Pacific Coast Of Tohoku Earthquake Research Articles

2011年東北地方太平洋沖地震による東京湾地域埋立地盤の変状 : 千葉市美浜区花見川緑地公園で見られた長大地割れ(フォト)

2011年東北地方太平洋沖地震による東京湾地域埋立地盤の変状 : 千葉市美浜区花見川緑地公園で見られた長大地割れ(フォト)

A Framework for Seismic Design of Items in Safety-Critical Facilities for Implementing a Risk-Informed Defense-in-Depth-Based Concept

Recently, especially after the 2011 off the Pacific coast of Tohoku Earthquake and the Fukushima Daiichi Nuclear Power Plant accident, the need for treating residual risks and cliff edge effects in safety-critical facilities has been widely recognized as an extremely important issue. In this paper, the sophistication of seismic designs in safety-critical facilities is discussed from the viewpoint of mitigating the consequences of accidents, such as the avoidance of cliff edge effects. For that purpose, the implementation of a risk-informed defence-in-depth-based framework is proposed in this study. A basic framework that utilises diversity in the dynamic characteristics of items and also provides additional seismic margin to items important for safety when needed is proposed to prevent common cause failure and to avoid cliff edge effects as far as practicable. The proposed method is demonstrated to be effective using an example calculation.

東京湾北部の埋立地における層序と2011年東北地方太平洋沖地震時の液状化－流動化の層準：船橋市日の出町での調査から

東京湾北部の埋立地における層序と2011年東北地方太平洋沖地震時の液状化－流動化の層準：船橋市日の出町での調査から

Sliding and overturning stability of breakwater under combined effect of earthquake and tsunami

Powerful tsunami waves were generated by the 2011 off the Pacific Coast of Tohoku Earthquake, and they struck the coast of Japan after few minutes of the main shock. Seismic aftershocks continued for several hours. Many coastal structures such as breakwaters, seawalls were damaged due to the earthquake and tsunami. It may be possible that some coastal structures were hit by the aftershock and the tsunami together. This paper focuses on this fact, and analyzes stability of breakwater under combined effect of earthquake and tsunami. For estimating seismic inertia forces on breakwater, the pseudo-dynamic method was used, which considers seismic waves passing through body of breakwater with respect to depth and time. Stability of breakwater was assessed in terms of factors of safety against sliding and overturning modes of failure. It was found that stability of breakwater reduces drastically under combined effect of earthquake and tsunami as compared to only earthquake and only tsunami. Parameters such as seismic accelerations, height of tsunami wave, seawater level and width of breakwater have significant impacts on stability of breakwater under combined action of earthquake and tsunami. The design charts and tables, presented in this paper, will be helpful for design engineer to design a breakwater under combined effect of earthquake and tsunami in future.

Experimental study of lightly reinforced concrete walls upgraded with various schemes under seismic loading

The 2011 off the Pacific coast of Tohoku Earthquake clarified the weakness of lightly reinforced concrete (RC) walls with opening (spandrel, wall pier, wing wall) in residential and government office buildings. Lightly RC walls are not a critical structural component, but their damage often impaired functions of buildings after earthquakes although it did not jeopardize safety. In order to avoid the suspension of building function due damage to lightly RC walls, it is very important to have proper upgrading schemes to improve the seismic performance. An experimental study was carried out on three full-scale wall specimens upgraded with various schemes to improve the seismic behavior of shear-type damage of lightly RC walls. Two specimens were upgraded using additional RC panel and ultra-high strength fiber reinforced concrete (UFC) panel to prevent shear failure. The other specimen had upgraded reinforcement details to increase shear capacity and flexural ductility. The test results were compared with past lightly RC wall test as a reference wall, which failed prematurely in shear reproducing the failure observed in the field. The changes of ultimate failure mode and the damage process were observed. Three upgraded specimens showed ductile and stable behavior with less damage compared with the reference wall. Adding RC and UFC panels improved the behavior of lightly RC wall and prevented crack formation at the central part of the wall panel. Increasing the amount of horizontal reinforcement and providing confinement in the boundary regions controlled the opening of crack width and made structure more ductile.

P21 2011年東北地方太平洋沖地震後の箱根火山における群発地震活動の特徴(ポスターセッション)

P21 2011年東北地方太平洋沖地震後の箱根火山における群発地震活動の特徴(ポスターセッション)

B2-02 2011年東北地方太平洋沖地震M9.0後の東北地方の火山活動 : 岩手・秋田駒ヶ岳火山,吾妻火山の地震活動を例として(地震と火山,口頭発表)

B2-02 2011年東北地方太平洋沖地震M9.0後の東北地方の火山活動 : 岩手・秋田駒ヶ岳火山,吾妻火山の地震活動を例として(地震と火山,口頭発表)

Development of Tsunami Fragility Functions for Ground-Level Roads

In exploring the relationship between ground-level road damage ratios and tsunami inundation depths following the 2011 Pacific Coast Tohoku earthquake in Japan, we focused on road damage components, excluding elevated roads, bridges, and tunnels. The damage ratio is defined as the number of damage incidents per kilometer. We used the damage dataset compiled by the Japanese Ministry of Land, Infrastructure and Transport. We propose four fragility function zones for ground-level roads based on differences in topographical features. We studied these zones based on numerical simulation results of tsunami propagation.

Dynamic Rupture Simulations Based on the Characterized Source Model of the 2011 Tohoku Earthquake

The 2011 Off the Pacific Coast of Tohoku earthquake (Tohoku earthquake, Mw 9.0) occurred on the Japan Trench and caused a devastating tsunami. Studies of this earthquake have revealed complex features of its rupture process. In particular, the shallow parts of the fault (near the trench) hosted large slip and long period seismic wave radiation, whereas the deep parts of the rupture (near the coast) hosted smaller slip and strong radiation of short period seismic waves. Understanding such depth-dependent feature of the rupture process of the Tohoku earthquake is necessary as it may occur during future mega-thrust earthquakes in this and other regions. In this study, we investigate the “characterized source model” of the Tohoku earthquake through dynamic rupture simulations. This source model divides the fault plane into several parts characterized by different size and frictional strength (main asperity, background area, etc.) and is widely used in Japan for the prediction of strong ground motion and tsunami through kinematic rupture simulations. Our characterized source model of the Tohoku earthquake comprises a large shallow asperity with moderate frictional strength, small deep asperities with high frictional strength, a background area with low frictional strength, and an area with dynamic weakening close to the trench (low dynamic friction coefficient as arising from, e.g., thermal pressurization). The results of our dynamic rupture simulation reproduce the main depth-dependent feature of the rupture process of the Tohoku earthquake. We also find that the width of the area close to the trench (equal to the distance from the trench to the shallow asperity, interpreted as the size of the accretionary prism) and the presence of dynamic weakening in this area have a significant influence on the final slip distribution. These results are useful to construct characterized source models for other subduction zones with different scale of the accretionary prism, such as the Chile subduction zone and the Nankai Trough. Dynamic rupture simulations based on the characterized source model might provide useful insights for hazard assessment associated with future mega-thrust earthquakes.

液状化による戸建て住宅沈下を定量的に予測するための簡易解析

A large settlement and tilting of detached house have been often observed due to ground liquefaction. In order to reduce the damage of the detached house, we have to predict the amount of deformation precisely. Finite element analyses with comprehensive constitutive models have been widely used for this purpose. However, quite a few material parameters in the constitutive model should be determined before the analysis. That process sometimes takes a long time and requires a high cost. In order to solve these problems, the authors have proposed a new numerical scheme based on the Lagrangian mesh free particle method with a very simple constitutive model. Model shaking table tests, validation analyses of liquefaction damage at Urayasu city during the 2011 off the Pacific coast of Tohoku Earthquake and prediction analyses of virtual ground model were also carried out. Based on a series of analysis, it was confirmed that the performance of the proposed method was very promising. The following shows the summary in present paper. 1) In chapter 2, conventional analytical and numerical methods are outlined, such as Building Standards Law, guideline and finite element analysis. Building Standards Law is found that we are able to get the bearing capacity of non-liquefied ground without consideration of ground liquefaction. The guideline is found to be able to obtain the possibility of ground liquefaction. However, it does not predict settlement or tilting of detached house. The finite element analysis with a comprehensive constitutive model can predict the settlement or tilting of detached house by ground liquefaction. However, limited number of engineers can handle those programs. Furthermore the standard penetration test is usually necessary to determine constitutive model parameters and its process is expensive for detached house owners. 2) In chapter 3, a new numerical scheme based on the Lagrangian mesh free particle method with a very simple constitutive model is summarized. In new numerical scheme, the Smoothed Particle Hydrodynamics (SPH) method capable of simulating large deformation is used to discretize the numerical area concerned in space. Furthermore, it is emphasized that the simple constitutive model needs a small number of mechanical parameters. 3) In chapter 4, model shaking tests are carried out to capture the localized deformation pattern of the ground next to the detached house during liquefaction. Then, we try to reproduce the localized deformation of the ground by using the proposed SPH scheme. The proposed numerical scheme is found to succeed in reproducing the localized settlement pattern of the model detached house quantitatively. 4) In chapter 5, a detached house severely damaged during the 2011 off the Pacific coast of Tohoku Earthquake is also targeted for the verification of the performance of the proposed SPH scheme. The proposed SPH scheme is found to reproduce a large settlement of a real detached house observed qualitatively. 5) Finally, in chapter 6, we try to predict the settlement of a detached house on the virtual ground by liquefaction using the proposed SPH scheme. Based on the virtual ground model simulation using proposed SPH scheme, it is found that we are able to predict the liquefaction damage level of the detached house. Furthermore it is confirmed that settlement of detached house is affected by Dcy and H1 from results of previous liquefaction judgment and proposed method.

東北地方太平洋沖地震に伴う津波が大槌湾のプランクトン群集に及ぼした影響

東北地方太平洋沖地震に伴う津波が大槌湾のプランクトン群集に及ぼした影響

2011年東北地方太平洋沖地震（Mw9.0）に関連する地磁気日変化異常の時空間的特徴

Recent studies have reported unusual behaviors of geomagnetic diurnal variation (GDV) in the vertical component prior to the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0). To make a better understanding of this phenomenon, time-spatial analysis of GDV has been applied in this study. Geomagnetic data of long term observations at 17 stations in Japan have been analyzed using the same method in Han et al. 2015. Ratios of diurnal variation range between the target station and the reference station KAK have been computed. After removing seasonal variations revealed by wavelet transform analysis, the 15-day mean values of the ratios in the vertical component shows a clear anomaly exceeding the statistical threshold about 2 months before the mega event in both ESA and MIZ stations in the Tohoku Region. Similar results could not be found in other regions of Japan. Spatial distributions of the ratios show a good agreement between the location of the anomalies and the epicenter of Mw 9.0 earthquake. These time-spatial results are consistent with independent results obtained from other observations such as radon density, seismicity, and GPS displacements, which suggest the geomagnetic data might be useful in earthquake monitoring and disaster mitigation.

アマモ場における魚類群集構造の津波前後の比較

アマモ場における魚類群集構造の津波前後の比較

2011年東北地方太平洋沖地震における強震動生成域からの長周期地震動

本研究は, 海溝型巨大地震を対象とした, 超高層ビルなどの長周期構造物の被害に影響する長周期地震動（2-10秒）のための震源モデルおよび評価手法の構築を目的としている．2011年東北地方太平洋沖地震（以下2011年東北地震と呼ぶ）の短周期地震動を生成したSMGA（強震動生成域）からの波群の地震動の解析により, それらの震源スペクトルは, 2-10秒の長周期帯域を含んでω-2則に従う特性を持っていることがわかった．すなわち, SMGAからの地震動は, SMGAの直径に対応するコーナー周波数をもち, それよりも高周波数でほぼω-2で減衰する．理論的グリーン関数を用いて, SMGAからの地震動を計算するには, SMGAを分割する小断層サイズおよびすべり速度関数の適切な選択が必要とされる．ここでは, すべり速度関数としてsmoothed ramp関数と中村・宮武（2000）の関数を用いて比較検討を行った．小断層サイズを小さくすると, 指向性効果などの破壊伝播の再現がより有効になるという利点があるが, 小さくしすぎると, どちらの関数を用いても高周波数域で, 観測で見られるω-2よりも大きく減衰し, 対象とする2-10秒の地震動が再現できない．同じ小断層サイズの時, ライズタイムの逆数の周波数よりも高周波数域では, 中村・宮武（2000）の関数に比べてsmoothed ramp関数はより大きく減衰する．中村・宮武（2000）の関数を用いて, 小断層を1×1 km2とし, 破壊伝播速度に10％の揺らぎを与えることにより, 強震動生成域からの地震動は周期1秒までほぼω-2の特性をもつことを確認した．上記のすべり時間関数, 小断層サイズ, および破壊伝播速度の揺らぎの組み合わせで2011年東北地震の時観測された2-10秒の長周期地震動が, 5つの強震動生成域からの足し合わせでほぼ再現できることがわかった．

PIXE analysis of stream water following the Mt. Hakone eruption on 30 June 2015 — temporal changes in elemental concentrations over two years

After the 2011 Off the Pacific Coast of Tohoku Earthquake on 11 March, 2011, volcanic activity in Japan was observed to increase. In this study, we use the PIXE method to analyze elemental concentrations in stream water flowing directly from the fumarolic area on Mount Hakone, which erupted on 30 June 2015. Throughout a two-year monitoring period following the eruption, concentrations of 12 dissolved elements were measured. We found that the stream water was strongly acidic. For one year after the eruption, the concentrations of magma-derived elements (S, Cl) and rock-derived elements (Al, Ca, Fe, K, Mg, Mn, and Na), except for Si, showed a clear decreasing trend. These measurements suggest that magmatic activity and fumarolic activity reduced gradually over one year. After this year-long period, elemental concentrations stopped decreasing and instead showed broadly flat levels with sporadic increases and decreases. However, throughout the year immediately following the eruption, the number of volcanic earthquakes was consistently at zero or close to zero. These different indications of volcanic activity suggest that the elemental concentrations in stream water may be more sensitive indicators of small changes in subterranean behavior than of the number of volcanic earthquakes.

平成23年（2011年）東北地方太平洋沖地震による液状化発生領域での表面波探査 ―千葉県香取市利根川北岸地区の例―

2011年3月11日に平成23年（2011年）東北地方太平洋沖地震が発生し，多くの被害が発生した。東京湾岸や利根川下流域では広範囲にわたって，液状化の被害を受けた。本研究では，利根川下流域にあたる千葉県香取市の利根川北岸地域で表面波探査を実施し，地下約30 mまでのS波速度（Vs）構造を求めた。その結果，調査領域の地下は，比較的高速度のVsを持つ砂質表層，低速度のシルト質層，高速度の砂質基盤層の三層に区分されることがわかった。

Study on evaluation of emergency water supply activity in Urayasu city when liquefaction occurred by the 2011 off the Pacific coast of Tohoku Earthquake

Study on evaluation of emergency water supply activity in Urayasu city when liquefaction occurred by the 2011 off the Pacific coast of Tohoku Earthquake

2011年東北地方太平洋沖地震に伴って観測された火山地域での局所的沈降に関する数値モデリング

2011年東北地方太平洋沖地震に伴って観測された火山地域での局所的沈降に関する数値モデリング

2011年東北地方太平洋沖地震による潮来市日の出地区の液状化被害と液状化層の粒度組成

2011年東北地方太平洋沖地震による潮来市日の出地区の液状化被害と液状化層の粒度組成

2011年東北地方太平洋沖地震による茨城県神栖市，鹿嶋市の液状化発生域と砂利採取場分布の変遷との関係

2011年東北地方太平洋沖地震による茨城県神栖市，鹿嶋市の液状化発生域と砂利採取場分布の変遷との関係