共查询到20条相似文献，搜索用时 31 毫秒
1.
The anisotropic attenuation of macroseismic intensity for a seismogenetic zone is dealt with using a new modelling of intensity distribution. The analysis, carried out starting from the intensity maps of the earthquakes of different seismogenetic zones of Central and Southern Italy, allows the determination of the attenuation coefficients for each seismogenetic zone by an anisotropic attenuation law. The obtained results show the reliability of the proposed modelling within seismic hazard evaluation studies. 相似文献
2.
A methodology for the anisotropic characterization of macroseismic fields is proposed, in order to evaluate seismic hazard, based on the real geometry of the isoseismals of the field. The proposed methodology, independent of the macroseismic intensity attenuation law, allows both for a single field and for several fields in the same source zone, the determination of minimum and maximum attenuation values and of the relative directions. 相似文献
3.
Hazard mapping based on macroseismic data considering the influence of geological conditions 总被引：1，自引：0，他引：1
The object of this study is to consider directly the influence of regional geological conditions on the assessment of seismic hazard. It is assumed that macroseismic data at individual locations contain, in an average way, the influence of geological conditions.A Data Base referring to 199 historical (5) and instrumental (194, in the 1947–1993 period) events with macroseismic information in 1195 locations of Portugal was built. For any given seismic event, whenever macroseismic information was available at a location (town, village, etc.), an EMS-92 intensity value was estimated. To each one of those locations a geological unit, representing the most common type of soil, was assigned, based on the Geological Portuguese Map at a scale 1:500 000; the geological units were grouped into three categories: soft, intermediate and hard soils.The Data Base was used to determine the attenuation laws in terms of macroseismic intensity for the three different geological site conditions, using multiple linear regression analysis. The reasonability of the laws was tested by (i) checking residual distributions and (ii) comparing the map of isoseismals of important earthquakes with the isoseismals generated by the attenuation curves derived for each one of the three different soil classes, taking into consideration the soil class of each site. The main results of attenuation modeling are: high dispersion on macroseismic intensity data; all the models predict intensity values, for short hypocentral distances, lower than the ones observed; and for some important analyzed earthquakes and for the observed range of distances, the models confirm the expectancy that macroseismic intensity increases from hard to soft soil.The approach to obtain the hazard assessment at each location consisted in the use of the attenuation law specifically derived for the class of soil of that particular location. This method, which considers the influence of the regional geology, was illustrated with the mapping of hazard for the country for several return periods. Comparison with previous maps not taking into consideration the regional geological conditions emphasizes the importance of this new parameter. It can be concluded that (i) soil segmentation is clearly the cause for hazard increase in the region to the north of Lisbon, especially at sites with soft and intermediate soils as the ones in lower Tagus valley; the maximum increase on hazard is, in any case, less than one degree; (ii) when geological conditions are disregarded in the attenuation regression analysis, hazard pattern is similar to the one obtained for the case of hard soil everywhere. 相似文献
4.
Macroseismic intensity attenuation for crustal sources on romanian territory and adjacent areas 总被引：1，自引：0，他引：1
A. Pantea 《Natural Hazards》1994,10(1-2):65-72
The macroseismic intensity attenuation (m.i.a.) laws for the main seismic provinces with crustal foci of the Romanian territory and adjacent areas were established. The input data consist of MSK-64 intensities of 18 earthquakes with epicentral/maximum intensity in the range V to X degrees (MSK scale), whose isoseismal maps were available.The attenuation was analyzed as a function of distance and azimuth and from the three main attenuation formulas (logarithmic, exponential, and power-law) (the last one was preferred, as it best fits the observed data) and, consequently, were used for each seismogenic region. The bulk of derived equations is intended to be further used in the assessment of the seismic hazards of Romania. 相似文献
5.
After describing attempts at perfecting a methodology for studying isotropic and anisotropic macroseismic fields in previous works, the authors here try to identify the causes of anisotropy in the context of the “new basement tectonics”.The seismic data are taken both from reconstructions of the macroseismic fields of historic events, by means of a critical analysis of the data, and from macroseismic fields of recent events surveyed by the authors. These data are correlated to the structural framework obtained through recent neotectonic studies and the lineament distribution traced on satellite images and using the “shadow” method. Generally the direction of elongation of the mesoseismic area is closely dependent on the source parameters and can be associated with recent and present-day systems outlined by the latest neotectonic studies.The best correlation is observed, however, with the lineament pattern obtained using the “shadow” method: the domains of the lineaments associated with the preferential trend of the macroseismic field show, in the rose diagram of cumulative number, values of prevalence and kurtosis higher than average; in the cumulative lengths diagram, on the other hand, they show prevalence maxima and, in particular, kurtosis maxima which are all the higher the more the anisotropic trend of field is accentuated. Using the “Giant Griffith Cracks” model for the lineaments, it can be deduced that the swarms refer to fracture systems with greater vertical development generated during the most recent tectonic phases.Finally, from a study of the dynamic characteristics of the elastic waves, that are the main agents responsible for macroseismic effects, it can observed that the wavelength order of magnitude is comparable with that of the linear parameters in the “warp” formed by the “Giant Cracks”. It can, thus, be deduced that the strong absorption of energy can be determined by the fracture swarm when the wave propagation occurs orthogonally to the swarm. 相似文献
6.
7.
8.
The assessment of seismic hazard at five selected sites in the Sannio-Matese region is based on the computer program SRAMSC. Owing to the extensive historical data base for the output parameter, the MSK intensiy is chosen. The seismicity model is made up of five narrow area seismic sources. Circular or elliptical macroseismic fields are assigned to individual sources. A generalized Kövesligethy equation is used for this purpose as the attenuation relationship. The study reveals similar and a rather high hazard at the sites at Benevento, Boiano, and Melfi, which are located in the zone of highest seismic activity. At the Pomigliano and Lucera sites, the assessed hazard is much lower. 相似文献
9.
M. D. Sharma 《Journal of Earth System Science》2005,114(4):411-419
Wave propagation is studied in a general anisotropic poroelastic solid saturated with a viscous fluid flowing through its
pores of anisotropic permeability. The extended version of Biot’s theory is used to derive a system of modified Christoffel
equations for the propagation of plane harmonic waves in such media. The non-trivial solution of this system is ensured by
a biquadratic equation whose roots represent the complex velocities of four attenuating quasi-waves in the medium. These complex
velocities define phase velocity and attenuation of each quasi-wave propagating along a given phase direction in three-dimensional
space. The solution itself defines the polarisations of the quasi-waves along with phase shift. The variations of polarisations
of quasi-waves with their phase direction, are computed for a realistic numerical model. 相似文献
10.
The main result of this work is to show that macroseismic intensity decay with distance strongly depends on the epicentral intensity. An attenuation law that takes this parameter into account is proposed for Metropolitan France, from the analysis of SISFRANCE macroseismic database. Such a model significantly reduces the difference between observed and theoretical intensities. A map of the attenuation variations is also set up for Metropolitan France. No major site effects are observed, but at a broad scale, young Alpine regions display a stronger attenuation than old Hercynian regions. To cite this article: P. Arroucau et al., C. R. Geoscience 338 (2006). 相似文献
11.
Sergio Espinosa 《Natural Hazards》1996,13(2):179-202
A probabilistic macroseismic hazard assessment has been done for Nicaragua. For this, the most complete catalogue for Central America, compiled by NORSAR in Norway has been used. In this catalogue, empirical intensity attenuation relations were found. Using these empirical relations, magnitudes were changed to epicentral intensities expected in sites where no intensities had been reported. The calculated intensities from a polygon surrounding Nicaragua were used to assess the macroseismic hazard in the region. For the whole polygon, the cumulative intensity frequency was calculated resulting in a b-value of 0.60 for an intensity interval of V–IX. The time completeness was also studied indicating that, for strong events causing higher intensities (I
0 VII), the catalogue is complete for events that have been recorded since 1840. The whole polygon was cut into independent seismotectonic regions where the statistical procedure (intensity frequency and time completeness) was done. 相似文献
12.
B. C. Papazachos Ch. A. Papaioannou B. N. Margaris N. P. Theodulidis 《Natural Hazards》1993,8(1):1-18
A semi-probabilistic approach to the seismic hazard assessment of Greece is presented. For this reason, a recent seismotectonic model for shallow and intermediate depth earthquake sources, based on historical as well as on instrumental data, was used. Different attenuation formulae were proposed for the macroseismic intensity and the strong ground motion parameters for the shallow and the intermediate focal depth shocks. The data were elaborated in terms of McGuire's computer program, which is based on the Cornell's method.A grid of equally spaced points at 20 km distance was made and the seismic hazard recurrence curves for various parameters of the seismic intensity was estimated for each point. Finally, seismic hazard maps for the area of Greece were compiled utilizing the entire range of recurrence curves. These maps depict areas of equal seismic hazard and for every area the analytical relations of the typeSI =f(Tm), whereSI is a seismic intensity parameter andTm is the mean return period, were determined. 相似文献
13.
For two different zonations of the Calabro-Sicilian region the macroseismic intensity attenuation parameters are computed using the Grandori model.Some modifications to this relation are proposed here in order to allow its applicability also to those cases in which the data set available for each source zone does not present three successive epicentral intensity levels (I
0) as required for its application.Maps of theoretical distribution of maximum expected intensities were plotted for both zonations adopted, in order to test the reliability, also using other attenuation models.The results of the analysis show how the proposed modifications to the Grandori relation allow the macroseismic intensity attenuation modelling even in cases in which only one intensity level is available.Finally, the comparison of theoretical maximum expected intensity distribution maps, computed for different attenuation models and seismogenic zonations, shows that the maps plotted using the Grandori model and the zonation adopted by G.N.D.T. (Gruppo Nazionale Difesa dai Terremoti - C.N.R. Italy) are more reliable. 相似文献
14.
考虑地基横观各向同性和非均匀性,建立孔隙率、密度、剪切模量及渗透系数同时随深度变化的非均匀饱和地基模型,模型中考虑参数间的耦连影响,并引入非均匀因子表征地基的不均匀程度。基于Biot多孔介质理论建立以土骨架位移和孔隙水压力为基本未知量的控制方程,采用微分算子法对控制方程进行解耦求解,推导出非均匀饱和地基中瑞利波的频散方程。将推导结果分别退化到均匀饱和地基和单一弹性地基,验证了结果的正确性。通过数值算例,对非均匀饱和地基中瑞利波的传播速度、衰减系数及位移分布进行分析。结果表明：在低频区,饱和地基的非均匀性对瑞利波传播速度、衰减和位移都有显著影响,质点运动轨迹也由此发生变化;随着频率的升高,这种影响逐渐减小,当频率趋于无穷大时,瑞利波速度收敛于弹性地基中的波速;地基非均匀性增大了瑞利波的传播阻抗性,瑞利波位移加速衰减,传播深度小于均匀饱和地基。随着非均匀性增大,质点竖向位移的衰减快于水平位移,这种差异造成质点椭圆运动轨迹的扁率减小。此外,地基中非均匀土层厚度越小,则地基非均匀程度越高,对瑞利波的传播影响越大。 相似文献
15.
在有限元素法分析的基础上,根据图版中数据对(地层视电阻率,介电常数)和(幅度衰减,相位差)之间的对应关系,给出了一种采用交汇解释图版的方法,可把随钻电磁测量的相位差和幅度衰减同时转换为地层视电阻率和地层介电常数。同时,通过三维数值模拟不同地层模型的仪器响应,系统地分析了地层各向异性、地层倾角和地层厚度等环境因素对随钻电磁测量视电阻率的影响,结果表明,地层倾角越小,地层厚度越大,测量结果也就越准确。同时绘制了相应的校正解释图版。 相似文献
16.
Isosieismal maps of the main Friuli shock and of three large aftershocks were compiled on the scale 1 : 1 million as a joint effort of seismologists from countries shaken by the earthquakes. All macroseismic fields are irregular and display different damping in different directions. Depths of foci and attenuation coefficients are calculated. 相似文献
17.
18.
我国公路泥石流病害严重，泥石流淤埋公路构建筑物是一类常见的公路泥石流病害类型。泥石流衰减动力学是防治泥石流淤埋病害的重要关键技术，也是泥石流运动学、动力学研究的核心问题之一。本文作者运用泥沙运动力学及流体力学原理，初步建立了泥石流固相颗粒和液相浆体的能量衰减条件，把泥石流衰减模式概化为两类，即能量抑制衰减和能量自由衰减；通过泥石流沉积模型试验，得到了不同粘度泥石流体的沉积扇变化形态，随着泥石流体粘度的增大，沉积扇边缘变陡、扩展范围变小、纵轴线长度减小等结论与实际情况吻合；初步建立了泥石流能量衰减速率计算方法。研究成果为防治公路泥石流病害奠定了基础。 相似文献
19.
几十年来,人们对地震波在真实介质中传播发生的衰减进行了理论与实践两方面研究。文中综述了前人工作,包括机制与测试工作,同时给以评论,指出对于传播距离与频率之间关系研究不够,并且对实测结果作物理解释较少。作者用VSP技术进行了不同距离上衰减与频率之间关系的研究,提出了反射补偿的具体方法,采用了多项式拟合技术,得到了近抛物线型衰减的结果。然后,利用波前压力与振动的固有频率思想对测试结果进行了讨论,得出一些有益的结论。 相似文献
20.
柔性防护网是防治泥石流灾害的重要工程措施之一,现有防治结构以闭口防护网形式为主,易发生堵塞且调控能力欠佳。为此,提出一种开口柔性防护网结构,并基于理论分析、物理模型试验开展了开口柔性防护网对泥石流的调控性能研究,推导泥石流速度衰减率、爬升高度和柔性防护网拦挡率的理论公式。结果表明：与闭口柔性防护网结构相比,该结构起到了良好的自清洁作用,且可有效调控泥石流速度峰值;所推导的无量纲理论公式计算结果与物理试验结果具有较好的一致性;速度衰减率、爬升高度和拦挡率主要由相对开口高度、无量纲流深、泥石流相对密度和弗罗德数控制;速度衰减率和拦挡率与相对开口高度呈负相关,与泥石流相对密度呈正相关,爬升高度与相对开口高度、相对密度均呈负相关。上述研究可为开口柔性防护网在泥石流防治工程中的应用提供理论及技术支持。 相似文献