红山地震台面波震级Ms的研究

本文选用了红山地震台ＤＫ－１测震记录仪记录到的１９８７年－１９９０年Ｍｓ≥４．８地震共１１６４次，这些地震分布在全球各个区域，我们参照国家地震局地球物理研究所编篡的＜＜中国地震台临时报告＞＞中的震级以及有关资料，对红山地震台所测定的面波震级Ｍｓ进行了对比，讨论。结果认为红山地震台以往测定的面波震级基本合理，对于６级以上地震震级相对偏差较大；通过震中距△分区间深入研究，我们给出了每个区间的面波震级台     

岫岩5.4级地震前后振幅比变化特征

1999年11月29日，辽宁省岫岩发生了Ms5．4地震，本文研究了该地震前后岫岩、营口、丹东、本溪、宽甸、东陵六个数字化地震台记录的数字地震波振幅比的变化特征。并通过分析S波、P波振幅关系探讨了岫岩地震前后震源机制的变化。结果表明：岫岩5．4级地震前，营口、本溪、丹东、东陵四个台在震前都出现低值异常现象；岫岩5．1级地震前，岫岩、本溪、丹东、东陵四个台震前均出现低值现象。岫岩5．4级前震序列P波最大振幅与S波最大振幅显示出较好的线性关系，但余震序列P波最大振幅与S波最大振幅则较为离散，呈非线性关系。     

2001年11月14日昆仑山口西M 8.1地震前的缓慢地震事件

2001年11月14日昆仑山口西M8．1地震前发生了缓慢运动事件，新疆地震台网记录分析结果表明，这次事件在大震前3．5天开始出现，长周期前驱波持续约47小时，波列呈现规则的正弦波形，视周期约为8．8秒。笔者认为，该慢地震事件是M8．1大震前中昆仑断裂临震预滑动引起的。事实表明，慢地震的观测与研究对深入了解断层失稳过程和实现地震短临预报具有重大意义，同时也显示了宽频带数字地震台网的优越性。     

托来6.0级地震前波速比异常与中短期预报指标讨论

本文阐述了１９９３年１０月２６日青海托来６．０级地震前河西祁连山中西部的波连比异常并进一步讨论了中短期预报指标。通过托来地震研究得到，波速比低值集中区边缘与低波速比异常值地震条带交汇区可能为未来主震位置，波速比低值在多次中强震后仍然继续异常以及波速比在震前１─６个月显著回升可分别作为较强地震趋势异常和地震发生的短期指标。     

乌鲁木齐及附近地区剪切波分裂特征研究

利用S波分裂的方法，分析了2003年2月14日新疆石河子5．4级地震前后多台所记录的小地震的S波分裂特征，发现震源附近地区的S波分裂特征对中强震仍有一定的前兆意义．震中附近的3个地震台记录的S波偏振方向在5．4级地震前出现由原来与区域应力场一致的NE向转为NW向震后又转回NE向。5．4级地震前各台记录的慢波延迟时间总体表现出由小变大的特征．     

DK1地震仪的面波震级起算函数研究di

使用1987～1993年DK1地震仪的地震记录，以国际地震中心(ISC)MS震级为标准震级，根据误差理论用最小二乘法拟合导出DK1地震仪面波震级起算函数．又从起算函数物理意义出发，根据成层介质中面波传播理论，考虑到地震波的频散、介质的吸收、地球介质与DK1地震仪所组成的线性滤波器对面波振幅和周期的影响，并假定面波最大振幅对应于Airy相，导出了DK1地震仪测定面波震级的起算函数． 使用本文导出的起算函数，不附加任何校正值．通过315个地震，对36个速报台的单台DK1面波震级和DK1速报台网的面波震级测定误差检验，结果表明，DK1面波震级MS(DK1)与国际地震中心(ISC)相应地震面波震级MS(ISC)之间在统计上无系统误差，平均误差接近于零．      

成都地震台网对印度洋特大地震面波震级的复测--面波震级都会饱和吗

对于2004年12月26日印度洋大地震，成都地震遥测台网有宽频带数字地震记录波形没有出格，测定的面波震级为9．0。这对于通常人们认为面波震级超过8．6可能出现饱和是一个值得注意和研究的现象。     

地震面波产生的地震动转动分量研究

本文利用弹性波动理论对地面转动分量，即瑞利（Rayleigh)波和乐夫（Love)波产生的转动分量进行了研究，给出了相应的计算公式和计算方法，特别注意到面波的散射效应对转动分量的影响，并将这一特性引入到转动分量的求取中，使问题的解决更切合于实际，最后选取实际地震记录，利用得到的公式计算出地震面波产生的转动分量。     

汶川地震前后地震波速比和视速度变化特征的研究

2008年5月12日在中国四川省境内龙门山断裂带发生了8级巨大地震．在其主震前后随着震源区附近应力状态的改变,地壳介质的物性是否也存在相应的异常变化过程？该问题成为汶川地震研究的热点科学问题之一．本研究搜集和整理了中国地震局四川数字地震台网2001年1月1日-2010年5月31日产出的震相观测报告,和中国地震局地球物理研究所流动数字地震台网2008年5月12日——9月30日产出的震相观测报告,采用多台和达法和多地震联合测定法,根据入选的直达波Pg和Sg的震相数据,重点研究了龙门山断裂及其附近地区的P波和S波视速度的时间变化特征,并与波速比的时间变化特征进行了对比分析．为保证计算结果的可靠性和稳定性,对所收集到的数据进行了较为严格的筛选和限定．研究发现,龙门山断裂及其附近地区,在汶川地震前P波和S波视速度存在4年左右的明显降低过程,到震前约半年出现快速恢复．在震前P波和S波的视速度明显降低的过程中,波速比的低值异常过程仅为2年多,且幅度小持续时间较短．在波速比和视速度异常发展的进程中,进入发震中短期异常快速恢复是两者的共同特征．      

大震前P波出射角和方位角的异常变化

给出了数字化地震记录Ｐ波初始部分平均出射角和方位角的分析处理方法，研究了山西大同Ｍｔ＝６．１级地震以及唐山Ｍｔ＝５．６级地震前出射角与方位角出现的异常变化，并对地震前地震波动力学特征的这一类前兆异常现象进行了初步讨论。     

Uncertainty Analysis of Strong-Motion and Seismic Hazard

In this article we present the modelling of uncertainty in strong-motion studies for engineering applications, particularly for the assessment of earthquake hazard. We examine and quantify the sources of uncertainty in the basic variables involved in ground motion estimation equations, including those associated with the seismological parameters, which we derive from a considerable number of strong-motion records. Models derived from regression analysis result in ground motion equations with uncertain parameters, which are directly related to the selected basic variables thus providing an uncertainty measure for the derivative variable. These uncertainties are exemplified and quantified. An alternative approach is presented which is based on theoretical modelling defining a functional relationship on a set of independent basic variables. Uncertainty in the derivative variable is then readily obtained when the uncertainties of the basic variables have been defined. In order to simplify the presentation, only the case of shallow strike-slip earthquakes is presented. We conclude that the uncertainty is approximately the same as given by the residuals typical for regression modelling. This implies that uncertainty in ground motion modelling cannot be reduced below certain limits, which is in accordance with findings reported in the literature. Finally we discuss the implications of the presented methodology in hazard analyses, which is sensitive to the truncation of the internal error term, commonly given as an integral part of ground motion estimation equations. The presented methodology does not suffer from this shortcoming; it does not require truncation of the error term and yields realistic hazard estimates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluating the performance of topobathymetric LiDAR to support multi-dimensional flow modelling in a gravel-bed mountain stream

Stream biophysical processes are commonly studied using multi-dimensional numerical modelling that quantifies flow hydraulics from which parameters such as habitat suitability, stream carrying capacity, and bed mobility are derived. These analyses would benefit from accurate high-resolution stream bathymetries spanning tens of kilometres of channel, especially in small streams or where navigation is difficult. Traditional ground-based survey methods are limited by survey time, dense vegetation and stream access, and are usually only feasible for short reaches. Conversely, airborne topobathymetric LiDAR surveys may overcome these limitations, although limited research is available on how errors in LiDAR-derived digital elevation models (DEMs) might propagate through flow models. This study investigated the performance of LiDAR-derived topobathymetry in support of multi-dimensional flow modelling and ecohydraulics calculations in two gravel-bedded reaches (approximately 200 m long), one morphologically complex and one morphologically simple, and at the segment scale (32 km-long stream segment) along a 15 m-wide river in central Idaho, USA. We compared metre and sub-metre-resolution DEMs generated from RTK-GPS ground and Experimental Advanced Airborne Research LiDAR-B (EAARL-B) surveys and water depths, velocities, shear stresses, habitat suitability, and bed mobility modelled with two-dimensional (2D) hydraulic models supported by LiDAR and ground-surveyed DEMs. Residual statistics, bias (B), and standard deviation (SD) of the residuals between depth and velocity predicted from the model supported by LiDAR and ground-survey topobathymetries were up to −0.04 (B) and 0.09 m (SD) for depth and −0.09 (B) and 0.20 m s⁻¹ (SD) for velocity. The accuracy (B = 0.05 m), precision (SD = 0.09 m), and point density (1 point m⁻²) of the LiDAR topobathymetric survey (regardless of reach complexity) were sufficient to support 2D hydrodynamic modelling and derivative stream habitat and process analyses, because these statistics were comparable to those of model calibration with B = 0 m and SD = 0.04 m for water surface elevation and B = 0.05 m s⁻¹ and SD = 0.22 m s⁻¹ for velocity in our investigation. © 2020 John Wiley & Sons, Ltd.     

Empirical assessment of flood wave celerity–discharge relationships at local and reach scales

ABSTRACT

An accurate comprehension of celerity (flood wave speed) dynamics is a key step for understanding flood wave propagation in rivers. We present the results of empirically estimated celerity values in 12 Brazilian rivers, and analyse the behaviour of celerity–discharge relationships (CxQ). Celerity was estimated with a reach-scale (RS) method, based on the peak travel time between stations; and with a local-scale (LS) method, based on the derivative of discharge–cross-section area relationships surveyed at gauging stations. The results indicate that the magnitudes of celerity values obtained by the methods are reasonably comparable, and can rarely be considered constant, varying with river discharge. Three reaches presented differing CxQ relationships at local and reach scales, which suggests that in situ cross-sections at gauging stations should not be extrapolated as representative of the whole reach for flood routing studies, and that CxQ relationship assessments might provide relevant insights for hydrological modelling.     

Hydraulic modelling of Athabasca Vallis,Mars

Abstract

Palaeohydraulic modelling is presented for Athabasca Vallis, the youngest known catastrophic flood channel on Mars. This modelling incorporates three significant advantages over previous modelling of Martian channels: a step-backwater hydraulic model; more accurate topography; and improved flood height indicators. The maximum modelled palaeodischarge is between 1 × 10⁶ and 2 × 10⁶m³s^?1 depending on the friction coefficient selected. An anomalously high palaeostage indicator suggests a region of ponded backwater in the channel in which streamlined forms were created through deposition, with the additional possibility of post-flood subsidence/lowering of the channel slope due to magma extrusion.     

An examination of geochemical modelling approaches to tracing sediment sources incorporating distribution mixing and elemental correlations

The identification of sediment sources is fundamental to the management of increasingly scarce water resources. Tracing the origin of sediment with elemental geochemistry is a well‐established approach to determining sediment provenance. Fundamental to the confident apportionment of sediment to their lithogenic sources is the modelling process. Recent approaches have incorporated distributions throughout the modelling process including source contribution terms for two end‐member sources. The shift from modelling source samples to modelling samples drawn from distributions has removed relationships, including potential correlations between elemental concentrations, from the modelling process. Here, we present a novel modelling approach that re‐incorporates correlations between elemental concentrations and models distributions for source contribution terms for multiple source end members. Artificial mixtures, based on catchment sources samples, were created to test the accuracy of this correlated distribution model and also examine modelling approaches used in the literature. The most accurate model incorporates correlations between elements, uses the absolute mixing model difference and does not use any weighting. This model was then applied to identify the sources of sediment in three South East Queensland catchments and demonstrated that Quaternary Alluvium is the most dominant source of sediment in these catchments (μ 44%, σ 12%). This study demonstrates that it is important to understand how different weightings may impact modelling results. Copyright © 2014 John Wiley & Sons, Ltd.     

MAGNETOTELLURIC MODELLING BY THE FINITE ELEMENT METHOD*

The finite element method, here viewed as a special case of the Galerkin projective method, is applied to the modelling of magnetotelluric problems, and its adaptation to geological profiles is outlined. A novel method for obtaining surface field values, involving matrix representation of the normal derivative operator, is presented in detail. Results obtained by this method are compared with well-known infinite series solutions for the vertical fault and the outcropping dyke. Two profiles containing sulphide zones are also modelled, the results being compared with field data; satisfactory agreement is obtained.     

Bayesian modelling of environmental risk: example using a small area ecological study of coronary heart disease mortality in relation to modelled outdoor nitrogen oxide levels

Bayesian modelling of health risks in relation to environmental exposures offers advantages over conventional (non-Bayesian) modelling approaches. We report an example using research into whether, after controlling for different confounders, air pollution (NO_x) has a significant effect on coronary heart disease mortality, estimating the relative risk associated with different levels of exposure. We use small area data from Sheffield, England and describe how the data were assembled. We compare the results obtained using a generalized (Poisson) log-linear model with adjustment for overdispersion, with the results obtained using a hierarchical (Poisson) log-linear model with spatial random effects. Both classes of models were fitted using a Bayesian approach. Including spatial random effects models both overdispersion and spatial autocorrelation effects arising as a result of analysing data from small contiguous areas. The first modelling framework has been widely used, while the second provides a more rigorous model for hypothesis testing and risk estimation when data refer to small areas. When the models are fitted controlling only for the age and sex of the populations, the generalized log-linear model shows NO_x effects are significant at all levels, whereas the hierarchical log-linear model with spatial random effects shows significant effects only at higher levels. We then adjust for deprivation and smoking prevalence. Uncertainty in the estimates of smoking prevalence, arising because the data are based on samples, was accounted for through errors-in-variables modelling. NO_x effects apparently are significant at the two highest levels according to both modelling frameworks.

A wavelet-neural network hybrid modelling approach for estimating and predicting river monthly flows

Abstract

A wavelet-neural network (WNN) hybrid modelling approach for monthly river flow estimation and prediction is developed. This approach integrates discrete wavelet multi-resolution decomposition and a back-propagation (BP) feed-forward multilayer perceptron (FFML) artificial neural network (ANN). The Levenberg-Marquardt (LM) algorithm and the Bayesian regularization (BR) algorithm were employed to perform the network modelling. Monthly flow data from three gauges in the Weihe River in China were used for network training and testing for 48-month-ahead prediction. The comparison of results of the WNN hybrid model with those of the single ANN model show that the former is able to significantly increase the prediction accuracy.

Editor D. Koutsoyiannis; Associate editor H. Aksoy

Citation Wei, S., Yang, H., Song, J.X., Abbaspour, K., and Xu, Z.X., 2013. A wavelet-neural network hybrid modelling approach for estimating and predicting river monthly flows. Hydrological Sciences Journal, 58 (2), 374–389.     

Representation of radiation damping by fractional time derivatives

When modelling unbounded domains, formulation of a matrix‐valued force–displacement relationship which can take radiation damping into account is of major importance. In this paper, a method to describe the dynamic stiffness by a system of fractional differential equations in the time‐domain is presented. Here, a doubly asymptotic rational approximation of the low‐frequency force–displacement relationship is used, whereas a direct interpretation of the asymptotic part as a fractional derivative is possible. The numerical solution of the corresponding system of fractional differential equations is demonstrated using the infinite beam on elastic foundation as an example. Copyright © 2003 John Wiley & Sons, Ltd.