山西省数字台网与模拟台网震级的对比研究

统计分析了山西省数字地震台网考核运行 3个月以来的记录地震的震级情况 ,将两套人机交互处理系统 (泰德和港震系统 )测定的速度震级及港震系统仿真后 (DD— 1)测得的位移震级 ,与山西省模拟台网 (即大同、太原、临汾、长治 9个模拟人工值守台 )所测定的位移震级进行了对比 ,研究了它们之间的相关程度、一致性、差异性 ,得出港震系统与泰德系统测定的速度震级与模拟震级、数字系统仿真 (DD— 1)后测定的位移震级与模拟震级相关系数均在 0 .940以上 ,相关性较好的结论     

用河北张家口台速度与位移记录测定近震震级的对比

对河北张家口台FBS-3宽频带大动态范围的数字化速度地震仪和DD—2短周期模拟位移地震仪所记录的河北张北地区的地震，利用速度和位移数据分别测定了近震震级并进行了对比分析。结果显示，在一定的震级范围内，这两种资料测定的震级基本一致，没有发现二者之间存在系统误差，标准误差也较小。可以认为，无论从其物理意义还是具体做法上，用速度测定的震级与由位移测定的震级之间能够保持较好的一致性和连续性。     

天津遥测地震台网MD震级偏差分析

本文介绍了天津遥测地震台网M_D震级测定方法和测定精度,根据1987—1989年震级测定资料统计分析了本台网M_D相对于北京台网、河北台网和分析预报中心全国地震月报目录M_L震级的偏差,同时对本台网M_D和M_L测定震级偏差进行了比较,并对结果作了初步讨论和分析。     

连云港单台测定m_b震级偏差分析

选取2013—2014年连云港地震台单台测定的m_b震级,以中国地震台网中心公布的相应地震震级为标准震级,分析震级偏差平均值、震级大小、震中距、震中方位对震级偏差的影响,并利用稳健回归方法给出震级校正关系式。结果发现:单台震级比中国地震台网中心公布的震级低0.05级;对于中强地震,二者测定结果基本一致;震级偏差随震中距增大逐渐减小,且EN向地震震级偏差较大;采用稳健回归方法校正震级与中国地震台网中心公布震级偏差较小,比较精确。     

鹤岗地震台面波震级偏差分析

在地震震级国家标准《地震震级的规定》(GB17740—2017)发布以后,收集整理鹤岗地震台2018年1月—2020年3月测定的远震面波震级M_(S(HEG)),与中国地震台网中心地震目录中给定的面波震级M_(S(CENC))进行比较,统计二者偏差值。利用统计学方法,分析震级偏差与震级、震中距和反方位角的关系。结果表明:与中国地震台网中心地震目录发布震级相比,鹤岗地震台测定的面波震级偏高,且震级偏差与震中距表现为正相关性;震中位于鹤岗地震台站西北方位,震级偏差较小,而在其他方位,震级偏差则较大。     

连云港地震台面波震级偏差分析

整理2013—2014年连云港地震台测定的地震MS震级,与中国地震台网中心公布震级进行对比,统计两者震级偏差平均值,并分析震级偏差与震级大小、震中距、震中方位的关系。结果表明:连云港地震台MS震级比中国地震台网中心低0.22,且震级偏差随震中距的增大逐渐减小;地震震中不同,震级偏差均表现为负值,震中方位在东北和西北方向,震级偏差最大,为-0.24,西南方向偏差最小,为-0.2。     

江苏及邻区地方性震级量规函数的研究

基于2009～2018年江苏及相邻数字地震台网记录的2602次地震事件观测资料,通过震级残差统计方法得到了72个台站的单台震级与台网平均震级的偏差、平均偏差和标准偏差,分析了震级偏差频次分布和定量统计结果,进而修正了江苏及邻区的地方性震级量规函数。实际地方性震级测定结果表明,使用校正后的量规函数比新震级国家标准(GB17740—2017)中量规函数所测定的震级的标准差更小,且单台震级残差相对更集中于0,这说明该量规函数有助于提高江苏及邻区地方性震级测定精度。     

江西测震台网新、旧震级国家标准测定地方性震级的对比分析

选用了2011—2018年的江西数字地震台网的地震观测资料,重新测定地方性震级ML,并通过统计分析方法进行对比,得到如下结论:使用分区量规函数的新震级国标下的ML与使用全国统一量规函数的ML的差值很小,约有95%的震级偏差在0.1级以内,因此,推行新震级国标能够与原有地方性震级很好的衔接;使用分区量规函数测定的ML单台震级偏差和平均标准偏差值都更小,说明使用新震级国标测定的ML更精确。     

现今震级测定偏差

本文着重讨论世界主要地震机构测定震级偏差分布情况。用“震级均等率”和“震级偏差率”的数值，表示对包括我国台网，美国台网，俄罗斯台网和日本气象厅台网震级偏差的总评价。     

赤峰及邻区地方性震级量规函数修正

选取2010—2019年赤峰市及邻区发生的884次地方震，针对该区域10个地震台站记录的5 160个地震事件，基于残差统计方法，得到各台站单台震级与中国地震台网中心发布震级的偏差、平均偏差和标准偏差，得出单台震级平均偏差随震中距的变化，进而修正研究区域地方性震级量规函数，并予以验证。结果表明，使用修正后量规函数计算的标准差（0.284）小于由原量规函数计算的标准差（0.356），且所得震级偏差分布较由原量规函数所得结果更集中，说明应用修正量规函数测定赤峰及邻区地方性震级更准确。     

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.