 5发生在距今 32 5 0± 2 5 0年。晚更新世晚期到距今 1万年之间 ,古地震事件很不完整。全新世以来的 5次古地震事件表现出一定的丛集特征。最早的一丛事件发生在距今 890 0年左右 ,第2丛发生在距今 6 5 0 0～ 5 70 0年之间 ,第 3丛事件发生在距今 32 5 0～ 4 2 0 0年之间。第 1丛与第 2丛古地震事件之间间隔为 2 4 0 0年左右 ,而第 2丛与第 3丛古地震事件之间仅间隔 15 70年左右。距今 32 5 0年以来 ,该断裂段上还没有发生过错断地表的地震事件 ,已经超出了古地震丛之间的重复间隔。因此 ,它是色尔腾山前活动断裂带上具备潜在危险的一个活动断裂段。     

鲜水河断裂带乾宁-康定段的滑动速率与强震复发间隔

鲜水河断裂带乾宁——康定段的几何结构比较复杂，由雅拉河、色拉哈——康定、折多塘和磨西4条次级断裂组成，历史上曾发生过1725，1786和1955年3次7级以上强震．本文在断错地貌和年代学（14C 和TL）研究结果的基础上，确定的鲜水河断裂带乾宁——康定段各分支断裂晚第四纪以来的平均水平滑动速率分别为:雅拉河断裂:（2.00.2）mm/a；色拉哈——康定断裂:（5.50.6）mm/a；折多塘断裂:（3.60.3）mm/a；磨西断裂:（9.90.6）mm/a． 历史地震地表破裂、同震位错和古地震资料研究结果表明，雅拉河断裂具有上千年的强震复发间隔，色拉哈——康定和折多塘断裂强震复发的平均间隔在230～350ａ，未来百年均不存在强震复发的可能性；磨西断裂强震复发间隔在300ａ左右，上一次的1786年7级地震距今已达213ａ，未来百年正处于新一轮的强震复发背景之中．      

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.