2016年新疆呼图壁6.2级地震前b值异常特征研究

利用2009年以来中国地震台网中心地震编目资料,以2016年新疆呼图壁6.2级地震作为研究对象,采用最大似然法进行b值空间扫描计算,获取震前震中及其邻区地震b值的空间图像。研究结果显示,2016年呼图壁6.2级地震发生在震前显著低b值区域,该异常特征可能反映了地震孕育的应力积累过程,印证了b值的物理意义。     

Non-stationary spatial covariance structure estimation in oversampled domains by cluster differences scaling with spatial constraints

In the analysis of spatiotemporal processes underlying environmental studies, the estimation of the non-stationary spatial covariance structure is a well known issue in which multidimensional scaling (MDS) provides an important methodological approach (Sampson and Guttorp in J Am Stat Assoc 87:108–119, 1992). It is also well known that approximating dispersion by a non-metric MDS procedure offers, in general, low precision when accurate differences in spatial dispersion are needed for interpolation purposes, specially if a low dimensional configuration is employed besides a high number of stations in oversampled domains. This paper presents a modification, consisting of including geographical spatial constraints, of Heiser and Groenen’s (Psychometrika 62:63–83, 1997) cluster differences scaling algorithm by which not the original stations but the cluster centres can be represented, while the stations and clusters retain their spatial relationships. A decomposition of the sum of squared dissimilarities into contributions from several sources of variation can be employed for an exploratory diagnosis of the model. Real data are analyzed and differences between several cluster-MDS strategies are discussed.     

古登堡-里希特定律中的b值统计样本量研究

b值是研究地震活动的重要指标,其广泛应用于地震危险性分析和地震预测研究之中,与实际资料的完整性、样本量的大小、计算方法等因素有着重要的关系。常见的b值计算方法有最小二乘法和最大似然法,样本量的大小对这2种方法影响很大。本文利用蒙特卡罗模拟地震目录和汾渭地震带实际目录作为样本,从中抽取不同大小的样本量进行计算,研究不同样本量下这2种方法计算得到的b值与设定值或真实值之间的差别。结果表明,最小二乘法需要的最低样本量为1000,最大似然法为200;当样本量达不到要求时,计算出的b值是不可靠的;由于对样本量的要求不同,前者适用于计算区域的整体b值,而后者在研究某区域b值在时间轴上的变化方面更有优势。本研究为确定2种b值计算方法对样本量的最低要求提供了参考依据。     

A latent class MDS model with spatial constraints for non-stationary spatial covariance estimation

Multidimensional scaling (MDS) has played an important role in non-stationary spatial covariance structure estimation and in analyzing the spatiotemporal processes underlying environmental studies. A combined cluster-MDS model, including geographical spatial constraints, has been previously proposed by the authors to address the estimation problem in oversampled domains in a least squares framework. In this paper is formulated a general latent class model with spatial constraints that, in a maximum likelihood framework, allows to partition the sample stations into classes and simultaneously to represent the cluster centers in a low-dimensional space, while the stations and clusters retain their spatial relationships. A model selection strategy is proposed to determine the number of latent classes and the dimensionality of the problem. Real and artificial data sets are analyzed to test the performance of the model.     

低等级河流CO2分压的时空变化及驱动因素——以汉江流域月河为例

河流CO₂排放是全球碳循环的重要组成部分。 以汉江上游流域低等级(Strahler 等级 1 ～ 3) 河流月河为研究对象,采样测定 2016 年 12 月和 2017 年 6 月的关键环境因子并计算河流 CO₂分压(pCO₂)。 利用统计学模型,探讨不同等级河流水环境因子的时空变化及关键控制因素。 结果表明,月河流域低等级河流 CO₂约有 87% 的采样点过饱和,pCO₂变化范围是 135～5960 μatm,不同等级河流环境因子和pCO₂具有明显的时空差异,且河流pCO₂随着河流等级的增加而增加。利用 R 语言“ggpair”函数分析显示,河流pCO₂与建设用地占比、耕地占比和总氮(TN)、总磷(TP)、溶解性有机碳(DOC)浓度呈正相关,与森林用地占比、溶解氧(DO)浓度及坡度呈负相关。 对比分析不同等级河流的关键控制因素发现,低等级河流 pCO₂受土地利用和环境因子共同控制,且土地利...     

2013年芦山MS7.0地震震源区背景噪声源特征分析

应用背景噪声互相关信息研究强震前后地下介质波速变化时,噪声源的方位性特征会影响互相关函数形态,从而对波速变化有效估计造成影响。本文使用2013年芦山M_S7.0地震震源区附近的天全台(TQU)2013年全年的连续波形记录,计算其垂直分量的噪声功率谱概率密度函数,分析背景噪声源能量强度特征;并通过频域极化法计算噪声源极化率以及极化方位角的概率密度函数,研究噪声源的极性特征。结果表明,研究区小于0.05Hz的长周期噪声源种类较多,且具有噪声能量强度和极化程度较高、极化方位性明显的特点;第一类地脉动(0.05～0.1Hz)极化方位角为30°和210°,噪声能量较低;第二类地脉动(0.1～0.5Hz)极化方位角分布在150°～210°,噪声能量较高,且其能量强度具有季节性变化特征;大于1Hz的高频噪声主要来自人类活动,噪声能量水平受人类活动强弱影响明显。因此,即使在远离海洋的大陆地区,在利用背景噪声监测局部波速变化时,应注意噪声强度以及噪声源方向性变化的影响。     

多窗谱分析在Q值估算中的应用

正弦窗谱分析和Slepian窗谱分析是两种常用的多窗谱分析方法.本文利用两种窗函数分别对含噪声的衰减模型进行谱分析对比,并根据谱比法估算了Q值.研究结果表明：正弦窗函数谱分析应用的效果优于Slepian窗谱分析应用的效果,而且多正弦窗谱估计更接近真实的谱.对于深部地层,噪声的影响更加严重,利用多正弦窗谱估计估算的Q值更接近理论的Q值.     

2020年河北唐山5.1级地震前震源参数变化

利用谱分析方法对河北省测震台网2016年1月—2020年7月唐山老震区(117.5°～119.5°E,39°～41°N)85次M_L≥2.5地震进行震源参数分析,发现该时段唐山老震区应力降范围在0.1～10.3MPa,主要集中在0.1～1.0MPa,其中应力降小于2MPa的地震占81%。当2.5≤M_L≤3.5时,应力降、拐角频率与震级之间无明显的对应关系;ML≥4.0地震较少,但应力降有随震级增大而增大的趋势,拐角频率有随震级增大而减小的趋势。2019年12月5日河北丰南M4.5地震和2020年7月12日唐山M5.1地震之间发生了 7次M_L≥2.5地震,震级范围为2.5≤M_L≤2.8,提取该震级范围的震源参数进行时空分析,发现唐山M5.1地震前有2次明显的高应力降事件,2次高应力降事件呈现出应力降数值高、拐角频率高、震源尺度小的特点,表明单位体积所释放能量较多。2次高应力降事件均发生在唐山M5.1地震震中17km范围内,可能是唐山M5.1地震前震源区构造应力较高的一个标志。     

Attenuation in the uppermost inner core from PKP recordings at African seismological stations

The attenuation factor Q_P at the top of the inner core is evaluated by using the amplitude spectral ratio of PKPdf and PKPbc phases observed at African stations (BGCA mostly), from strong deep earthquakes in the Pacific Ocean area. The maximum depth of penetration of the PKPdf phase into the inner core (IC) is roughly 377 km, and the sampled region of IC is centered beneath the Southern Indian Ocean. The derived mean value of Q_P is 249 ± 31 (95% confidence level) in the frequency range 0.2–2 Hz, where no frequency dependence of attenuation has been reliably observed. By using Student’s t-test, we show that the value is statistically significantly different (with a probability greater than 95%) from other mean values of Q derived by using the same method, for both the western (180 °W to 40 °E) and eastern (40 °E to 180 °E) hemispheres of the IC. The decrease of Q with the radius of the turning point (denoted by r^TP), according to Q_P = 840 − 0.62 r^TP, has a moderate statistical support (the R-squared value is 38%). A slightly increase of Q as a function of the angle of the PKPdf path within the inner core with respect to the Earth’s spin axis is observed, in agreement with various investigations performed in the time domain. However, the value of the anisotropy, if any, is suggested to be around 3%.     

鄱阳湖湿地中低滩典型植物群落的生物多样性及影响因子

周期性水文节律是影响洪泛湖泊洲滩湿地植物群落物种组成与生物多样性的重要驱动力。本研究以鄱阳湖中低滩典型植物群落为研究对象,通过实地样方调查与统计方法分析植物群落的生物多样性格局及其关键环境因子。结果表明：鄱阳湖中低滩代表性群落分别是灰化薹草群落和虉草群落;植物群落的Shannon-Wiener多样性指数均值为1.5,Pielou均匀度指数均值为0.55,生物多样性与物种均匀度偏低。虉草群落的均匀度、多样性指数高于灰化薹草群落,但二者物种丰富度差异不明显。土壤铵态氮、总磷及土壤含水量和高程是影响植物群落结构与生物多样性的关键因子,其中灰化薹草的物种多样性与土壤铵态氮高度相关,而虉草的均匀度则与土壤总磷关系更密切。此外,鄱阳湖中低滩环境下,灰化薹草群落的均匀度随土壤总磷含量的升高呈现U型响应曲线,虉草则是倒U型,这表明,鄱阳湖中低滩环境下,灰化薹草群落和虉草群落生物多样性对单个、同一的环境因子存在不同的适应机制。     

Microfracture processes in the breakdown zone during dynamic shear rupture inferred from laboratory observation of near-fault high-frequency strong motion

High-frequency velocities are measured during stick-slip motion in the immediate vicinity of a fault in a granite sample to reveal the microscopic process taking place in the breakdown zone defined in the slip-weakening model. It is found that 1) the onset time of the observed strong motion approximately coincides with the local rupture onset time, 2) the observed near-fault high-frequency strong-motion duration is approximately proportional to the local breakdown time, and 3) the power spectra of strong motions exhibit significant amplitudes at frequencies above the value off _max, wheref _max is a cut-off frequency relevant to rupturing the breakdown zone. These observations suggest that the high-frequency motion would be due to the incoherent brittle microfracture whose characteristic scale is much shorter than the breakdown zone size. We present a stochastic fault model to synthesize the near-fault high-frequency velocity waveforms. In the model, a number of small circular subfaults are distributed randomly on the fault and the rupture onset time of an individual subfault is assumed to be random. The main features of the observed velocity waveforms are well explained by this numerical modeling. It is concluded that approximately half of the total energy of high-frequency elastic waves observed at a point is radiated from the propagating breakdown zone. We emphasize the importance of the observation of near-fault high-frequency strong motions for large shallow earthquakes.     

Distribution of<Emphasis Type="Italic">L</Emphasis><Subscript>g</Subscript> coda<Emphasis Type="Italic">Q</Emphasis> in the Chinese continent and its adjacent regions

785 traces of vertical components from shallow earthquakes recorded by 10 CDSN (Chinese Digital Seismographic Network) stations and 5 GSN (Global Seismographic Network) stations were collected to study the attenuation characteristics ofL _g coda in the Chinese continent and its adjacent regions. The records were processed first using the stack spectral ratio method to obtain the average values ofQ ₀ (Q at 1Hz) and η, the frequency dependence, ofL _g coda in the ellipses corresponding to the paths. The back-projection technique was then employed to obtain the tomographic maps ofQ ₀ and η values, and the distribution of their errors. Results indicate that in the studied areaQ ₀ varies between 200 and 500. The lowest value ofQ ₀ exists in the Yun-nan-Tibetan region, while the highest value ofQ ₀ occurs in the southern edge of Siberian platform. η varies between 0.3 and 0.8. For most part of the studied area η varies inversely withQ ₀.     

云南测震台网台站场地响应与ML震级测定的讨论

利用2016年云南测震台网记录到的地脉动数据,运用H/V谱比法计算分析了47个测震台站在0.1～20.0Hz频段内的场地响应。选取2012～2016年期间云南测震台网记录到的ML≥2.5地震做单台震级偏差统计分析,挑出受场地放大作用而出现单台震级大于台网平均震级的台站做去场地放大校正,然后重新统计单台震级偏差情况。计算结果显示云南测震台网的台站受台基条件和所处位置等地质构造因素影响,均存在一定程度的场地放大作用,大部分台站场地响应的卓越频率为1～6Hz,放大倍数为2～4倍。受场地放大作用的影响,大姚、芒市等19个台站的单台ML震级大于台网平均震级。在去除场地放大作用后,台站单台震级与台网平均震级的偏差有所减小。     

Density control in Potamogeton perfoliatus L. and Potamogeton pectinatus L.

The effect of density on the growth, recruitment of new ramets, biomass allocation, rhizome spacer length and rhizome branching of the submersed macrophyte Potamogeton perfoliatus L. was experimentally evaluated in a mesocosm with three different initial shoot densities. The findings suggest that the number of primary shoots available in the beginning of the season can strongly influence patterns of growth and clonal reproduction. In contrast to many studies that found decreasing production parameters with plant density, ramet and biomass production of Potamogeton perfoliatus plants were highest at medium plant density. This is probably due to negative feed-back through crowding at high density and unclear negative effects at low density. Shoot allocation tended to increase with density, rhizome allocation tended to decrease with density and root biomass remained unchanged. At low density Potamogeton perfoliatus produced longer rhizome spacers and more branchings than at higher densities. Shorter rhizome spacers at high plant density probably restrict patch expansion and cause discrete patch shapes. A likely mechanism for plastic changes in clonal architecture is increasing competition for light at increasing density, but other density-dependent factors may also contribute.Investigations on propagule numbers of tubers and turions show that self-regulation of ramet number was associated with self-regulation of propagule number in both Potamogeton perfoliatus and Potamogeton pectinatus, with higher densities producing less propagules per plant.     

Calculation of b value and its application in earthquake prediction

The improved calculation method ofb value is presented in this paper. The method can enlarge the role of earthquake occurrence frequency inb value calculation and thus increase theb value variation amplitude. In this case, the combination structure variation between earthquake magnitudes and corresponding frequencies could be shown clearly. According to the calculation and analysis for limited mainshocks in the complete seismicity data of selected monitored area with assigned consistent lowest magnitude, the precursor anomaly features, quantitative indexes and the calculation formula of relative subject function ofb value variation have been preliminarily worked out. The prediction in short period (from 1 to 3 months) for damage earthquakes in the monitored area mentioned above can be put forward on the basis of the results of quantitative calculation and analysis.     

2017年6月3日内蒙古阿拉善左旗5.0级地震强震记录及特征分析

2017年6月3日内蒙古阿拉善左旗发生5.0级地震,位于甘肃天祝-古浪一带的"西部烈度衰减台阵"得到充分触发,甘肃强震动台网的50台强震仪获得了主震加速度记录。本文首先对150条强震动记录进行常规处理,计算出近场强震动记录的加速度峰值随震中距的分布情况;根据4个典型台站的加速度时程记录及其加速度反应谱,分析本次地震的基本特征;然后将实际观测数据与意大利新一代地震动衰减公式对比,分析峰值加速度（PGA）及谱加速度衰减关系;最后结合已有的工程场地地质资料,采用H/V谱比法对4个不同类别的典型台站进行分析,发现该方法能很好地反映实际台站场地的反应特征。     

2017年8月8日四川九寨沟7.0级地震强震记录及特征分析

2017年8月8日四川九寨沟县发生7.0级地震,中国数字强震动台网布设在四川、甘肃、陕西、宁夏的66个强震台获得主震加速度记录。本文首先对198条三分向强震记录进行常规处理,计算出近场强震记录的加速度峰值随震中距的分布情况;再根据2个典型台站的加速度时程记录,通过计算其加速度反应谱并与设计反应谱比较,分析本次地震的基本特征;然后将实际观测数据与意大利新一代地震动衰减公式对比,分析峰值加速度（PGA）及谱加速度的衰减关系;最后结合已有的工程场地钻探资料,采用H/V谱比法对2个不同类别的典型台站进行地场地效应分析,发现该方法能很好地反映实际台站场地的反应特征。     

Nanociliates of the order Prostomatida: Their relevance in the microbial food web of a mesotrophic lake

Two nanociliates of the order Prostomatida,Pseudobalanion planctonicum (12–18 µm) andUrotricha furcata (12–21 µm), were found to be the most abundant ciliates in the epilimnion of Piburger See, a small mesotrophic lake. Temperature and food availability were the main factors controlling the sudden increase in abundance, which reached a maximum of 101 cell ml^–1 at the beginning of summer. During their exponential development in numbers and biomass, a strong decrease in chlorophylla and in the abundance of phytoplankton, especiallyRhodomonas, was observed. We assume, therefore, thatPseudobalanion planctonicum andUrotricha furcata together with rotifers, mainlyPolyarthra dolichoptera, are able to reduce the phytoplankton biomass in the upper epilimnion to the same level as found during the clearwater phase. Preliminary results of grazing on bacteria suggest that these nanociliates are omnivorous, although their impact on bacterial assemblages was low (3.1% of the standing stock grazed per day). Feeding on the base of the food web combined with their high abudance at certain times makes them an important link for higher trophic levels. This study constitutes the second report onPseudobalanion as an important component of the microbial food web in lakes.