Selection of ground motion time series and limits on scaling

A procedure to select time series for use in non-linear analyses that are intended to result in an average response of the non-linear system is proposed that is not based simply on magnitude, distance, and spectral shape. A simple model of a yielding system is used as a proxy for the non-linear behavior of a more complicated yielding system. As an example, Newmark displacements are used as a proxy for more complex slope-stability models. The candidate scaled time series are evaluated to find those that yield a response of the simple non-linear system that is near the expected response for the design event. Those scaled time series with responses near the expected value are selected as the optimum time series for defining average response even if the scale factors are larger than commonly accepted (e.g. scale factors >factor of 2).     

Mechanisms and Model Diversity of Trade-Wind Shallow Cumulus Cloud Feedbacks: A Review

Shallow cumulus clouds in the trade-wind regions are at the heart of the long standing uncertainty in climate sensitivity estimates. In current climate models, cloud feedbacks are strongly influenced by cloud-base cloud amount in the trades. Therefore, understanding the key factors controlling cloudiness near cloud-base in shallow convective regimes has emerged as an important topic of investigation. We review physical understanding of these key controlling factors and discuss the value of the different approaches that have been developed so far, based on global and high-resolution model experimentations and process-oriented analyses across a range of models and for observations. The trade-wind cloud feedbacks appear to depend on two important aspects: (1) how cloudiness near cloud-base is controlled by the local interplay between turbulent, convective and radiative processes; (2) how these processes interact with their surrounding environment and are influenced by mesoscale organization. Our synthesis of studies that have explored these aspects suggests that the large diversity of model responses is related to fundamental differences in how the processes controlling trade cumulus operate in models, notably, whether they are parameterized or resolved. In models with parameterized convection, cloudiness near cloud-base is very sensitive to the vigor of convective mixing in response to changes in environmental conditions. This is in contrast with results from high-resolution models, which suggest that cloudiness near cloud-base is nearly invariant with warming and independent of large-scale environmental changes. Uncertainties are difficult to narrow using current observations, as the trade cumulus variability and its relation to large-scale environmental factors strongly depend on the time and/or spatial scales at which the mechanisms are evaluated. New opportunities for testing physical understanding of the factors controlling shallow cumulus cloud responses using observations and high-resolution modeling on large domains are discussed.     

中国东西重力潮汐剖面

为了检验体潮与海潮的理论模型,分析了中国东西重力潮汐剖面（1981年9月-1985年1月）。同时,为研究LaCoste ET-20和ET-21重力仪的格值系统,建立了一条由17台LaCoste G型和2台LaCoste D型重力仪观测的重力垂直基线。在基线上标定的结果表明,ET-21重力仪的格值大了1％。由标定得到的格值计算剖面上各测站的潮汐因子,经海潮改正后,接近Wahr模型值,振幅因子的残差:O₁波小于0.3μGal,M₂波小于0.4μGal。但是上海和拉萨的观测经海潮改正后,相位迟后有很大的改善,振幅因子却更偏离于模型值,其潮汐异常主要是近海的海潮模型不完善,以及在海潮计算中,所采用的地球模型未考虑地壳与上地幔的横向不均匀性所引起。     

Near‐field seismic effects in a homogeneous medium and their removal in vertical seismic profile attenuation estimates

To better understand (and correct for) the factors affecting the estimation of attenuation (Q), we simulate subsurface wave propagation with the Weyl/Sommerfeld integral. The complete spherical wavefield emanating from a P‐wave point source surrounded by a homogeneous, isotropic and attenuative medium is thus computed. In a resulting synthetic vertical seismic profile, we observe near‐field and far‐field responses and a 90° phase rotation between them. Depth dependence of the magnitude spectra in these two depth regions is distinctly different. The logarithm of the magnitude spectra shows a linear dependence on frequency in the far‐field but not in those depth regions where the near‐field becomes significant. Near‐field effects are one possible explanation for large positive and even negative Q‐factors in the shallow section that may be estimated from real vertical seismic profile data when applying the spectral ratio method. We outline a near‐field compensation technique that can reduce errors in the resultant Q estimates.     

断层附近地面地震动空间分布

运用震源位错模型, 分析矩形垂直断层及倾斜断层走向滑动和倾向滑动的近场地震动场，以地表地震动的傅立叶振幅谱比为参量考察断层附近地震动空间分布的特点. 结果表明, 断层附近的地震动强度主要受近旁子断层的控制，高强度的地震动分布在紧靠断层两侧有限的带状区域内，长周期分量受断层破裂传播方向性的影响. 走向滑动的方向性影响主要表现在垂直于断层走向的分量，倾向滑动则表现在平行于断层走向的分量，且深震在地面上引起的地震动强度分布比浅震要平缓，影响范围宽. 倾斜断层产生的地震动有明显的上盘效应，空间分布不对称，与观测结果相符. 最后给出了断层附近近场地震动强度分布拟合函数的表达式，并与美国的1997统一建筑规范规定的近场因子作了比较.      

川滇强震前地震活动空间扫描短期特征

对比分析了川滇地区近30年强震活跃段地震活动因子A值和空间集中度C值的全时空扫描结果.结果表明,川滇地区大地震孕育进入短期阶段时,震中周围地区的中小地震活动在A值和C值出现不同程度的变化,而且选取地震活动因子A值可更好地表征川滇地区的地震活动在时、空、强方面短期的综合特征.     

大地震牵联的晚期最大近震和远震震级的计算公式

在我国大陆M_s=7.3以上的大地震所牵联的晚期最大近震和远震的应变能量依赖于如下诸因素:1、主震的应变能量;2、主震后当天最大近震的应变能量;3、主震后15天内最大近震的应变能量和发震时间.文中公式(9)和(10)则具体给出了定量的表示式.      

Evidence for solar forcing in variability of temperatures and pressures in Europe

Daily temperature and pressure series from 55 European meteorological stations covering the 20th century are analyzed. The overall temperature mean displays a sharp minimum near 1940 and a step-like jump near 1987. We evaluate the evolution of disturbances of these series using mean squared inter-annual variations and “lifetimes”. The decadal to secular evolutions of solar activity and temperature disturbances display similar signatures over the 20th century. Because of heterogeneity of the climate system response to solar forcing, regional and seasonal approaches are key to successful identification of these signatures. Most of the solar response is governed by the winter months, as best seen near the Atlantic Ocean. Intensities of disturbances vary by factors in excess of 2, underlining a role for the Sun as a significant forcing factor of European atmospheric variations. We speculate about the possible origin of these solar signatures. The last figure of the paper exemplifies its main results.     

Seismic isolation of cable‐stayed bridges for near‐field ground motions

This study examines the efficacy of using seismic isolation to favorably influence the seismic response of cable‐stayed bridges subjected to near‐field earthquake ground motions. In near‐field earthquake ground motions, large amplitude spectral accelerations can occur at long periods where many cable‐stayed bridges have significant structural response modes. This combination of factors can result in large tower accelerations and base shears. In this study, lead–rubber bearing seismic isolators were modeled for three cable‐stayed bridges, and three cases of isolation were examined for each bridge. The nine isolated bridge configurations, plus three non‐isolated configurations as references, were subjected to near‐field earthquake ground motions using three‐dimensional time‐history analyses. Introduction of a small amount of isolation is shown to be very beneficial in reducing seismic accelerations and forces while at the same time producing only a modest increase in the structural displacements. There is a low marginal benefit to continue to increase the amount of isolation by further lengthening the period of the structure because structural forces and accelerations reduce at a diminishing rate whereas structural displacements increase substantially. In virtually all cases the base shears in the isolated bridges were reduced by at least 50several instances by up to 80individual near‐field records showed large variability from one record to the next, with coefficients of variation about the mean as large as 50assessing the characteristics of near‐field ground motion for use in isolation design of cable‐stayed bridges. Copyright © 2003 John Wiley & Sons, Ltd.     

Spatio‐temporal distribution of near‐surface and root zone soil moisture at the catchment scale

Soil moisture is highly variable both spatially and temporally. It is widely recognized that improving the knowledge and understanding of soil moisture and the processes underpinning its spatial and temporal distribution is critical. This paper addresses the relationship between near‐surface and root zone soil moisture, the way in which they vary spatially and temporally, and the effect of sampling design for determining catchment scale soil moisture dynamics. In this study, catchment scale near‐surface (0–50 mm) and root zone (0–300 mm) soil moisture were monitored over a four‐week period. Measurements of near‐surface soil moisture were recorded at various resolutions, and near‐surface and root zone soil moisture data were also monitored continuously within a network of recording sensors. Catchment average near‐surface soil moisture derived from detailed spatial measurements and continuous observations at fixed points were found to be significantly correlated (r² = 0·96; P = 0·0063; n = 4). Root zone soil moisture was also found to be highly correlated with catchment average near‐surface, continuously monitored (r² = 0·81; P < 0·0001; n = 26) and with detailed spatial measurements of near‐surface soil moisture (r² = 0·84). The weaker relationship observed between near‐surface and root zone soil moisture is considered to be caused by the different responses to rainfall and the different factors controlling soil moisture for the soil depths of 0–50 mm and 0–300 mm. Aspect is considered to be the main factor influencing the spatial and temporal distribution of near‐surface soil moisture, while topography and soil type are considered important for root zone soil moisture. The ability of a limited number of monitoring stations to provide accurate estimates of catchment scale average soil moisture for both near‐surface and root zone is thus demonstrated, as opposed to high resolution spatial measurements. Similarly, the use of near‐surface soil moisture measurements to obtain a reliable estimate of deeper soil moisture levels at the small catchment scale was demonstrated. Copyright © 2007 John Wiley & Sons, Ltd.     

Near‐fault ground motions,and the response of elastic and inelastic single‐degree‐of‐freedom (SDOF) systems

In order to investigate the response of structures to near‐fault seismic excitations, the ground motion input should be properly characterized and parameterized in terms of simple, yet accurate and reliable, mathematical models whose input parameters have a clear physical interpretation and scale, to the extent possible, with earthquake magnitude. Such a mathematical model for the representation of the coherent (long‐period) ground motion components has been proposed by the authors in a previous study and is being exploited in this article for the investigation of the elastic and inelastic response of the single‐degree‐of‐freedom (SDOF) system to near‐fault seismic excitations. A parametric analysis of the dynamic response of the SDOF system as a function of the input parameters of the mathematical model is performed to gain insight regarding the near‐fault ground motion characteristics that significantly affect the elastic and inelastic structural performance. A parameter of the mathematical representation of near‐fault motions, referred to as ‘pulse duration’ (T_P), emerges as a key parameter of the problem under investigation. Specifically, T_P is employed to normalize the elastic and inelastic response spectra of actual near‐fault strong ground motion records. Such normalization makes feasible the specification of design spectra and reduction factors appropriate for near‐fault ground motions. The ‘pulse duration’ (T_P) is related to an important parameter of the rupture process referred to as ‘rise time’ (τ) which is controlled by the dimension of the sub‐events that compose the mainshock. Copyright © 2004 John Wiley & Sons, Ltd.     

A note on strength-reduction factors for design of structures near earthquake faults

Strength-reduction factors are analyzed for simplified near-fault, fault-normal and fault-parallel strong-motion displacements. It is shown that the common design rules for selection of the strength-reduction factors are conservative and properly describe the reduction amplitudes near faults of strong earthquakes, for fault-normal pulses. However, for fault-parallel displacements, the same reduction factors are not conservative and should be changed. It is recommended that for design close to active faults, the strength-reduction factors for all components of motion should be constant for all periods and equal to (2μ−1)^1/2, where μ is ductility.     

震前云下增温异常及其时段特征

利用卫星热红外图像资料做地震短临预报, 主要依据的是地表大气增温异常在卫星图像上的亮温反映。 但在阴云密布的天气条件下, 这种预报方法却受到了限制, 因为卫星无法探测到地面或水面是否有增温异常。 通过气象资料分析, 得知云层或其他气象条件引起的降温并不能改变震前地表温度增加的趋势。 某些地震之前虽然震中及其附近地区天空阴云密布, 地面增温幅度却可高达十几度。 云下增温曲线可划分为3个时段(即A、 B、 C段), 其中A段与C段分别为增温前与震后的温度变化曲线, 多与日照时间呈正相关关系, 特别是A段的这种关系更具普遍性。 然而, 反映震前地面增温特征的B段却与日照时间没有明显的相关性, 可见这种持续增温、 与云量无关的波状增温等都主要不是由日照或气象条件引起的, 而是一种与地下应力作用、 气体释放、 瞬变电场等有关的震兆现象。 因此, 提高对云下增温的系统观测能力, 是改善热红外地震预报的有效途径。     

长白山天池火山密码破译势在必行

长白山天池火山是中新世以来多次喷发并造成严重灾害的火山。通过十几年的火山地质及火山地震监测研究认为长白山天池火山近期不会马上喷发，但它是一座具有潜在喷发危险性的活动火山，并提出建立长白山火山观测站的重要意义，讨论了天地火山密码的破译需要调动各方面有利因素和有利条件。     

由调制模式讨论短临预报

在接近地震发生前,震源区和它的邻近地区处于不稳定状态。在这种情况下,一些微弱外因,如引潮力,大气压力或磁暴可以调制这些地区向发震发展的过程以及由这些过程所引起的前兆,在我们以前的文章中曾论述过这个问题。外因对前兆的调制效应可以分为以下几种类型: 1.过源调制这种调制是外因对应力积累单元(震中区)的不稳定过程的调制並相应引起前兆。2.过场调制过场调制是外因对震源外围调整区的不稳定性进行调制,並相应引起前兆。3.非震调制即外因对地壳内非地震的不稳定性进行调制,並相应引起某些观测项目的突变异常。例如某些蠕滑事件可以被外因调制,但不一定有地震发生。4.虚假调制这种调制是外因直接调制某种对象並引起假前兆。例如气候的突然变化引起动物异常等。值得指出的是,有时假前兆还可能与地震发生同步。这是因为外因一方面可以直接引起假前兆,另一方面对地震发生也有触发作用。在以前的文章中,我们介绍过许多我国的例子以证明调制模式。本文列举国外一些比较典型的震例以进一步证明调制模式对短临预报的普遍适用性。在国外的震例中,其中日本的震例有4个。它们是1978年元月14日伊豆半岛与大岛之间发生的7.0级地震。在这次地震前5天,距震中20公里的氡气观测站观测到了氡气的突然变化,此日为朔日;1980年6月29日伊豆半岛东方海中发生6.7级地震,在震前4天前前震突然频繁活动,此前震开始活动日接近望日;1976年7月26日日本伊势湾4.1级地震,该震虽不大,但地震前8小时在震中附近的伊良湖形变站记到临震当天的形变暴,此日为朔日。1977年11月6日,日本根府川3.9级地震,离震中10多公里的网代形变站在地震前6小时观测到形变暴,此日为望日。苏联的震例有二个,第一个例子是1978年11月2日,苏联中亚阿莱地方发生7级地震,震前两天安集延和塔什干地磁台磁场差值△F突然异常,此日为朔日。第二个例子是1972年2月7日加尔姆4.7级地震,这次地震前3—4天在离震中130公里的氡气站上观测到突然异常,此日为朔日。美国的一个震例是著名的感恩节地震,该震发生在1974年11月28日,震级为5.2。10月31日,即震前27天霍利斯特地磁台阵中有两个台的地磁场差值出现突变,此日恰好为望日。上述两台在震中西南10公里左右。由于固体潮资料是已知的,便于对比,所以文中对比的外因皆为固体潮。其它磁暴与大气压力变化调制的例子将在以后讨论。以上震例说明,在临近地震前震源以及外围地区已处于不稳定状态,因而此时外因能调制震源过程,激励震源变动,使之发生较大的前兆变化。因此突然的前兆变化与外因同步可视为地震即将来临的标志。此外文中还列举了美国加里福尼亚圣安德烈斯断层蠕滑加速与固体潮高潮同步的例子以及苏联中亚地镭区的突然变化与固体潮高潮同步的例子。因此应当指出,外因也可能引起非震滑动和假前兆。     

淮阴台井下测震震级偏差初探

依据台站两年来实测的地震震级和江苏省区域测震台网定的震级进行比较,计算出各个地震的偏差值和台站的震级校正值,并获得相应的标准误差,最后对影响震级差值因素进行了探讨。     

The Time-Frequency Energy Attenuation Factor and Its Application on the Basis of Gauss Linear Frequency-Modulated Continuous Wavelet Transform

Based on the Gauss linear frequency-modulated wavelet transform, a new characteristic index is presented, namely time-frequency energy attenuation factor which can reflect the difference features of waveform in earthquake focus mechanism, wave traveling path and its attenuation characteristics in focal area or near field. In order to test its validity, we select the natural earthquakes and explosion or collapse events whose focus mechanisms vary obviously, and some natural earthquakes located at the same site or in a very small area. The study indicates that the time-frequency energy attenuation factors of the natural earthquakes are obviously different with that of explosion or collapse events, and the change of the time-frequency energy attenuation factors is relatively stable for the earthquakes under the normal seismicity background. Using the above-mentioned method, it is expected to offer a useful criterion for strong earthquake prediction by continuous earthquake observation.     

地震台常用计算软件

概述了近震三要素计算、体波与面波震级计算,以及形变前兆数据校正批处理等程序设计依据和使用功能.     

Radiation Conditions near Exoplanets of the TRAPPIST-1 System

Geomagnetism and Aeronomy - Stellar and galactic cosmic rays (SCR and GCR) are the primary factors influencing the radiation conditions near exoplanets. The GCR spectrum and its time variations are...     

Scattering of seismic waves by cracks in multi-layered geological regions: I. Mechanical model

In this work, a hybrid boundary integral equation method (BIEM) is developed, based on both displacement and hypersingular traction formulations, for the analysis of time-harmonic seismic waves propagating through cracked, multi-layered geological regions with surface topography and under plane strain conditions. Specifically, the displacement-based BIEM is used for a multi-layered deposit with interface cracks, while the regularized, traction-based BIEM is used when internal cracks are present within the layers. The standard uni-dimensional boundary element with parabolic shape functions is employed for discretizing the free surface and the layer interfaces, while special discontinuous boundary elements are placed near the crack tips to model the asymptotic behaviour of both displacements and tractions. This formulation yields displacement amplitudes and phase angles on the free surface of a geological deposit, as well as stress intensity factors near the tips of the cracks. Finally, in the companion paper, numerical results are presented which show that both scattered wave and stress concentration fields are sensitive to the incidence seismic wave parameters and to specific site conditions such as surface topography, layering, the presence of cracks and crack interaction.