2004 Fiscal Year Final Research Report Summary
The effects of surface geometry tree and buildings on distribution of wave propagation
| Project/Area Number |
14350237
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
構造工学・地震工学
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| Research Institution | Saitama University |
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Principal Investigator |
IWASHTTA Kazuyoshi Saitama University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (40203377)
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| Co-Investigator(Kenkyū-buntansha) |
KAWAKAMI Hideji Saitama University, Geo-sphere Research Institute, Professor, 地圏科学研究センター, 教授 (50125887)
MOGI Hidenori Saitama University, Faculty of Engineering, Assistant Professor, 工学部, 講師 (80261882)
TANIYAMA Hisashi Saitama University, Faculty of Engineering, Research Associate, 工学部, 助手 (80236710)
SAITOH Masato Saitama University, Faculty of Engineering, Research Associate, 工学部, 助手 (40334156)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Earthquake / Strong motion / surface geometry / Vibration / Tree / Building / Wave Propagation / 強震動 |
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| Research Abstract |
It is well known that the most fundamental and important problem in the seismic engineering is estimation of the surface ground motion caused by earthquake. Usually, to evaluate the surface ground motion and wave propagation in the surface layer, the ground is modeled as the very simple flay layer system, while the real surface ground is quite irregularly shaped. And the programs, like as SHAKE, based on the wave propagation in simple layer system are applied. In those cases, the ground is assumed as flat and there is nothing on the surface. There are many local and micro geographical features on the ground surface. On the ground, there may be many trees, forests, houses and buildings. There is a possibility that wave propagation is affected these features, In this study, the effects of these omitted phenomena on the wave propagations are evaluated.
Seismic responses of a ground with various types of sinusoidal shaped irregularity were evaluated by using the boundary element method and
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analyzed based on "scattered-wave contribution". The examination of the numerical results revealed the following : 1)the response at the trough varies sharply with frequency whereas the response at the peak shows large amplification over a wide frequency range ; 2)the predominant frequencies at the trough depend on the amplitude of the surface irregularity and do not depend on the number of fluctuations of the ground ; and 3)these characteristics can be understood as the results of the interference of scattered waves coming from the irregular surface.
Peak ground acceleration(PGA) as a measure of earthquake motion intensity is an important factor in the earthquake-resistant design and reliability analysis of structures. The purpose of this article is to examine the spatial variability of PGAS (recorded at the same epicentral distance) as a function of separation distance. To do this, we define PGA ratios as spatial intraevent variations of PGAS and examine their statistical characteristics. We analyze the probability distribution of the ratios and formulate equations for their probability density functions, mean values, standard deviations, and percentiles. These statistics are then estimated using accelerometer arrays of the Chiba, SMART-1, and SIGNAL databases. Then, the relationship between these statistics and the station separation distances is analyzed. We found that the means and standard deviations have an almost linear relationship with the logarithm of the station separation distances ranging from several meters to 100 km. Finally, based on the fiftieth and ninety-fifth percentiles, the differences between PGAS at two different sites due to future earthquakes are discussed. Less
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Research Products
(29 results)
