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タイトル Dynamic response evaluation and seismic zoning of western Osaka plain under Nankai Trough and Uemachi fault assumed seismic motions
著者 Naung Htun Zin・Oula Aabkari・肥後陽介・三村 衛
出版 第54回地盤工学研究発表会発表講演集
ページ 55〜56 発行 2019/06/20 文書ID rp201905400028
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  • タイトル
  • Dynamic response evaluation and seismic zoning of western Osaka plain under Nankai Trough and Uemachi fault assumed seismic motions
  • 著者
  • Naung Htun Zin・Oula Aabkari・肥後陽介・三村 衛
  • 出版
  • 第54回地盤工学研究発表会発表講演集
  • ページ
  • 55〜56
  • 発行
  • 2019/06/20
  • 文書ID
  • rp201905400028
  • 内容
  • 0028D - 07第 54 回地盤工学研究発表会(さいたま市) 2019 年 7 月Dynamic response evaluation and seismic zoning of western Osaka plain underNankai Trough and Uemachi fault assumed seismic motionsSeismic response analysis, PGA amplification, Geo-informatics京都大学大学院工学研究科学生会員○Zin Naung HtunDatabase京都大学大学院工学研究科学生会員Aabkari Oula京都大学大学院工学研究科国際会員肥後陽介京都大学大学院工学研究科国際会員三村1. INTRODUCTIONOsaka plain consists of a widespread formation of softweak subsoil in an alteration of gravel sediments (Dg) andmarine clay layers (Ma) topped by sandy sediments (As) 1).The soft soils can influence the characteristics of groundshaking and cause strong amplification. Dynamic responseanalysis based on detailed geological information of theground will help estimate the shaking intensity for futureearthquakes. In this study, a total of 894 soil profiles scatteredaround Osaka’s western plane are obtained from Kansai Geoinformatics Database. A one-dimensional seismic responseanalysis is performed using DYNEQ2). Nankai Trough(TNN) and Uemachi Fault (UMT) input motion were used 3),and a zoning map was created based on their peak groundacceleration (PGA) amplification. From the results of the map,the regional tendencies of the soil’s behavior are inspected. Inaddition to that, the effects of local site conditions; such as soilproperties and model parameters are investigated.衛(UMT) is short, but the intensity is large, contrary to the trenchtype earthquake (TNN) which has a long duration and lowerintensity. It’s however to be noted that each 500m mesh hasits own acceleration waveform. The input waves cover a widerange of amplitudes. The acceleration ranges from 1.2 m/s2to 3.5 m/s2 for (TNN) and from 2.9 m/s2 to 13.2 m/s2 for(UMT). The analysis is two dimensional, both east-west(EW) and north-south (NS) components of the seismic wavesare used.2.3 Model ParametersThe results of different dynamic deformation test data inOsaka area were analyzed 4) and the HD model with theparameters on Table 1 was found to best fit the test data amongthe three models.ℎmax ℎ1,ℎ122. METHODOLOGY OF THE ANALYSES2.1 Analysis ModelThe soil profile is shown in Fig1. The input motion isoriginally defined at the base layer (Dg4). However, in orderto conduct the seismic response analysis with a detailed soilprofile calculation is performed in 2 steps:Step1: To insert the earthquake wave in the lower model. Thelower model is a 500m mesh with 50m thickness for eachelement starting from (Dg4) at the bottom to (Dg2) at the top.Step2: To use the obtained new wave for the dynamicresponse of the ground surface. The upper model is a 250mmesh with an element thickness of 1m starting from (Ma12)at the bottom to (As) at the top. For each four adjacent 250mmesh points the lower model (500m mesh) and the inputwaves are the same.2.2 Input motionOsaka region is expected to be affected by the anticipatedNankai Trough earthquake. Therefore, the anticipated (TNN)wave was chosen. In addition to that, Osaka region itself hasseveral seismically active faults among which one of the mostserious is Uemachi Fault. Therefore the anticipated (UMT)wave was chosen. The duration of the inland earthquakeTable 1. H-D model parameters.γMa13Dg1Ma120.0020420.83.00.0011520.91.20.0031619.22.31m ℎℎAs0.0028621.63.0Fig. 1. Analysis model.55 Fig. 2. Nankai Trough and Uemachi Fault earthquakes PGA amplification zoning mapsreferential shear strain means that the soil will behavenonlinearly under high shear stresses. The individual behaviorof layers was investigated through the maximum accelerationand shear modulus distribution with depth. Marine clay(Ma13) was found to be responsible for motion attenuationdue to its low shear modulus and referential strain, and marineclay (Ma12) is responsible for motion amplification due to itshigh referential strain.3. RESULTS AND DISCUSSIONThe analysis results show that the PGA amplification(Fig.2) varies between 1.0 and 4.4 for (TNN), and 0.3 and 2.7for (UMT). The soil amplifies greatly in the case of (TNN),but only slightly or even de-amplifies in the case of (UMT).Uemachi Fault earthquake deamplifies in the majority of thepoints. As the earthquake has a very large amplitude, it can beassumed that the soil is displaying a nonlinear behavior. Inorder to confirm this, (UMT) amplitude was reduced to the10th of the original wave in ten random points and a suddenincrease in PGA amplification was noticed. It can beconcluded that the deamplification is due to the nonlinearbehavior of the soil.On the other hand, it’s observed that the two earthquakesshow the same trend. The eastern area shows a strongamplification while the northern and western areas show acomparatively lower amplification.3.1 Resonance investigationResonance behavior is investigated and the natural periodof the soil and the predominant period of the wave werecompared for each region. The eastern area adjacent to themountains has thin sedimental deposits resulting in a shortnatural period of the soil, and the wave’s strongest componenthas a short period as well. The soil’s natural period and thewave’s predominant period match causing resonance withinthe soil. The periods only coincide in the eastern area whichexplains the exceptionally strong amplification.3.2 Effect of soil properties and model parametersLayer properties imply the layer’s shear modulus 𝐺 andmodel parameters imply the referential shear strain 𝛾 .A low4. CONCLUSIONDynamic deformation analysis is performed for 894 pointsthrough western Osaka area for two waves. (UMT) waveshows less amplification than (TNN) wave due to the soil’snonlinear behavior. The eastern area shows a largeamplification in response to both waves. It’s found to be dueto the resonance behavior and also due to the geologicalformation of the area. The eastern area has an absence ofmarine clay (Ma13) which attenuates the motion and apredominance of marine clay (Ma12) which amplifies themotion making it the area most prone to motion amplificationin western Osaka plain.REFERENCES1) Kansai Geo-informatiocs Network: New Kansai soil-Osaka plain toOsaka bay, 2017.2) Yoshida, N.: DYNEQ Manual, Revised version, 1995.3) Osaka government: Osaka Prefecture General Disaster PreventionMeasures Investigation, 2007.4) Goto, H. et al.: Influence of Dynamic Deformation CharacteristicsModel on the Nonlinear Response of the Ground, Kansai GeoSymposium, 2018.56
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