Q c of three component seismograms of volcanic microearthquakes at Campi Flegrei volcanic area — Southern Italy

Digital recordings of three component microearthquake codas from shallow seismic events in the volcanic region of Campi Flegrei — Southern Italy — were used with an automatic technique to calculate the attenuation factorQ _c (codaQ) in the hypothesis of singleS toS backscattering.Results show the same value ofQ for each of the three components. This result is interpreted as due to isotropicS wave radiation pattern.A check of the coda method was performed using a single station method based on simple assumptions on the direct SH wave spectrum. Single stationQ was averaged over the stations and over the earthquakes. Results show that the two methods lead to comparable results.A frequency dependence quite different from that evaluated in active tectonic regions was found for coda attenuation, comparable to other volcanic areas throughout the world. This is interpreted as due to the presence of magma that affects anelasticity and scattering.     

基于虚拟地理环境的游戏化学习系统与应用

游戏化学习是将计算机游戏应用于教学的一种新的教育手段,相比于传统的课件教学方式,使用虚拟沙盒更能培养学生的动手能力和团队协作能力,甚至能让学生参与游戏化课件的制作与完善。基于虚拟沙盒构建的虚拟地理环境能为地学知识的游戏化学习提供充分的技术条件,为地学知识教学提供了新的方式。大陆漂移模拟、溶洞现象模拟和矿物晶体虚拟仿真等典型应用体现了基于虚拟地理环境的游戏化学习系统的典型特征。     

Constructing Community Through Maps? Power and Praxis in Community Mapping*

Despite the growing practice of community mapping, empirical research remains limited. Extant studies have focused primarily on “counter‐maps” and indigenous maps, leaving many locally produced maps and their authors' perspectives unexplored. This article identifies the mapping process as critical to the definition and understanding of community mapping. It links critical cartography literature to goals of community‐mapping practitioners through themes of inclusion, transparency, and empowerment. The discussion highlights the social construction and practice of “community,” the relationship between maps and power, the definitional difficulties associated with community mapping, and the figurative and literal boundaries that constrain community cartography. Finally, it points to areas for further research and exploration.     

The Hydro-Mechanically Coupled Response of Rock Fractures

Summary. In a fractured rock mass, variations in stress and fluid pressure induced by engineering activities can significantly affect the hydrogeological properties. A significant change in fracture transmissivities can also be experienced in the far-field. The simulation of this kind of change requires a Hydro-Mechanical (HM) coupled model. The purpose of this paper is to show how such a model can be used to analyse the evolution of deformation and pressure in a fracture subjected to fluid injection. A 2D BEM-FEM code is used to solve the non-linear system of equations that describe the dependency of transmissivity on local fracture closure. The results of a sensitivity analysis of the essential fracture parameters allow one to gain insight into the importance of the HM models in the framework of the hydrogeology of fractured rock masses. Results obtained from a system of two impervious blocks and a saturated fracture are reported, in order to show the possibilities offered by this technique.     

基于小波的被动声纳降噪研究

基于小波的降噪理论,研究了水下舰船辐射噪声的被动声纳降噪问题。通过对船辐射噪声的建模和仿真,分析对比了不同方法对舰船辐射噪声信号降噪的效果,并利用各种小波基和采用不同阈值条件下对信号进行降噪处理的效果。该研究在分析对比的基础上,进行小波包软阈值去噪并且取得了较好的效果,对被动声纳降噪提供了较好的应用前景。     

一万年以来凉山地区气候变迁

利用地层沉积物孢粉分析成果和相关文献记载复原一万年以来凉山地区的气候状况,并分析了历史时期凉山地区气候变迁的规律:凉山地区一万年以来气候变化大致可分为8个时期,其间气候有冷暖干湿的变化.气温的变化幅度在1℃～2℃,垂直气候带有上升和下降的变化,升降幅度在200～400 m之间.一万年以来凉山地区气候变化的总体趋势与内地大体一致,但在具体时段上有一定差异,气温虽有冷暖的变化,但总体上气温比内地略为温暖.     

基于动力可靠度的隔震结构参数模糊优化

分别选取Bouc—Wen和退化Bouc—Wen模型描述隔震层及上部结构滞变回复力，采用虚拟激励法进行隔震结构随机响应分析。用各层最大层间位移响应和累计疲劳损伤指数建立双参数的功能状态方程，用一次二阶矩理论计算隔震结构失效概率。选用一个隔震框架作为数值算例，探讨了低频过滤器、隔震阻尼比和隔震刚度对隔震结构各子系统条件失效概率的影响。建立了隔震结构参数多目标优化模型，用失效概率确定单因素评判的隶属度，并采用最大隶属度法对隔震参数进行模糊优化。     

Prediction of elastic displacement response spectra in Europe and the Middle East

Empirical equations are presented for the prediction of displacement response ordinates for damping ratios of 2, 5, 10, 20 and 30% of critical and for response periods up to 4s, using 532 accelerograms from the strong‐motion databank from Europe and the Middle East. The records were all re‐processed and only employed for regressions at periods within the usable range, defined as a fraction of the filter cut‐off and depending on the instrument type (digital or analogue), earthquake magnitude and site class. The equations can be applied to predict the geometric mean displacement and pseudo‐acceleration spectra for earthquakes with moment magnitudes ( M ) between 5 and 7.6, and for distances up to 100km. The equations also include style‐of‐faulting and site class as explanatory variables. The predictions obtained from these new equations suggest that earlier European equations for spectral displacements underestimate the ordinates at longer periods as a result of severe filtering and the use of the spectral ordinates at periods too close to the filter cut‐off. The results also confirm that the period defining the start of the constant displacement plateau in the Eurocode 8 (EC8) spectrum is excessively short at 2s. The results not only show that the scaling factor defined in EC8 for estimating the spectral ordinates at damping ratios different from 5% of critical are a good general approximation, but also that this scaling varies with magnitude and distance (reflecting the influence of duration) and also displays a mild dependence on response period. Copyright © 2007 John Wiley & Sons, Ltd.     

Probabilistic estimation of maximum inelastic displacement demands for performance‐based design

A probabilistic approach to estimate maximum inelastic displacement demands of single‐degree‐of‐freedom (SDOF) systems is presented. By making use of the probability of exceedance of maximum inelastic displacement demands for given maximum elastic spectral displacement and the mean annual frequency of exceedance of elastic spectral ordinates, a simplified procedure is proposed to estimate mean annual frequencies of exceedance of maximum inelastic displacement demands. Simplifying assumptions are thoroughly examined and discussed. Using readily available elastic seismic hazard curves the procedure can be used to compute maximum inelastic displacement seismic hazard curves and uniform hazard spectra of maximum inelastic displacement demands. The resulting maximum inelastic displacement demand spectra provide a more rational way of establishing seismic demands for new and existing structures when performance‐based approaches are used. The proposed procedure is illustrated for elastoplastic SDOF systems having known‐lateral strength located in a region of high seismicity in California. Copyright © 2007 John Wiley & Sons, Ltd.     

基于二十面体剖分格网的球面实体表达与Voronoi图生成

在分析当前球面空间数据结构的基础上，讨论了利用Snyder等积投影在二十面体上建立球面空间基础剖分方式的思路，然后在初始投影面上采用六边形格网进行层次细分，获得多分辨率的全球铺盖。提出了基于六边形格网的三叶节点管理与瓦片编码的基本思路，确立了球面不同实体的六边形格网表达模式。在此基础上，提出了基于球面六边形铺盖的Voronoi图生成算法，实验验证了算法的正确性与效率。