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991.
应用小波伽略金方法,对Maxwell方程进行离散化,导出了DB2-MRTD算法的探地雷达3D差分公式、数值稳定性条件.在此基础上,开发了探地雷达MRTD(multi-resolution time domain)法正演模拟程序,该程序极大地提高了运算速度,改善了三维探地雷达正演方法,并利用该自制程序,对三角形金属体模型进行了正演模拟,得到了其相应的正演合成三维剖视图及切片图,通过对这些模拟结果进行分析,可以加深对三维雷达反射特征的认识,提高探地雷达探测的可靠性、准确度,同时也说明时域多分辨率法在探地雷达三维正演模拟中的有效性. 相似文献
992.
In the surface wind drift layer with constant momentum flux, two sets of the consistent surface eleva- tion expressions with breaking and occurrence conditions for breaking are deduced from the first in- tegrals of the energy and vortex variations and the kinetic and mathematic breaking criterions, then the expression of the surface elevation with wave breaking is established by using the Heaviside function. On the basis of the form of the sea surface elevation with wave breaking and the understanding of small slope sea waves, a triple composite function of real sea waves is presented including the func- tions for the breaking, weak-nonlinear and basic waves. The expression of the triple composite func- tion and the normal distribution of basic waves are the expected theoretical model for surface elevation statistics. 相似文献
993.
The Wenchuan earthquake of 12 May 2008 is the most destructive earthquake in China in the past 30 years in terms of property
damage and human losses. In order to understand the earthquake process and the geo-morphological factors affecting the seismic
hazard, we simulated the strong ground motion caused by the earthquake, incorporating three-dimensional (3D) earth structure,
finite-fault rupture, and realistic surface topography. The simulated ground motions reveal that the fault rupture and basin
structure control the overall pattern of the peak ground shaking. Large peak ground velocity (PGV) is distributed in two narrow
areas: one with the largest PGV values is above the hanging wall of the fault and attributed to the locations of fault asperities
and rupture directivity; the other is along the northwestern margin of the Sichuan Basin and caused by both the directivity
of fault rupture and the amplification in the thick sediment basin. Rough topography above the rupture fault causes wave scattering,
resulting in significantly larger peak ground motion on the apex of topographic relief than in the valley. Topography and
scattering also reduce the wave energy in the forward direction of fault rupture but increase the PGV in other parts of the
basin. These results suggest the need for a localized hazard assessment in places of rough topography that takes the topographic
effects into account. Finally, had the earthquake started at the northeast end of the fault zone and ruptured to the southwest,
Chengdu would have suffered a much stronger shaking than it experienced on 12 May, 2008.
Supported by the U.S. National Science Foundation (Grant Nos. EAR 0738779 and OCE 0727919), the National Basic Research Program
of China (Grant No. 2004CB418404), and partially by the National Nature Science Foundation of China (Grant No. 40521002) 相似文献
994.
Tomotaka Iwata Takao Kagawa Anatoly Petukhin Yoshihiro Ohnishi 《Journal of Seismology》2008,12(2):223-234
We constructed a prototype of the basin and crustal structure model for the Kinki area, southwest of Japan, for the simulation
of strong ground motions of hypothetical crustal and subduction earthquakes. We collected results of the deep seismic velocity
profiles obtained by the reflection experiments and seismic imaging results, which were conducted in the Kinki area. The obtained
profiles give underground velocity structures of the crust, from the surface to the subducting slab. We also gather the basin
velocity structure information of the Osaka, Kyoto, Nara, and Ohmi basins. To examine the applicability of the constructed
velocity structure model to the ground motion simulation, we simulated waveforms of an intermediate size event occurred near
the source area of the hypothetical subduction earthquakes. Simulated ground motions using the basin and crustal velocity
structure model are fairly well reproducing the observations at most of stations, and the constructed basin and crustal velocity
structure model is applicable for the long-period ground motion simulations. 相似文献
995.
Probabilistic aftershock hazard assessment II: application of strong ground motion simulations 总被引:1,自引:1,他引:0
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. 相似文献
996.
Haruko Sekiguchi Masayuki Yoshimi Haruo Horikawa Kunikazu Yoshida Sunao Kunimatsu Kenji Satake 《Journal of Seismology》2008,12(2):185-195
We studied the long-period ground motions in the Osaka sedimentary basin, Japan, which contains a 1- to 3-km thickness of
sediments and is the site of many buildings or construction structures with long-natural period. We simulated the broadband
ground motions likely to be produced by the hypothetical Nankai earthquake: the earthquake expected to give rise to the most
severe long-period ground motion within the basin. For the simulation, we constructed multiscale heterogeneous source models
based on the Central Disaster Management Council of Japan (CDMC) source model and adopted a hybrid computation method in which
long-period motion and short-period motion are computed using a 3-D finite difference method and the stochastic Green’s function
method, respectively. In computing long-period motions, we used a 3-D structure model of the crust and the Osaka sedimentary
basin. The ground motions are estimated to have peak velocities of 50–90 cm/s, prolonged durations exceeding 300 s, and long
predominant periods of 5–10 s in the area with great thickness of sediments. The predominant periods are in agreement with
an approximate evaluation by 4 H/V
s where H and V
s are the thickness of the sediment and the average S wave velocity, respectively. 相似文献
997.
A seismological overview of long-period ground motion 总被引:1,自引:1,他引:0
Long-period ground motion has become an increasingly important consideration because of the recent rapid increase in the number
of large-scale structures, such as high-rise buildings and oil storage tanks. Large subduction-zone earthquakes and moderate
to large crustal earthquakes can generate far-source long-period ground motions in distant sedimentary basins with the help
of path effects. Near-fault long-period ground motions are generated, for the most part, by the source effects of forward
rupture directivity. Far-source long-period ground motions consist primarily of surface waves with longer durations than near-fault
long-period ground motions. They were first recognized in the seismograms of the 1968 Tokachi-oki and 1966 Parkfield earthquakes,
and their identification has been applied to the 1964 Niigata earthquake and earlier earthquakes. Even if there is no seismogram,
we can identify far-source long-period ground motions through the investigation of tank damage by liquid sloshing. 相似文献
998.
Truncation of the distribution of ground-motion residuals 总被引:4,自引:3,他引:1
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. 相似文献
999.
1000.