A large landslide event in a post‐glacial landscape: rethinking glacial legacy

Threlkeld Knotts (c. 500 m above sea level) in the English Lake District has hitherto been considered to be a glacially‐modified intrusion of microgranite. However, its surface features are incompatible with glacial modification; neither can these nor the subsurface structures revealed by ground‐penetrating radar (GPR) be explained by post‐glacial subaerial processes acting on a glacially‐modified microgranite intrusion. Here we re‐interpret Threlkeld Knotts as a very large post‐glacial landslide involving the microgranite, with an estimated volume of about 4 × 10⁷ m³. This interpretation is tested against published and recent information on the geology of the site, the glacial geomorphic history of the area and newly‐acquired GPR data. More than 60 large post‐Last Glacial Maximum (LGM) rock–slope failures have significantly modified the glaciated landscape of the Lake District; this is one of the largest. Recognition of this major landslide deposit in such a well‐studied environment highlights the need to continuously re‐examine landscapes in the light of increasing knowledge of geomorphic processes and with available technology in currently active or de‐glaciating environments. Copyright © 2012 John Wiley & Sons, Ltd.     

A database for PGA threshold in liquefaction occurrence

Liquefaction exclusion criteria, based on peak ground acceleration (PGA) threshold value, are often included in seismic codes and recommendations. In this note, a rationale approach for setting the threshold is presented and a PGA limit of 0.09 g was found. This value is derived from a statistical analysis of the background data used to create some common verification charts for the liquefaction problem.     

2011年10月12日北京市石景山区M_L2.1地震近场加速度记录初步分析

根据近场强震台加速度记录对2011年10月12日北京市石景山区ML2.1地震的加速度影响场进行了计算分析.同时使用了首都圈宽频带数字台站记录数据通过P波初动格点尝试法解算出该地震的震源机制解,并与加速度影响场进行对比研究.结果表明,此次地震加速度影响场水平向加速度高于垂直向;水平向峰值加速度分布区和加速度影响场高低速度过渡区总体呈EW向或NEE向分布,与震源机制解结果的两个节面走向较为一致;加速度衰减NS向快于EW向.本文研究结果可为强震或较大地震发生后快速判定震害影响场提供参考依据.     

The first peak ground motion attenuation relationships for North of Vietnam

The first attenuation relationships of peak ground acceleration (PGA) and peak ground velocity (PGV) for northern Vietnam are obtained in this study. Ground motion data are collected by a portable broadband seismic network in northern Vietnam as a part of cooperation between the Institute of Geophysics, Vietnamese Academy of Science and Technology, Vietnam and Institute of Earth Sciences, Academia Sinica, Taiwan. The database comprises a total of 330 amplitude records by 14 broadband stations from 53 shallow earthquakes, which were occurred in and around northern Vietnam in the period between 01/2006 and 12/2009. These earthquakes are of local magnitudes between 1.6 and 4.6, focal depths less than 30 km, and epicentral distances less than 500 km. The new attenuation relationships for PGA and PGV are:

log₁₀(PGA)=-0.987+0.7521M_L-log₁₀(R)-0.00475R,     

山东Ⅱ、Ⅲ类场地地震动峰值加速度放大效应分析

利用山东地区实测的Ⅱ类场地358个钻孔和Ⅲ类场地140个钻孔的地震动峰值加速度,计算了各个钻孔不同超越概率的土层地震动峰值加速度的放大系数ks,结果表明:(1)同类场地土层放大系数ks值总体符合正态分布,既有相对集中性,也有离散性;(2)随着基岩面输入地震动强度的增大,ks值降低,且Ⅲ类场地ks值降低较Ⅱ类的更为明显;(3)Ⅱ类场地随着基岩输入面埋深的增加,ks值呈增加趋势,约达20m深后基本趋于稳定,而Ⅲ类场地基岩输入面埋深的增加对ks值的影响不甚显著;(4)Ⅱ类场地50年超越概率10％的平均ks值(1.47)略高于《中国地震动参数区划图》使用的全国平均ks值.本文尝试讨论了山东地区Ⅱ、Ⅲ类场地不同强度基岩峰值加速度输入的ks调整值.     

探索基于地震动峰值加速度的地震灾害评估方法

将福建省面积按0.05°（约5 km）网格离散化后得到4 361个网格点,在地震发生后根据全省台站的监测数据进行计算,每个网格点都能快速得到地震动峰值加速度。利用这些已经赋有地理信息和加速度的网格点对全省乡镇级单位的行政区进行烈度计算和赋值提出一种基于地震动峰值加速度的地震灾害评估方法。     

泰安市岱岳区土地信息监管系统建设

泰安市国土资源局岱岳区分局为了提高监管力度,利用三维可视化、地理信息、遥感影像、场景合成等先进技术,结合大比例尺数字高程模型,合成真实的三维实景环境,与国土资源数据有机融合,实现国土信息的三维再现。构建信息系统监管平台,实现了建设用地审批、供地、利用、补充、检查全过程动态化、精细化管理。在土地行政审批管理中,提高了效率、规范了流程、落实了责任,实现了以图管地的目的。     

北京房山应急水源地地下水数值模拟及河流渗漏量预测

以北京房山岩溶水应急水源地为例,采用等效连续介质体概化地下水流系统,建立地下水流数值模型,评价地下水源汇项,分析地下水系统特征。运用MODFLOW中的河流（渠）子程序包,刻画地表河流和泉水与地下水的交换关系。经参数识别和验证,计算结果与实测数据拟合较好,能够比较准确的模拟水源地岩溶水系统。模拟和预测结果表明,水源地地区地下水与地表水联系密切,应急开采后,地下水系统由向河流排泄转变为河流渗漏补给地下水,可为应急水源地合理开发利用提供科学依据。     

干旱区绿洲城市化发展与耕地保护协同性分析——以张掖市甘州区为例

城市化水平是衡量一个国家经济发达程度,特别是工业化水平高低的一个重要标志,而耕地非农化是城市化过程中的一种必然现象,耕地数量变化体现一定的社会经济发展规律。因此,研究耕地资源与城市化的关系具有一定的现实意义,有助于为当地政府城市规划和进一步发展提供参考依据。处在脆弱敏感的自然环境下,干旱区绿洲城市发展与耕地资源保护存在着显著矛盾。本文基于1996-2008年的统计数据,利用回归分析法和协调度分析法分析了甘州区城市化水平与耕地资源变化的相关性及协调性。结果表明:1996-2002年耕地资源与城市化水平呈现出一定相互促进的正相关关系;2003年耕地资源变化略有波动,耕地面积有所减少。2004-2008年耕地资源变化逐渐趋于平稳,而在此过程中城市化水平一直处于稳步上升状态。协同度除2004年呈不协调状态,其他年份呈基本协调或较协调趋势。     

Seismic random noise attenuation by time-frequency peak filtering based on joint time-frequency distribution

Time-Frequency Peak Filtering (TFPF) is an effective method to eliminate pervasive random noise when seismic signals are analyzed. In conventional TFPF, the pseudo Wigner–Ville distribution (PWVD) is used for estimating instantaneous frequency (IF), but is sensitive to noise interferences that mask the borderline between signal and noise and detract the energy concentration on the IF curve. This leads to the deviation of the peaks of the pseudo Wigner–Ville distribution from the instantaneous frequency, which is the cause of undesirable lateral oscillations as well as of amplitude attenuation of the highly varying seismic signal, and ultimately of the biased seismic signal. With the purpose to overcome greatly these drawbacks and increase the signal-to-noise ratio, we propose in this paper a TFPF refinement that is based upon the joint time-frequency distribution (JTFD). The joint time-frequency distribution is obtained by the combination of the PWVD and smooth PWVD (SPWVD). First we use SPWVD to generate a broad time-frequency area of the signal. Then this area is filtered with a step function to remove some divergent time-frequency points. Finally, the joint time-frequency distribution JTFD is obtained from PWVD weighted by this filtered distribution. The objective pursued with all these operations is to reduce the effects of the interferences and enhance the energy concentration around the IF of the signal in the time-frequency domain. Experiments with synthetic and real seismic data demonstrate that TFPF based on the joint time-frequency distribution can effectively suppress strong random noise and preserve events of interest.