顾及有效角动量与IGS超快解数据的极移预报方法

极移高精度预报对卫星实时定轨、深空探测器导航等应用至关重要.本文提出了一种联合有效角动量(Effective Angular Momentum, EAM)与国际全球卫星导航系统服务组织(International GNSS Service, IGS)提供的超快解数据进行极移预报的方法.该方法基于IGS超快解数据得到的极移第1天预报值, 对引入EAM得到的极移预报结果进行校正, 获得联合预报值.首先, 基于LS(Least Squares)+AR(Auto-Regressive)模型实现了引入EAM的极移预报, 相对国际地球自转与参考系统服务组织(International Earth Rotation and Reference Systems Service, IERS)提供的公报A数据, 在超短期(第1~10天)预报跨度可以得到更高精度的极移预报结果, 其中大气和海洋角动量发挥了主要作用.其次, 鉴于IGS超快解数据精度高、更新快的特点, 以IGS超快解为基础数据, 基于LS+AR模型可以得到极移第1天预报值, 其精度显著优于IERS公报A的极移第1天预报值.最后, 利用第1天预报值对顾及有效角动量的预报结果进行校正获得了联合预报值, 进一步提高了超短期极移预报精度(尤其是第1~5天).2020年7月24日—2022年1月30日间的联合预报结果表明: 第1~20天的预报值总体优于IERS公报A的预报值.其中, 第1~10天的预报精度显著提升, 在预报第1天, X、Y方向预报值相对公报A预报值的精度提升分别可达39.5%~62.3%和24.5%~51.9%;在预报第10天, 相对公报A预报值的精度提升分别可达28.0%~28.9%和21.9%~23.4%.

     

台湾费丛峡谷对强地面运动的影响研究──利用单台资料及2．5维SH混合方法

本文通过格林函数反褶积方法,由台湾峡谷附近的记录资料预测峡谷区的强地面运动的时程曲线．峡谷区的理论格林函数应用２．５维ＳＨ混合方法求解．通过格林函数反褶积方法得到的峡谷区费丛１及费丛２台的位移、速度、加速度和实际资料对比,取得了满意结果．计算结果表明,峡谷底部的峰值加速度相对峡谷边缘为最小;在靠近震中的一侧,峡谷的加速度的最大振幅相对比另一侧大．还给出了其余３个台的预测结果,研究了它们的加速度傅里叶谱和反应谱．     

大跨度桥梁强震动数字监测系统的研制

主跨1 196 m的龙江特大桥是我国第一座位于高烈度地震区的大跨度悬索桥,频繁的地震活动对大桥结构安全构成严重威胁。大桥建设时建立了健康监测系统,其中包含多个结构地震反应观测点,随后布设了场地强震动观测系统,这是对大桥地震响应观测的进一步补充和完善。本文详细介绍场地强震动观测系统的设计方案、系统构成、通信方式等。该系统获取的观测结果,可为龙江大桥在地震作用下结构健康诊断提供依据,为大桥结构地震响应分析提供可靠的地震动输入,有助于了解大桥结构在地震动作用下的反应特征, 提高大跨桥梁的抗震设计水平。     

Observations of vertical ground accelerations exceeding gravity during the 1997 Umbria-Marche (central Italy) earthquakes

We found extensive evidence that the vertical ground accelerations produced during the largest shock (M = 6.0) of the 1997 Umbria-Marche earthquake sequence exceeded 1g in two areas close to the heavily-damaged villages of Annifo and Colle Croce. This evidence comes from the striking observation of thousands of freshly fractured and broken rocks and stones in these areas. Some of the broken stones lie isolated on soft detritic soil while others had been previously piled up, probably a long time agoto clear the fields for farming. The freshness of the cuts and fractures and the consistency of the observations for thousands of rocks and stones in these areas indicate that these rocks were thrown upwards during the earthquake, with breakage occurring at the time of impact. Ground motion calculations consistent with the static deformation inferred from GPS and interferometry data, show that the broken stones and rocks are found in the zone where the strongest shaking took place during the earthquake and that most of the shaking there was vertical.     

GDS—1000宽频带通用流动数字地震观测系统

GDS-1000宽频带通用流动数字地震观测系统主要用于大陆岩石层的人工及天然地震台阵研究、强震观测以及余震观测台网的临时布设。其主要技术指标为:动态范围120dB,前放增益1,16,128倍可调,高端频率6.25,25,45Hz可调,采样率25,100,200Hz可调,1MB固态数据存储器借助地震数据的压缩软件可以存储3MB以上的数据,工作温度范围-10—45℃,功耗小于3W。定时接受的BPM无线电授时信号可保证记录系统时钟校正误差小于10ms。其智能化地震触发系统可处于下列模态:近震触发,远震触发,近震和远震触发,任意地面运动信号触发,以及手动触发和定时触发。DSR-1000数字地震数据回收系统用于GDS-1000的参数预置、地震事件数据的转储和地震图的现场绘制。该系统在野外试验期间已取得大量近震、远震及核爆炸记录。     

Probabilistic aftershock hazard assessment II: application of strong ground motion simulations

Probabilistic aftershock hazard assessment (PAHA) has been introduced by Wiemer (Geophys Res Lett 27:3405–3408, 2000). The method, in its original form, utilizes attenuation relations in evaluating peak ground velocity (PGV) exceedence probability. We substitute the attenuation relations together with their uncertainties by strong ground motion simulations for a set of scenarios. The main advantage of such an approach is that the simulations account for specific details of the aftershock source effects (faulting style, slip distribution, position of the nucleation point, etc.). Mean PGVs and their standard deviations are retrieved from the simulation results obtained by the new hybrid k-squared source model, and they are used for the PAHA analysis at a station under study. The model chosen for the testing purposes is inspired by the Izmit A25 aftershock (M _w  = 5.8) that occurred 26 days after the mainshock. The PAHA maps are compared with (1) those obtained by the use of attenuation relations and (2) the peak values of ten selected strong-motion recordings written by the aftershock at epicentral distances <50 km. We conclude that, although the overall hazard decay with increasing fault distance is similar, the PAHA maps obtained by the use of simulations exhibit remanent radiation pattern effect and prolongation in the strike direction due to the directivity effect pronounced for some of the scenarios. As regard the comparison with real data, we conclude that the PAHA maps agree with observed peak values due to appropriate attenuation model adopted in the analysis.     

Truncation of the distribution of ground-motion residuals

Recent studies to assess very long-term seismic hazard in the USA and in Europe have highlighted the importance of the upper tail of the ground-motion distribution at the very low annual frequencies of exceedance required by these projects. In particular, the use of an unbounded lognormal distribution to represent the aleatory variability of ground motions leads to very high and potentially unphysical estimates of the expected level of shaking. Current practice in seismic hazard analysis consists of truncating the ground-motion distribution at a fixed number (ε _max) of standard deviations (σ). However, there is a general lack of consensus regarding the truncation level to adopt. This paper investigates whether a physical basis for choosing ε _max can be found, by examining records with large positive residuals from the dataset used to derive one of the ground-motion models of the Next Generation Attenuation (NGA) project. In particular, interpretations of the selected records in terms of causative physical mechanisms are reviewed. This leads to the conclusion that even in well-documented cases, it is not possible to establish a robust correlation between specific physical mechanisms and large values of the residuals, and thus obtain direct physical constraints on ε _max. Alternative approaches based on absolute levels of ground motion and numerical simulations are discussed. However, the choice of ε _max is likely to remain a matter of judgment for the foreseeable future, in view of the large epistemic uncertainties associated with these alternatives. Additional issues arise from the coupling between ε _max and σ, which causes the truncation level in terms of absolute ground motion to be dependent on the predictive equation used. Furthermore, the absolute truncation level implied by ε _max will also be affected if σ is reduced significantly. These factors contribute to rendering a truncation scheme based on a single ε _max value impractical.     

乐山市地面风场特征及风能资源初探

利用乐山市1971~2005年整编风资料对乐山市各区县地面风场进行了全面分析,并对全市风能资源的分布情况进行了研究,旨在对今后乐山市风的预报及其相关服务有较好的帮助。     

西北地区降水对陆面特征敏感性的数值试验

本文是一个用大气环境模式研究中国西北地区陆面特征改变之后影响其降水的数值试验，模式中假定西北地区的植被完全被裸陆代替，对６、７、８月进行数值积分，以便检查夏季大气环流对陆面特征的响应，数值试验的结论是：陆面反照率升高后，与之相伴随的是降水率下降，并且大气的下沉运动控制了该地区。