On the Intensity Virtual Area Characterization in the Intensity Distribution Modelling by Macroseismic Planes

A procedure is proposed for the reconfiguration of the macroseismic planes relative to earthquakes that, being characterized by a reduced number of points of observed intensity due to a lack of information, or having the epicenter very close to the coastline, are characterized by an incomplete distribution of observed intensity levels. The design of a plurality of virtual areas, through which a distribution of intensity consistent with an anisotropic model of attenuation is depicted, allows a reliable determination of macroseismic parameters of the same seismic event.     

An Anisotropic Attenuation Law of Macroseismic Intensity Performed on Virtual Intensity Distribution of Seismogenic Zones

An anisotropic attenuation law, based on an anisotropic characterization of intensity distribution for seismogenic zones, is proposed. This approach, that distinguishes itself for its consistency to the observed data, initially reconfigured by filtering procedures, is particularly suitable for seismic hazard evaluation.     

Macroseismic Intensity Modelling of Earthquakes in Southern Spain: Attenuation and Tectonic Implications

A modelling of the observed macroseismic intensity of historical and instrumental earthquakes in southern Spain is proposed, with the aim of determining the macroseismic parameters for seismic hazard evaluation in a region in which the characterization of intensity distribution of seismic events shows different levels of difficulty referable to the complex faults system of the area in study. The adopted procedure allows an analytical determination of epicenters and principal attenuation directions of earthquakes with a double level of verification with reference to the maximum shaking area and structural lineaments of the region, respectively. The analyses, carried out on a suitable number of events, highlight, therefore, some elements for a preliminary characterization of a seismic zonation on the basis of the consistency between seismic intensity distribution of earthquakes and corresponding structural framework.     

The December 5th, 1456 Central Italy Earthquake: A Discussion of a Possible Reshaping of Intensity Distribution by Vectorial Modelling

--A study of the intensity distribution of the earthquake of December 5th 1456, which affected a large area of central and southern Italy was carried out, verifying, through a recently proposed methodology, the two hypotheses assumed by different authors for one single seismic event and three distinct and close ones. This methodology is based on a vectorial modelling of the macroseismic intensity distribution which aims at determining the epicentre and the principal (minimum and maximum) attenuation directions.¶The study was structured, considering each of the two assumed hypotheses, in a set of tests obtained for the macroseismic field and the intensity map, by analysing different configurations of the observed intensity distribution.¶The results obtained are in agreement with the hypothesis of the time coexistence of three distinct seismic events, for which the calculated epicentres and the principal attenuation directions are compatible with the observed intensity distribution and with the tectonic trend of the Apennine region, respectively.     

安徽及邻区地震烈度衰减关系研究

利用安徽及邻区15次地震的40条等震线资料,采用联合统计回归的方法,得到统计回归方程及地震烈度衰减关系．将此地震烈度衰减关系与其他烈度衰减关系进行对比,并结合地震烈度分布资料对衰减关系进行检验．认为本次统计回归所得的烈度衰减关系对安徽地区是适用的。     

江西及邻区地震烈度衰减关系研究

收集江西及邻区的地震烈度等震线资料,采用椭圆长、短轴联合衰减模型和近、远场补点与长轴可转向方法,建立了该地区的地震烈度衰减关系并进行了验证,结果表明,该衰减关系符合该地区历史和近代地震震害分布的地域性特点,可进一步应用于地震安全性评价、震害预测、损失快速评估等研究.     

关于"一致"地震动衰减规律的探讨

以我国中南地区烈度资料为例,用卡方正交回归烈度和震级的联合椭圆衰减模型,研究了烈度和震级相互转换的一致性问题,给出适合该地区的“一致”地震动衰减关系,并与常规方法得到的最小二乘结果进行比较,结果较为合理。该方法也可用于预测不同地区其它地震动参数衰减关系。     

Modelling of viscoacoustic wave propagation in transversely isotropic media using decoupled fractional Laplacians

A new wave equation is derived for modelling viscoacoustic wave propagation in transversely isotropic media under acoustic transverse isotropy approximation. The formulas expressed by fractional Laplacian operators can well model the constant-Q (i.e. frequency-independent quality factor) attenuation, anisotropic attenuation, decoupled amplitude loss and velocity dispersion behaviours. The proposed viscoacoustic anisotropic equation can keep consistent velocity and attenuation anisotropy effects with that of qP-wave in the constant-Q viscoelastic anisotropic theory. For numerical simulations, the staggered-grid pseudo-spectral method is implemented to solve the velocity–stress formulation of wave equation in the time domain. The constant fractional-order Laplacian approximation method is used to cope with spatial variable-order fractional Laplacians for efficient modelling in heterogeneous velocity and Q media. Simulation results for a homogeneous model show the decoupling of velocity dispersion and amplitude loss effects of the constant-Q equation, and illustrate the influence of anisotropic attenuation on seismic wavefields. The modelling example of a layered model illustrates the accuracy of the constant fractional-order Laplacian approximation method. Finally, the Hess vertical transversely isotropic model is used to validate the applicability of the formulation and algorithm for heterogeneous media.     

The Grandori model: Anisotropic formulation and its application in the plotting of seismic hazard maps

The seismic hazard for the Calabro-Sicilian area is evaluated using an anisotropic formulation of the Grandori attenuation law. For each macroseismic field two main directions are identified: minimum and maximum attenuation of the macroseismic intensity. The results of the investigation show that the anisotropic formulation improves the compatibility level of the model (with respect to the isotropic one) with the intensities observed and produces probabilistic expected intensities which compare favourably with the values of seismic history in the investigated area when the zonation defined by the Messina University research group was used.     

川滇分区地震烈度衰减特征研究

考虑到不同区域地震烈度衰减规律的差异性,本文通过分析川滇地区地震空间分布、震害及烈度分布特征,搜集并整理了1900年以来川滇地区的140个5级以上地震案例,利用联合椭圆衰减模型,结合川滇地区的地质构造特征,建立了川滇分区地震烈度衰减关系。对比结果表明：不同区域的地震烈度衰减存在显著差异,尤其是在M=5和M=7级时区域差别明显;同时,与已有成果的对比结果也可看出,滇西地区在M=7级时近场烈度明显偏低,而川西北及滇中地区在M=5级时虽与中国西部地区基本一致,但也均低于其它分区。上述结果对川滇地区地震灾害快速评估和地震应急具有重要参考价值。     

青海玛多7.4级地震烈度快速评估

利用青海地震烈度衰减模型和基于断层最短距离的地震动参数衰减模型对青海玛多7.4级地震的烈度分布进行快速评估,将评估结果与实际烈度图对比分析。研究结果表明:两种模型可以在地震正式速报后1分钟内得到地震烈度分布的快速评估结果,时效性强,可以在最短的时间内为应急指挥和救援工作提供参考;青海地震烈度衰减模型计算结果比较理想化,在大致范围上有一定的参考性,但在重灾区范围上与此次实际结果存在偏差;基于断层最短距离的地震动参数衰减模型的PGV-v_(S30)计算结果较青海地震烈度衰减模型更为精细,在高烈度区的评估中具有较好的实际应用价值;相较于冉洪流等研究的地表破裂与震级的经验关系,Wells等研究的经验关系在本次地震中的适用性更好。文章研究结果在此次实际地震应急响应中进行了应用,为政府应急指挥决策和应急救援提供了重要数据支撑。     

川滇地区走滑型地震烈度衰减特征研究

为分析走滑型地震的烈度衰减特征, 我们搜集并整理1900年以来川滇地区的145个5级以上震例和其中70个5级以上、 破裂方式以走滑型为主的典型震例, 利用联合椭圆衰减模型, 建立该区域此类型地震烈度衰减关系。 对比已有研究成果, 结果表明, 川滇地区破裂方式以走滑型为主的地震烈度衰减速度慢于西南地区, 可能与该地区地震破裂方式、 动力学过程等有关, 但与川滇地区和中国西部的衰减规律相比没有明显差异。 本文给出的烈度衰减关系在该区域此类地震的灾害快速评估和地震应急中具有一定参考价值, 其他区域的适用性需进一步分析。     

中国西部地区地震烈度衰减关系

本文收集了1991年之后我国西部地区71个地震的烈度等震线资料,并以此对1918—1989年间176次地震的烈度资料进行了补充,采用长、短轴椭圆模型重新拟合了西部地区的分区地震烈度衰减关系。结果表明,新疆区和川藏区2个统计单元内地震烈度衰减关系有显著不同,应作为不同的分区对待。同时与其他研究者给出的该地区地震烈度衰减关系的对比结果显示,本文结果合理可靠,体现了近、远场地震烈度分布的特点,适合于该地区工程地震研究和应用。     

利用地面破坏现象评定地震烈度的研究

本文系统地介绍了聚乙烯改性沥青的室内试验研究结果。低密度聚乙烯具有较好的改性效果，改性后的沥青及其沸合料的路用性能皆比基础沥青的好。本文还就聚乙烯的改性机理作了初步探讨。     

基于GIS的地震烈度定量化输入

无论是震害预测还是震害快速评估工作,都需要进行地震烈度定量化输入。通过地震烈度衰减关系,在地理底图上绘制地震烈度等震线,将地震影响烈度定量化到地理底图中的面与点中,从而为地震灾害快速评估提供依据。     

设定地震及其烈度影响判别

设定地震常用于震害预测、地震小区划和重大工程选址,烈度衰减模型反映了地震引起的地面震动及其影响的强弱程度分布。设定地震包括确定性和非确定性设定两种方法,确定性方法基于构造或历史地震,非确定性方法是基于概率危险性方法,用于估计区域或城市未来可能遭遇的地震危险。缺失等震线或震害记载不详的历史地震和概率设定地震都不能确切地反映地震破坏影响,借助于烈度衰减关系模型和GIS,可直观地判别其影响分布情况,便于设定地震的取舍。     

一种基于自适应方法的地震烈度圈自动勾画关键技术研究

地震烈度分布是震后灾害损失快速评估、应急救援和恢复重建工作开展的重要依据。目前地震烈度圈主要是由专家根据现场实地调查获得的烈度调查点,结合预评估烈度圈,采用GIS软件进行手动勾画得到。这种传统方法耗时耗力。提出一种基于自适应方法的地震烈度圈自动勾画方法,首先根据余震展布、居民地分布、断层属性等判断宏观震中位置,结合断裂带走向确定烈度圈长轴方向。在此基础上,利用星机地多源灾情信息融合后的最高离散烈度点生成包络线,将最高烈度与烈度圈面积的统计关系作为约束条件,运用自适应算法扩距得到最高烈度圈。在最高烈度圈的基础上,结合各级离散烈度点,基于上述方法,从高到低依次得到其他烈度圈。最后以九寨沟7.0级地震为例,实验结果表明,利用该方法能够自动生成烈度圈,利用震后获得的星机地多源灾情信息融合得到的离散烈度点生成的烈度圈准确度高于80%,有效提高地震烈度圈勾画的效率,可以为地震应急救援工作的快速开展提供支持。     

华北地区地震烈度衰减模型的建立

利用20世纪华北地区37次中强地震事件的89条等震线数据,拟合了该地区地震烈度衰减关系。主要选取了M≥5.0的地震事件。与以往的地震烈度衰减关系相比,在计算中强地震烈度时,精度上得到了相应地提高。充分反映了华北地区地震烈度衰减较慢的特点。     

利用烈度数据点估算中强历史地震震级与震中的方法研究

本文基于地震烈度数据点,用椭圆参数方程对烈度点空间分布进行最小二乘拟合,得到各烈度区椭圆烈度估计线,然后对烈度估计线进行统计回归,得到一组适用于青、甘、川、滇4省中强地震的椭圆烈度分布模型I=f（M,R）.基于所建烈度分布模型,联立考虑中心点和方向性的椭圆数学方程,代入全部烈度数据点估算地震震级和宏观震中.本文的试算震例表明了此方法的可行性,并进行了不确定性分析.利用该方法对明清时期4次烈度点较少的中强历史地震参数进行了估算,所得结果表明了此方法对历史地震有效.     

Analysis of macroseismic fields using statistical data depth functions: considerations leading to attenuation probabilistic modelling

Modelling seismic attenuation is one of the most critical points in the hazard assessment process. In this article we consider the spatial distribution of the effects caused by an earthquake as expressed by the values of the macroseismic intensity recorded at various locations surrounding the epicentre. Considering the ordinal nature of the intensity, a way to show its decay with distance is to draw curves—isoseismal lines—on maps, which bound points of intensity not smaller than a fixed value. These lines usually take the form of closed and nested curves around the epicentre, with highly different shapes because of the effects of ground conditions and of complexities in rupture propagation. Forecasting seismic attenuation of future earthquakes requires stochastic modelling of the decay on the basis of a common spatial pattern. The aim of this study is to consider a statistical methodology that identifies a general shape, if it exists, for isoseismal lines of a set of macroseismic fields. Data depth is a general nonparametric method for analysis of probability distributions and datasets. It has arisen as a statistical method to order points of a multivariate space, e.g., Euclidean space \({\mathbb {R}}^{p}\), \(p \ge 1\), according to the centrality with respect to a distribution or a given data cloud. Recently, this method has been extended to the ordering of functions and trajectories. In our case, for a fixed intensity decay \(\varDelta I\), we build a set of convex hulls that enclose the sites of felt intensity \(I_s \ge I_0 -\varDelta I\), one for each macroseismic field of a set of earthquakes that are considered as similar from the attenuation point of view. By applying data depth functions to this functional dataset, it is possible to identify the most central curve, i.e., the attenuation pattern, and to consider other properties like variability, outlyingness, and possible clustering of such curves. Results are shown for earthquakes that occurred on the Central Po Plain in May 2012, and on the eastern flank of Mt. Etna since 1865.