应变固体潮相位与地震的关系

文中选取华北地区46次ML≥5.0地震为参考依据,计算出了其发生时刻的固体潮相位。表明,华北地区的中强地震多数发生在固体潮相位的π/2或3π/2时刻。显示出在固体潮波上存在着两个特殊相位发震概率较大。这种在应变固体潮最大或最小时段发震的现象说明,固体潮波变化形态不一定是造成地震的根本原因,但地震的发生明显受到日月引力等外部条件的影响,尤其是华北北部燕山褶断带的地震最为突出。     

倾斜固体潮对我国若干地震的触发作用浅析

本文研究了我国历史与现今中强以上地震的发震时刻与倾斜固体潮的关系。结果表明,地震发震时刻位于震中区当天倾斜固体潮的峰值时段上。孤立型地震的发震时刻往往与震中区倾斜固体潮极大值对应;原地重复发生的地震,其发震时刻所处的倾斜固体潮背景相同;逼近地震与主震发震时刻的倾斜固体潮背景相同的占70%;大震后有60%的强余震与主震发震时刻的倾斜固体潮背景相同。据此,成功地预报了门源6.4级地震后的较大余震。     

发震时间与潮汐引力

地震预报，即震级、震中位置和发震时间的预报等，仍是当今世界公认的难题。笔者通过对公元1303年～2003年间全球3386次震例的统计，发现有60％以上的中强地震发生在井水位固体潮的增压时段，进而对发震时间与井水位固体潮的关系进行了分析探讨。     

唐山老震区M_L≥2.0地震发震时刻与固体潮极值时刻之时差分布特征

以固体潮极值时刻与地震发震时刻的时间差为参数,统计了唐山老震区M_L≥2.0地震的时差在月、半月、日、半日尺度下的各时间分段内的频度分布。结果显示唐山地区的地震活动高频度时段与固体潮极值时刻有对应性,表明其在一定程度上受到了固体潮作用的影响。其中唐山断裂中东段的地震落入触发时段内的几率更大,似乎意味着唐山地区的应力集中区主要还是集中在唐山断裂中东段。另外,强震之后1~3周余震受固体潮极值的影响显著,所以此时间内应更加注意在固体潮接近极值时发生强余震的可能性。     

新疆地区6级以上地震前小震固体潮调制比异常演化特征

选取新疆地区2016年以来发生的3次M_S 6.0以上浅源地震,对发震前震中区小震调制比变化进行系统对比分析,发现3次地震前均出现不同程度的固体潮调制比异常：①2016年12月8日呼图壁M_S 6.2地震仅在震前2年于震中出现调制比高值异常;②2017年8月9日精河M_S 6.6地震震中于发生前2年、1年、0.5年均落于调制比高值异常区域,受调制作用较明显;③2020年1月19日伽师M_S 6.4地震于发生前2年、1年,在震中位置附近出现调制比异常。     

北京太平庄井水位固体潮畸变与地震的关系

太平庄井在地震前能灵敏地记录到水位固体潮畸变异常。据１９９４年元月～１９９６年４月间发生的震例，发现水位固体潮畸变波动是由复杂的多周期、次高频波动构成的，在震前１０天或半个月内出现。为避免多震异常重叠的干扰，提取并分析了单震畸变震例，认为：（１）该井能记录到世界强震前的水位固体潮畸变信息；（２）在一定范围内畸变异常时段与震级成正变关系；（３）研究水位固体潮畸变异常，将会为地震预报开辟一条新途     

山西地震带历史地震序列的统计分析

在工程地震工作中需要知道某地震带或某地区未来100年内的地震活动水平,以便适当选择历史地震的统计时段,从而得到和地震活动水平相适应的不同潜在震源区的各级地震的年平均发生率。 本文利用极值理论、最大熵原理、马尔可夫模型的方法、莫尔纳方法和伯努里模型方法计算了山西地震带未来100年内中强震的年平均发生率、平均重现期大于等于某级地震的个数和发震概率,计算结果表明,山西地震带未来百年内将发生≥6.0级地震3次,发震概率为0.94左右;将发生≥6.5级地震1—2次,发震概率为0.84左右;有可能发生≥7.0级地震,发震概率为0.53左右;发生≥7.5级地震的可能性不大,发震概率为0.32左右;发生≥8.0级地震的可能性很小,发震概率为0.15左右。     

国内外震情

20 0 0年 1 0月华北地区 ML≥ 3.0地震动态根据中国地震局分析预报中心提供的资料 ,2 0 0 0年 10月华北地区 (33.0°～ 42 .0°N,111.0°～12 5 .0°E)共发生 ML≥ 3.0地震 4次 (见表 1) ,无 ML≥ 4.0地震发生。 10月 13日 15时 48分黄海ML 3 .4地震和 10月 2 6日 11时 2 6分新绛 ML≥ 3.4地震是本月最显著的事件。本月地震频度与9月持平 ,震中主要分布在华北西部和东部。其他地区相对较为平静。表 1　 2 0 0 0年 10月华北地区 ML≥ 3.0地震序号发　震　时　刻　　年月日时分秒　震中位置φN/°　　 λE/°震级 /ML 震　中0 12 0 0 …     

门源6.4级地震后较大余震的试报与固体潮触发地震的初步研究

本文分析了固体潮对地震的触发作用,认为我国大多数中强以上地震与固体潮有相关性。通过对任意选择的几十例地震分析,发现这些地震的发震时刻往往处于倾斜固体潮理论值的峰值段上,其中单发性地震、原地重复性地震、逼近地震与主震以及大震后强余震在发震时间上与各自的倾斜固体潮背景都有密切关系,有一定的规律性及统计意义。用本方法对1986年8月26日门源6.4级地震后较大余震进行试报,效果很好。由于固体潮汐是地球上最大的周期性应变,所以成为触发地震的一个极可能因素。     

论地震的“发震时段”

用地震电磁波法作临震预报，发现地震的发震时间是有规律性的，仪器到的辽南发生的地方震和有些大地震，就是在预测的“发震时段”里发生的。     

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.