基于钻孔应变地震波记录确定地震面波应变震级

近年发展的高采样率的钻孔应变仪可以记录到地震波造成的水平应变,是动态库仑应力研究的重要手段.利用钻孔应变仪记录的应变地震波确定地震震级,是一个重要的科学课题.本文收集了我国10个应变台站四分量钻孔应变仪2020年1—3月记录的10 Hz采样应变地震波资料,共选出震级M≥4.0的浅源地震68个,用最小二乘法求得应变震级公式为Mε=lg E max+1.65 lg(Δ)+1.43.对于6.5级以下的地震,计算得到的应变震级ε与中国地震台网中心公布的震级M CENC基本一致:M CENC=1.03ε-0.23,但本研究中的两个7级地震,应变震级出现了震级饱和现象.本文的基本结论是:应变定震级是可行的,但对于两个7级地震的饱和现象需要进一步深入研究,因为它们不但涉及震级确定,而且涉及远震动态库仑应力触发地震的研究.今后要对更多的大震钻孔应变波形记录进行分析.     

四分量钻孔应变仪计算式梳理及震例应用

从四分量钻孔应变仪基本原理式的分析出发,可知首先得到的物理量是岩石面应变和切应变及主应变的方位角,然后得到的最大、最小主应变是间接结果,建议多使用面应变和切应变的表示方法。由此说明当下需要重视灵敏系数A、B的实用化研究。据此思路,以云南省昭通地区2012年彝良M 5.7地震和2014年鲁甸M 6.5地震为例,对2次震中附近几台四分量钻孔应变仪记录的观测数据进行计算,初步分析表明,基于面应变和切应变的视角进行分析,其效果多优于以元件为单位的分析,可直接得到面应变和切应变异常及特征;2个面应变测量数据间的相关系数曲线,有时会在震前数天和震时出现异常变化,此新线索值得关注。     

地壳应变场观测中体应变与面应变转换系数的计算

将钻孔体应变仪与分量式应变仪的观测资料在面应变平台上进行整合,对于解决目前两种应变仪观测数据的评估、分析、处理和地震预报问题有实际意义．根据潘立宙-陈沅俊和Evertson理论及弹性力学知识,分别建立了平面应力作用下体应变和面应变观测的力学模型,推导了观测钻孔、空孔和无孔岩石体应变与面应变转换系数的计算公式,发现它们都可以归结为同一公式描述,差异仅在于k（体应变仪钢筒内壁或无孔岩石面应变与空孔岩石面应变之比）的取值不同．用Evertson理论推导的公式与空孔岩石情形相近,当岩石弹性模量为4times;1010——8times;1010 Pa时,二者都可以看成是对潘-陈公式的一种简化、近似计算;无孔岩石的情况则相当于在岩石弹性模量为1times;1010 Pa时对该式的一种估计. 文中结合实际情况对转换系数的各种影响因素进行了详细分析．      

分量式钻孔应变观测耦合系数的计算

根据双衬套钻孔应变观测力学模型,推导出平面应力作用下各分量应变观测中两个耦合系数(A、B)的计算公式,为进一步确定地壳应变场最大、最小主应变的数值及方向提供了必需的前提条件,对当前国内外开展的利用钻孔应变进行地震、火山和板块边界的观测研究具有一定积极意义.研究结果表明,A、B与用双环模型和复变函数法解算出的c(面应变响应因子)、d(剪应变响应因子)之间分别存在2倍的关系(c=2A,d=2B),并且二者绘制的曲线完全一致,c、d的物理含义分别是地壳岩石面应变与剪应变观测的井孔耦合系数.     

武都四分量钻孔应变观测数据分析

通过对多年水位、应变观测数据分析发现,水位上升引起应变下降变化（压应力增加）,两者变化同步.在水位大幅度变化时段求取应变响应灵敏度系数K,由K值可以定量剔除水位变化对应变测值的干扰.利用两两正交的4道应变测值可以求取2组面应变值,曲线形态相似则说明4道元件测值可靠性高.武都钻孔应变2组面应变值变化趋势基本相同,总体呈现波动下降（压性）变化.由2007年、2008年应变测值计算差异值η,其绝对值的平均值为0.21,数值较小,说明武都应变仪工作稳定,所测数据基本可靠.     

2022年青海杂多Ms5.9地震震源机制中心解及位移场和应变场特征分析

通过建立目标函数和Levenber-Marquardt迭代等数学方法求出杂多地震的多个震源机制解的中心解，并用Wells和Coppersmith的统计公式估算出断层面大小和滑动量，进一步计算出主震所产生的同震位移场及应变场。结果表明：(1)推断节面II(走向342.12°,倾角70.62°,滑动角是-175.99°)是本次地震的主断层面。(2)在水平位移场方面，震中东北物质向震中涌入，西北、东南物质向外涌出；在垂直位移场方面，震中东北部为沉降，东南部为隆升。综合分析认为，水平位移大于垂直位移，判断此次地震为走滑型。(3)体应变在震中东北侧呈现压缩，在震中西北、东南两侧呈现伸张，北向应变、东向应变、北东向应变在震中均呈现八花瓣样式分布。(4)体应变形态与面应变分布大体相同，表现在面应变继承体应变。本研究可为地震对周围的影响，地震发生原因提供分析依据。     

基于应变模态的结构损伤定位方法

针对简支梁的单一位置及其多位置损伤，利用结构有限元分析软件计算得到简支梁的位移模态，再通过应变和位移之间具有一阶导数的关系，对简支梁进行了应变模态分析。结果表明，应变模态对损伤比较敏感而位移模态对损伤不够敏感；当损伤发生在应变模态的节点处时，损伤不易被识别，但是可以结合多阶应变模态进行损伤识别。最后对应变模态法的工程实用性进行了评价。     

反应位移法中弹簧系数求解方法改进研究

采用反应位移法进行地下结构抗震计算时,关键是确定土体的弹簧系数,弹簧系数的取值直接影响计算结果。在现有的静力有限元求解弹簧系数方法的基础上,通过不同的施力方式共设计了6种静力有限元求解弹簧弹簧系数的方法,并对这6种计算方法进行对比分析计算。结果表明,整体和整体同时求解径向和切向弹簧系数这两种方法的计算结果偏于危险;单独和单独同时求解水平和垂直向弹簧系数这两种方法的计算精度最好;整体和整体同时求解水平和垂直向弹簧系数这两种方法的计算结果偏于安全。     

钻孔体应变与面应变观测井孔耦合系数的计算

钻孔应变观测系统（岩石、 膨胀水泥和应变仪钢筒）存在显著的井孔耦合效应,只有确定这一耦合系数,才能得到地壳岩石的真实应变值,从而实现不同测点数据的可比性．本文根据双衬套理论及弹性力学理论,建立了三维空间应力作用下体应变与面应变观测力学模型,并进一步推导各自井孔耦合系数计算式,发现两组系数与井孔的受力状况密切相关,分别与不同力源引起的应变信号相对应．亦即应力比（钻孔轴向应力与平面应力之比）不同,耦合系数也不一样,体应变随应力比的增大而下降,面应变则上升. 本文结果还表明平面应力作用下的耦合系数与外加应力无关,只与观测系统本身有关,故数值保持恒定. 此外,文中对其影响因素也进行了分析,结果表明,体应变和面应变的井孔耦合系数均随岩石弹性模量和泊松系数的增大而增大,且前者的幅度较大,井孔耦合材料水泥对二者影响均很小．      

滦县台YRY—2型钻孔应变仪两井孔固体潮观测的对比分析

本文介绍河北省滦县地震台两台YRY-2型钻孔应变仪的固体潮观测试验情况。对两口井的观测资料在数据处理过程中进行了多次调和分析计算。对不同方向的线应变及差应变观测资料进行了综合对比分析,结果表明:1.应变观测资料中含有较强的长趋势低频噪声和高频噪声,并且受气压的干扰明显。2.线应变受气压干扰比差应变高得多。3.两个井在各方向显示的主要潮汐波成份一致,为O_1、S_1,K_1、N_2、M_2、S_2波。4.经各种排除干扰方法的处理后,可得到较清晰的应变固体潮曲线和较为可信的应变固体潮调和分析结果。5.用一号井线应变计算出的差应变与二号井直接测到的差应变,两者的调和分析结果一致,两口井的固体潮观测起到了相互验证的作用。     

SCIENCE CHINA Earth Sciences SUBJECT INDEX TO VOLUME 57(2014)

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A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Distribution of throughfall and stemflow in multi‐strata agroforestry,perennial monoculture,fallow and primary forest in central Amazonia,Brazil

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd.     

Anthropogenic Eutrophication and Red Tide Outbreak in Lacustrine Systems of the Kashmir Himalaya

Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate.