霍山"震情窗"地区流动地磁S异常与华东中强地震相关性的研究

以霍山“震情窗”地区流动地磁测线的S值变化,预测霍山“震情窗”相关地区－华东地区中强地震,研究结果表明：“震情窗”地区流动地磁测线的S值异常与距离霍山“震情窗”R＜500km的华东中强地震有明显的相关性。     

中小地震的流磁异常信息

在孕震区形成期间，流动地磁测线各测点的局部地磁场因受孕震区应力场的主控，可能出现δf“同向”变化的现象，从而整条测线同一期各测点或同是δf＞0，或同是δf＜0。笔者认为整条流动地磁测线同一期各测点出现分“同向”变化，可能是流动地磁测线邻近地区中小地震的流动地磁异常信息。     

六安流动地磁测量异常的映震能力探讨

将安徽省六安地区流动地磁测线12个流动地磁测点的∑│δfi│异常与安徽中西部地震活动性作对比分析，初步结果为：12个流动地磁测点的∑│δfi│≥Fu），一年内安徽中西部地区的地震活动性增强；反之，则安徽中西部地区的地震活动性较弱。此方法在地震的中短期预报中有一定的实用意义。     

福建沿海地区流动地磁测量对大于ML4．0级震的映震能力分析

利用1990年以来福建沿海地区流动地磁观测资料,以｜δfij｜≥3nT为异常指标,对同一期｜δfij｜≥3nT的测点数作统计,分析研究1990年以来发生在福建地区及其近海域的地震与地磁异常变化的关系,结果表明,福建沿海地区流动地磁变化与福建省东南沿海及其近海域〉ML4．0级的地震存在较好的对应关系,但对福建省中西部地区映震能力较差。     

吴忠地震窗S值异常与宁夏及邻区中强地震的对应关系

<正>1研究背景地震活动度S（下文简称S值）用于定量描述地震活动性的强弱程度,包括地震频度、平均震级、平均释放能量、最大震级以及地震空间分布的集中度及其记忆效应（谷继成等,1985）。在地震预测实际工作中发现,某些小区域小地震活动与周围中强以上地震活动有一定程度的相关性,即所谓的“地震窗”。将“地震窗”与地震活动度S相结合,研究地震窗内S值异常变化与整个研究区中强地震的对应关系,可以有效开展震情跟踪工作,为震情研判提供参考。本文通过计算吴忠地震窗（下文简称吴忠窗）内小震活动度S,分析宁夏及邻区5级以上地震前S值的变化,探讨窗内S值异常与地震的对应关系。     

运用S方法预测中等地震及小震震群活动性的研究

运用S方法处理流动地磁测量资料，与小震震群地震活动频次对比分析，结果表明流磁测线S值出现异常，一年内小震震群地震活动频次增高；反之，S值较小，则地震活动频次较低；流磁测线S值出现异常，其邻近地区可能发生MS4级左右地震。此方法在少震地区地震的中短期预测中有一定的实用意义。     

冀豫环流动磁测异常与中等地震关系研究

利用冀豫环流动地磁观测资料,绘制单点时序变化曲线,采用常规差值法,计算相邻两期的差值,绘制整个测区的平面等值线;分析研究1998年以来测区周围发生的中等地震与流动地磁数据变化的关系。结果显示,冀豫环流磁异常与邻区的中等地震有一定的对应关系,震前有两个或多个测点同时出现异常,而且异常特征表现为上升正异常。     

“霍山震情窗”动力学背景及预测意义分析

安徽“霍山震情窗”作为华东地区的应力敏感部位,能够以微震、小震活动的形式反映区域应力场的变化。本文基于应变能释放方法对“霍山震情窗”的动力学背景进行了研究,结果表明该震情窗易受青藏块体强震活动的影响,从而出现开窗异常,其异常变幅相对较大;此外,震情窗所处区域应力场的波动变化也会导致开窗异常,其异常变幅则相对较小。上述2 种动力学背景的开窗异常对华东地区中强地震均具有较好的预测意义。此外,在实际应用中应关注多种动力学背景的共同影响可能导致的开窗异常。     

利用地磁低点位移预测发震时间

四川及邻区是未来大震的重点监测地区，为了震情监视分析与预测，对四川地区出现的地磁“低点位移”与四川及邻区的中强地震对应进行了系统研究，认为地磁“低点位移”现象是客观存在的，“低点位移”作为一种地磁异常现象，与地震发生有较好的相关性。     

新疆喀什及邻近区域流动地磁和流动重力联合分析研究

利用2014-2015年南天山地区45个测点的2期流动地磁资料,分析喀什及邻近区域相邻两期岩石圈磁场的动态变化特征,同时,利用2014-2016年170个测点的4期流动重力资料,分析不同时间尺度的重力场动态变化信息。研究表明:皮山6.5级地震的发生对皮山一带的地磁矢量分布特征影响较大,总磁场强度、磁偏角和磁倾角均有变化;无论是半年尺度还是一年尺度的重力变化图像都显示乌恰一直处于重力变化的高梯度带;综合多手段的观测资料对震情形势的判定更为准确。     

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.