地表潜在断错位移的概率评价方法

目前跨活动断层的线状工程的抗断设防一般是以断层位错确定性评价为基础 ,考虑的是最大位错量 ,与抗御灾害的风险设计的实际要求不相符。本文将走滑断层上最大位错点的位置分布及最大位错点两侧的位错展布 ,与可产生地表断错位移的强震复发模型联合 ,构造出评估走滑活动断层各部位地表潜在断错位移的概率性评价方法。最后 ,以鲜水河走滑断裂中带西北部的松林口 -乾宁段为例 ,对其未来 10 0年潜在断错位移的危险性做出定量评估 ,可给出断层段上各点不同超越概率水平下的潜在位移。这一研究结果 ,可为跨断裂的线形工程进行抗御地表潜在断错位移的风险设计提供科学依据.     

Seismic source identification and characterisation for probabilistic seismic hazard analyses conducted in the Buller–NW Nelson Region, South Island, New Zealand

A seismic source model is presented for use in probabilistic seismic hazard analyses to be conducted for sites within the Buller–NW Nelson region of New Zealand. The application of common probabilistic seismic hazard analysis (PSHA) methodology for sites in this region has been complicated by the long-held suspicion that the observed rates of seismic activity are high and not representative of long-term earthquake activity. However, recent analyses of geological, seismicity and geodetic data indicate that the extent of this anomaly may have been overestimated and that current rates of seismic activity within this region are likely to continue into the foreseeable future. Probable bounds for the most appropriate long-term rates of seismic activity are estimated after considering all available sources of constraint. These include geodetic analyses, plate-motion modelling, finite element modelling, structural geological considerations, paleoseismic information, tree-ring analyses, precarious rock information, observed seismicity and fundamental mechanics. A suite of fault sources is identified, and the observed seismicity is partitioned between these sources and a background source using Bayesian inference, and then analysed to obtain a magnitude–frequency distribution for each seismic source. The annual moment release rate for the region, resulting from the identified and characterised sources, is shown to be consistent with available constraints. Consequently, it is demonstrated that the observed seismicity in the Buller–NW Nelson region can be used to model future earthquake occurrence within the region and that standard PSHA may therefore be implemented within the region.     

A laboratory study of the effect of magnetite on NMR relaxation rates

We conducted a laboratory study to measure the effect of magnetite concentration and grain size on proton nuclear magnetic resonance (NMR) relaxation rates of sand mixtures and to determine the dominant mechanism by which relaxation occurs. We measured mixtures of quartz and three different forms of magnetite: a powdered synthetic magnetite; a small-grained, natural magnetite; and a large-grained, natural magnetite. The powdered synthetic magnetite was mixed with quartz in five concentrations ranging from 0.14 to 1.4% magnetite by weight; both sizes of natural magnetite were mixed with quartz in concentrations of 1 and 2% magnetite by weight. The NMR response of the water-saturated samples was measured and used to calculate four averaged relaxation rates for each magnetite concentration: the total mean log, bulk fluid, surface, and diffusion relaxation rates. The results of this study show that: 1) surface relaxation was the dominant relaxation mechanism for all samples except the powdered synthetic magnetite sample containing 1.4% magnetite; 2) the surface relaxivity is a function of the fraction of the surface area in the sample composed of magnetite; 3) there is no clear dependence of the diffusion relaxation rate on the concentration of magnetite.     

Developing probabilistic eruption forecasts for dormant volcanoes: a case study from Mt Taranaki,New Zealand

The majority of continental arc volcanoes go through decades or centuries of inactivity, thus, communities become inured to their threat. Here we demonstrate a method to quantify hazard from sporadically active volcanoes and to develop probabilistic eruption forecasts. We compiled an eruption-event record for the last c. 9,500 years at Mt Taranaki, New Zealand through detailed radiocarbon dating of recent deposits and a sediment core from a nearby lake. This is the highest-precision record ever collected from the volcano, but it still probably underestimates the frequency of eruptions, which will only be better approximated by adding data from more sediment core sites in different tephra-dispersal directions. A mixture of Weibull distributions provided the best fit to the inter-event period data for the 123 events. Depending on which date is accepted for the last event, the mixture-of-Weibulls model probability is at least 0.37–0.48 for a new eruption from Mt Taranaki in the next 50 years. A polymodal distribution of inter-event periods indicates that a range of nested processes control eruption recurrence at this type of arc volcano. These could possibly be related by further statistical analysis to intrinsic factors such as step-wise processes of magma rise, assembly and storage.     

汶川地震震后余滑和震后粘弹性松弛数值模拟分析

采用2010～2015年汶川地区GNSS震后形变资料,利用有限元法建立三维震后粘弹性松弛模型,通过二维格网搜索获得龙门山断裂带上盘最佳弹性层厚度和中下地壳最佳粘滞系数,并分析汶川地震震后2～7 a粘弹性松弛影响下的震后形变特征;然后采用2008～2009年GNSS震后形变资料,根据最佳参数建立粘弹性松弛与余滑组合模型,...     

利用同震和震后位移数据联合反演2011年日本MW9.0地震同震断层滑动

基于黏弹性球体位错理论,联合陆地和海底同震GPS数据以及日本本岛330个陆地GPS站点5～10年的震后数据,反演了日本Mw9.0地震的断层滑动模型,提升了断层滑动分布在细节上的合理性.首先,基于日本本岛330个陆地GPS站点震前2年和震后10年的连续观测数据,获取了日本Mw9.0地震震后5～10年的年平均位移,该时段的...     

一种四维同化方法的试验研究

文章利用一个有限区模式对一种资料四维同化过程作了试验研究，以考察四维资料同化对模式的预报过程的作用。试验结果表明:四维资料同化可以为模式提供一组四维动力协调的积分初值。对由于资料或模式原因造成的积分开始时的高频振荡有很好的抑制作用，使模式的积分稳定性增强。      

运用古地震数据评价东昆仑断裂带东段未来百年的强震危险性

通过收集、整理和分析青藏高原东北部22条断裂带上古地震定量数据,拟定了该区的地震复发概率密度函数.根据此函数对区内东昆仑断裂带东段不同段落上未来100年内强震原地复发的条件概率进行了初步研究.结果表明,该断裂带上自西向东的3个破裂段中,玛沁段和塔藏段未来20、50、100年的复发概率值介于0.76%~7.36%之间,玛曲段未来20、50年的复发概率值介于2.0%~5.26%,属于低概率事件;玛曲段未来100年的复发概率值为10.82%,属于中概率事件;整个段未来100年内至少发生一次7级以上强震的联合概率可达21.87%,属于中概率事件.考虑到概率模型的不确定性,进一步对各段进行了危险性的定性分类,综合评价认为玛沁段在未来百年内发生大震的危险性较低,玛曲段和塔藏段未来百年发生大震的危险性较高.最后将本文拟合的概率密度函数与传统通用函数计算的条件概率值进行比较,发现通用的复发概率函数随着自变量t/R的增大,因变量P的反映不如本文拟合函数的敏感.     

Probabilistic stability analyses of slopes using the ANN-based response surface

Slope stability analysis is a geotechnical engineering problem characterized by many sources of uncertainty. Some of these sources are connected to the uncertainties of soil properties involved in the analysis. In this paper, a numerical procedure for integrating a commercial finite difference method into a probabilistic analysis of slope stability is presented. Given that the limit state function cannot be expressed in an explicit form, an artificial neural network (ANN)-based response surface is adopted to approximate the limit state function, thereby reducing the number of stability analysis calculations. A trained ANN model is used to calculate the probability of failure through the first- and second-order reliability methods and a Monte Carlo simulation technique. Probabilistic stability assessments for a hypothetical two-layer slope as well as for the Cannon Dam in Missouri, USA are performed to verify the application potential of the proposed method.     

储层流体及其在岩石孔隙中的核磁共振弛豫温度特性

温度是影响核磁共振弛豫的一个因素。目前国内各实验室所做的核磁共振实验测量大都局限在室温下,实验温度与地下储集层温度有很大差别,因此有必要研究温度对流体及饱和流体岩石的核磁共振弛豫的影响,提高核磁共振测井资料评价精度。本文选取自由水、不同粘度脱气原油、饱和水以及饱和变压器油的储层贝瑞砂岩和储层碳酸盐岩样品进行核磁共振变温实验,测量温度从25℃变化到90℃。结果表明:自由水和原油的核磁共振横向弛豫时间(T2)都随温度的升高而增大。温度对饱和水贝瑞砂岩和碳酸盐岩核磁共振弛豫的影响不同,饱和水贝瑞砂岩核磁共振横向弛豫时间随温度升高而减小,而饱和水碳酸盐岩横向弛豫时间随温度升高而增大。无论是饱和油的贝瑞砂岩或是饱和油的碳酸盐岩,其核磁共振横向弛豫时间都随温度升高而增大。温度对核磁共振弛豫的影响,会造成室温下得到的横向弛豫时间截止值(T2cutoff)与储层温度下的实际值有偏差,影响储层束缚水饱和度和渗透率的计算结果,建议在核磁共振测井资料解释及应用时应考虑温度的影响。