浅谈芦山地震

地震序列是对地震现象的回顾性描述,只有在地震序列结束后它才有可能被确切无疑地判定.鉴于龙门山断裂带或地震带的整体性、统一性和系统性,不可否认在其西南段发生的芦山地震是与汶川地震一样的同属于龙门山断裂带的事件.鉴于芦山地震的震源位置、震源机制、震级大小和破裂区覆盖的范围,目前可认为它是汶川地震迄今最大的余震.鉴于地震序列的判定是对地震现象的唯象的描述,有相当的任意性,对芦山地震究竟是"新的主震"还是"汶川余震"的"讨论"实质上是在根据经验判定地震的类型,即使目前看"主震说"提出的4条"论据"明显缺乏说服力,"余震说"比较有说服力,但最后都需要等到地震序列结束之后才有可能"定论".作者认为,相对于需要等到地震序列结束之后才能"定论"、甚而在地震序列结束之后未必能"定论"的芦山地震究竟是"新的主震"还是"汶川余震"问题,应当更为关注芦山地震的发生引出的一些重要的亟待研究的科学问题与防震减灾问题.     

Assessment of sediment transport approaches for sand-bed rivers by means of machine learning

Abstract

The quantification of the sediment carrying capacity of a river is a difficult task that has received much attention. For sand-bed rivers especially, several sediment transport functions have appeared in the literature based on various concepts and approaches; however, since they present a significant discrepancy in their results, none of them has become universally accepted. This paper employs three machine learning techniques, namely artificial neural networks, symbolic regression based on genetic programming and an adaptive-network-based fuzzy inference system, for the derivation of sediment transport formulae for sand-bed rivers from field and laboratory flume data. For the determination of the input parameters, some of the most prominent fundamental approaches that govern the phenomenon, such as shear stress, stream power and unit stream power, are utilized and a comparison of their efficacy is provided. The results obtained from the machine learning techniques are superior to those of the commonly-used sediment transport formulae and it is shown that each of the input combinations tested has its own merit, as they produce similarly good results with respect to the data-driven technique employed.

Editor Z.W. Kundzewicz     

基于有限断层模型的芦山“4·20”7.0级强烈地震强地面运动特征

基于芦山地震的震源破裂过程反演结果,利用有限断层模型,以芦山地区三维地壳速率结构模型为基础,对芦山“4·20”7.0级强烈地震引起的强地面运动进行了模拟.对这次地震中由典型盲断层引起的强地面运动数值模拟结果反映了与实际震害相近的分布特征:断层上盘的宝盛、龙门及芦山以北位于极震区,也是强地面运动的高强度集中区,特别是垂向分量的速度、加速度峰值均在该地区达到了最大值,最能反映地表震害特征的竖向地震加速度在龙门一带达到了350gal,与极震区Ⅸ度的烈度相当,而在芦山以北龙门一带,瞬时竖向位移峰值高达110cm,这些特征与实际震害分布是非常相近的.综合分析认为,这次地震强地面运动表现出了明显的逆冲断层引起的强地面运动的分布特征,同时在强地震动传播过程中,由于高陡峭地形地貌特征及四川盆地内山间盆地的影响,地形地貌和盆地效应对地震波的反射和放大作用明显加强,也是该地区地震破坏强度增大的重要因素.     

震源动力学破裂过程数值模拟研究

首先阐述了震源动力学过程研究的重要意义, 在此基础上, 研究了复杂的断层几何形态及介质模型对动力学破裂过程的影响, 并对常用的有限元方法、 离散元方法、 有限差分方法和边界积分方程方法等进行了相应介绍. 讨论了这些数值模拟方法各自的优缺点, 建议在方法的选择上应视具体问题及计算的精度而定. 最后对动力学数值模拟的关键部分, 滑动摩擦准则进行了论述. 常用的滑动摩擦准则有滑动弱化准则、 速率弱化准则和速率-状态依赖摩擦准则. 在单纯考虑某个地震的动力学破裂传播过程时, 滑动弱化准则较为常用, 其中滑动弱化距离的选取至关重要. 但若考虑整个地震循环, 速率-状态依赖摩擦准则更为合适.      

Adaptive neural-based fuzzy inference system (ANFIS) approach for modelling hydrological time series

Abstract

The main aim of this study is to develop a flow prediction method, based on the adaptive neural-based fuzzy inference system (ANFIS) coupled with stochastic hydrological models. An ANFIS methodology is applied to river flow prediction in Dim Stream in the southern part of Turkey. Application is given for hydrological time series modelling. Synthetic series, generated through autoregressinve moving-average (ARMA) models, are then used for training data sets of the ANFIS. It is seen that the extension of input and output data sets in the training stage improves the accuracy of forecasting by using ANFIS.     

Biosorption of Heavy Metals in Leachate Derived from Gold Mine Tailings Using Aspergillus fumigatus

Leachate derived from bioleaching process contains high amount of metals that must be removed before discharging the water. Aspergillus fumigatus was isolated from a gold mine tailings and its ability to remove of As, Fe, Mn, Pb, and Zn from aqueous solutions and leachate of bioleaching processes was assessed. Batch sorption experiments were carried out to characterize the capability of fungal biomass (FB) and iron coated fungal biomass (ICFB) to remove metal ions in single and multi‐solute systems. The maximum sorption capacity of FB for As(III), As(V), Fe, Mn, Pb, and Zn were 11.2, 8.57, 94.33, 53.47, 43.66, and 70.4 mg/g, respectively, at pH 6. For ICFB, these values were 88.5, 81.3, 98.03, 66.2, 50.25, and 74.07 mg/g. Results showed that only ICFB was found to be more effective in removing metal ions from the leachate. The amount of adsorbed metals from the leachate was 2.88, 21.20, 1.91, 0.1, and 0.08 mg/g for As, Fe, Mn, Zn, and Pb, respectively. The FT‐IR analysis showed involvement of the functional groups of the FB in the metal ions sorption. Scanning electron microscopy revealed that surface morphological changed following metal ions adsorption. The study showed that the indigenous fungus A. fumigatus was able to remove As, Fe, Mn, Pb, and Zn from the leachate of gold mine tailings and therefore the potential for removing metal ions from metal‐bearing leachate.     

芦山4.20地震破裂过程及其致灾特征初步分析

采用全球地震台网的远震地震波数据快速反演了2013年4月20日雅安芦山地震(芦山4.20地震)的破裂过程,在震后3小时得到并发布了相关测定结果.结果显示这次地震的震级约M_W6.8,包括两次破裂子事件,但都发生在断层面上震源(破裂起始点)附近,整个地震没有表现出明显的破裂方向性.雅安芦山地震的破裂没有大规模出露地表,主要地震灾害集中在断层上盘,位于芦山县和宝兴县一带.     

一种基于紫外极光图像的亚暴膨胀期起始时刻的自动检测方法

准确界定亚暴起始时刻是理解亚暴相关问题的关键.已有研究主要集中在两方面:一是从极光图像中人工挑选亚暴事件进行案例分析或统计分析来研究亚暴发生机制及亚暴期间的地磁环境;二是基于一些空间物理参数,如AE指数、SME(SuperMAG electrojet)指数、Pi2、正弯扰等,采用人眼判断或是模式识别的方法从中找出亚暴起始时刻.本文尝试采用模式识别的方法从紫外极光图像中自动地检测出亚暴膨胀期起始时刻.首先,将紫外极光图像通过网格化处理转换到磁地方时-地磁纬度(MLT-MLAT)直角坐标下,然后通过模糊c均值聚类方法提取亮斑,再考察亮斑强度是否增强、面积是否极向膨胀来判断是不是亚暴事件.本文方法在1996年12月-1997年2月这三个月的Polar卫星紫外极光图像上进行了实验验证.我们将检测到的亚暴起始时刻与Liou(J. Geophys. Res., 2010, 115: A12219)的人工标记进行了对比,并详细分析了与标记不一致的多检和漏检事件.本文提出的自动检测方法可以快速地从海量紫外极光图像中完成亚暴事件的初步筛选,方便研究人员进一步深入研究极光亚暴.     

IMPACT OF THE SOUTHERN OSCILLATION ON THE NORTH AMERICAN SOUTHWEST MONSOON

The intensity and spatial variations in the North American Southwest Monsoon are examined to determine the influence of the Southern Oscillation. Sixty-five years (1920–1984) of July and August monthly precipitation data from Arizona and New Mexico are normalized using a square root transformation, converted into z-scores, and stratified according to onset and following years for Warm Events and Cold Events of the Southern Oscillation. The results for July reveal different spatial patterns in the monsoonal precipitation for the extremes of the Southern Oscillation. Warm-Event onset years are associated with positive precipitation anomalies that decline along a northeast-to-southwest gradient across the study area whereas the Cold-Event onset years produce highest positive values in west-central Arizona and negative values throughout the eastern two-thirds of the study area. Spatial patterns for the August precipitation data do not appear to be influenced by the extremes of the Southern Oscillation. [Key words: Southwest Monsoon, Southern Oscillation, Arizona, New Mexico.]     

基于过程的面向对象时空数据模型数据组织方法

本文在分析现有时空数据模型和面向对象方法的基础上,提出了基于过程的面向对象时空数据模型,该模型从时空语义建模的角度反映空间对象的演变过程,以及在这个过程中产生的事件因果联系,并且通过过程语义和面向对象思想两者的结合解决了时空动态数据的组织、存储和查询问题。