MF研究者総覧

研究者データベース

詳細
山中　悠資(ヤマナカ　ユウスケ)
理学研究院　附属地震火山研究観測センター
講師
researchmap個人ページ
Last Updated :2024/05/12

基本情報

所属

  • 理学研究院　附属地震火山研究観測センター

職名

  • 講師

学位

  • 博士(工学)（東京大学）

科研費研究者番号

  • 60815108

ORCID ID

J-Global ID

研究キーワード

  • 台風   高波   高潮   固有振動   数値計算   震源過程   地震   津波   

研究分野

  • 社会基盤（土木・建築・防災） / 防災工学
  • 自然科学一般 / 固体地球科学
  • 社会基盤（土木・建築・防災） / 水工学

担当教育組織

職歴

  • 2021年06月 - 現在 北海道大学大学院理学研究院附属地震火山研究観測センター 講師
  • 2017年10月 - 2021年05月 東京大学大学院工学系研究科社会基盤学専攻 助教
  • 2016年04月 - 2017年09月 日本学術振興会特別研究員(PD)
  • 2013年04月 - 2016年03月 日本学術振興会特別研究員(DC)

学歴

  • 2013年04月 - 2016年03月   東京大学大学院工学系研究科社会基盤学専攻(博士課程)
  • 2011年04月 - 2013年03月   東京大学大学院工学系研究科社会基盤学専攻(修士課程)
  • 2009年04月 - 2011年03月   長岡技術科学大学建設工学課程
  • 2004年04月 - 2009年03月   和歌山工業高等専門学校環境都市工学科

所属学協会

  • 日本地球惑星科学連合   日本地震学会   土木学会   

研究活動情報

論文

  • Yusuke Yamanaka, Yuichiro Tanioka
    Earth, Planets and Space 76 71 1 - 14 2024年05月10日 [査読有り][通常論文]
  • Yusuke Yamanaka, Kana Hashimoto, Yoshimitsu Tajima
    Coastal Engineering Journal 1 - 14 2023年11月14日 [査読有り][通常論文]
  • Yuichiro Tanioka, Yusuke Yamanaka
    Progress in Earth and Planetary Science 10 1 2023年10月08日 [査読有り][招待有り]
     
    Abstract This paper provides an overview of inverse studies that estimate earthquake source processes using tsunami-related data. Methods and techniques developed with those data associated with the 2004 Sumatra and 2011 Tohoku-oki earthquakes were reviewed. These events significantly impacted subsequent studies that focused on great historical earthquakes. Thus, recent advancements from studies on great historical earthquakes (M > 8) using old tsunami data, including documents and non-digital tsunami waveforms, have been reviewed. Another key earthquake was the 1700 Cascadia earthquake, and its source process was revealed using geological tsunami deposit data, which have led to a recent surge in prehistorical earthquake studies using tsunami deposit data. Considering this, the advancements in prehistorical earthquake studies have been reviewed. Finally, expected advancements in earthquake source process studies using tsunami-related data in the near future have been discussed.
  • Yumi Nakadai, Yuichiro Tanioka, Yusuke Yamanaka, Tatsuya Nakagaki
    Bulletin of the Seismological Society of America 2023年10月01日 [査読有り][通常論文]
  • Rinda Nita Ratnasari, Yuichiro Tanioka, Yusuke Yamanaka, Iyan E. Mulia
    Frontiers in Earth Science 11 2023年09月06日 [査読有り][通常論文]
     
    Present tsunami warning systems have been specialized for earthquake-generated tsunamis, but rapidly evaluating the tsunamis caused by volcanic eruptions and/or volcanic sector collapses remains a challenge. In this study, we applied a numerical model to the 2018 Anak Krakatau tsunami event, which was generated by the sector collapse, investigated a tsunami prediction skill by the model, and developed a real-time forecasting method based on a pre-computed database for future tsunamis accompanied by such eruption of Anak Krakatau. The database stores spatiotemporal changes in water surface level and flux, which are simulated under various collapse scenarios, for confined areas in the vicinity of potential source. The areas also cover the locations of observation stations that are virtually placed on uninhabited island surrounding the source area. During an actual volcanic tsunami event, a tsunami is expected to be observed at the observation stations. For real-time tsunami forecasting, the most suitable scenarios to reproduce the observed waveforms are searched quickly in the database. The precomputed results under the identified scenarios are further provided as input for rapid tsunami propagation simulation. Therefore, an effective real-time forecasting can be conducted to densely populated coastal areas located at a considerable distance from the source, such as the coasts of Java and Sumatra. The forecasting performance was examined by applying the method for three hypothetical collapse scenarios assuming different sliding directions. We demonstrated that the tsunamis along the coasts were successfully forecasted. Moreover, we showed that the combination of a pre-computed database and the existence of observation stations near the source area was able to produce appropriate tsunami forecasting for the coastal area even in a volcanic event.
  • Yusuke Yamanaka, Yuichiro Tanioka
    Progress in Earth and Planetary Science 9 1 2022年12月 [査読有り][通常論文]
     
    Abstract A tsunami generated by an earthquake that occurred off the east coast of Japan in 1611 was predominantly concentrated along the Sanriku Coast. The 1611 event produced its greatest observed tsunami height at Koyadori, 28.8 m, higher than that produced by other representative tsunamis at the same location such as the 2011 Tohoku and 1896 Meiji Sanriku tsunamis. The characteristics of the source that resulted in the remarkable tsunami height at Koyadori have been widely debated. In this study, we simulated the local intensification mechanism of the 1611 tsunami and derived some key characteristics of the earthquake that produced the intensification at Koyadori based on these results. First, we investigated the topographical inundation characteristics in representative areas on the Sanriku Coast, including Koyadori, by numerical means. By comparing the numerical results with the observed heights for the 1611 tsunami, we found that a simulated tsunami that was dominated by short-wave components yielded a promising reproduction of the observed heights. The development of a local resonance seemed a more likely cause for the observed local intensification at Koyadori than a single-pulse wave. These results suggested that the 1611 earthquake produced a tsunami dominated by short-wave components. Furthermore, the source must have been located far off the Tohoku coast near the Japan Trench axis to have had substantial short-wave components along the Sanriku Coast. Based on these findings, we constructed a source scenario for local intensification by investigating the characteristics of Green’s functions from single-point sources. The scenario involves two separate earthquake sources in shallow crustal areas at the plate interface of the subduction zone, resulting in a moment magnitude of 8.5. The tsunami produced by this source model, which reflected the characteristics of a tsunami earthquake, effectively reproduced the local intensification observed on the Sanriku Coast.
  • Yusuke Yamanaka, Takenori Shimozono
    Earth, Planets and Space 74 1 2022年12月 [査読有り]
     
    AbstractFor Japanese coastal communities along the Japan Sea, where the risk of earthquake-induced tsunamis is deemed lower than that along the Pacific Ocean, tsunami disaster mitigation strategies have not been sufficiently developed. This study estimated the tsunami inundation characteristics for three major Japanese coastal cities along the Japan Sea. Based on tsunami simulations for representative coastal areas, we aimed to identify common vulnerabilities, which included those suggested by previous studies and local governments, to develop disaster mitigation strategies. Comprehensive simulations for tsunami propagation and inundation were performed for coastal areas in Akita City, Sakata City, and Niigata City based on earthquake and tsunami source scenarios developed by the Japanese Government for the Japan Sea area. To demonstrate the effectiveness of the estimated inundation characteristics, tsunami inundation was simulated for each coastal area under varying tsunami source conditions (including excessive tsunami magnitude) with a high resolution of the topography and infrastructure. Natural sand dunes, ports with man-made breakwaters, and rivers with levees are typical topographical features found in urbanized and densely populated areas along the Japan Sea coastline. According to the simulated results, the dunes and port breakwaters contribute significantly to decreasing the total amount of tsunami inundation for the areas behind them. However, the presence of the breakwaters also increases the tsunami heights in the areas immediately beyond the ports. Additionally, even the areas protected by the dunes might be exposed to an inundation risk in which the tsunamis invade a river channel, causing it to overflow. These findings were common to the coastal areas, and could be generally applicable to tsunami inundation for all coastal areas along the Japan Sea. Based on these results, the enhancement of existing infrastructure such as breakwaters and river levees should be the priority measure within tsunami risk-mitigation strategies; these, combined with natural resources such as dunes, can effectively mitigate tsunami disasters. Graphical Abstract
  • 神保 壮平, 山中 悠資, 下園 武範
    土木学会論文集B2(海岸工学) 78 2 I_181 - I_186 2022年11月 [査読有り][通常論文]
  • 伊勢 拓人, 下園 武範, 山中 悠資
    土木学会論文集B2(海岸工学) 78 2 I_211 - I_216 2022年11月 [査読有り][通常論文]
  • Yusuke Yamanaka, Takenori Shimozono
    Coastal Engineering Journal 1 - 17 2022年04月03日 [査読有り]
  • Yuichiro Tanioka, Yusuke Yamanaka, Tatsuya Nakagaki
    Earth, Planets and Space 74 1 2022年04月 [査読有り][通常論文]
     
    Abstract A large eruption of the Hunga Tonga-Hunga Haʻapai volcano in Tonga on January 15, 2022 generated air–sea coupled tsunamis observed at the ocean-bottom pressure sensor network along the Japan Trench (S-net) in Japan. Initial tsunamis from the 2022 Tonga eruption, detected by 106 ocean-bottom pressure sensors, were well modeled by an air–sea coupled tsunami simulation, with a simple atmospheric pressure pulse as sine function, having a half-wavelength of 300 km and a peak amplitude of 2 hPa. A one-dimensional air–sea coupled tsunami simulation having a simple bathymetry shows that an input atmospheric pressure pulse with a short half-wavelength of 50 km, which is shorter than the length of the ocean bottom slopes, caused an amplitude increase via the Proudman resonance effect near the deep trench. The wavefront distortion due to the separation of the air–sea coupled wave propagating with a speed of 312 m/s and tsunami propagating with that of $$\sqrt{gd}$$, where g is gravity acceleration and d is the ocean depth, is also significant near the shore. In contrast, these effects are not significant for the half-wavelength of the input atmospheric pressure pulse of 300 km. These results indicate that the air–sea coupled tsunami propagating through the trench is sensitive to the wavelength of an atmospheric pressure pulse. Graphical Abstract
  • Yusuke Yamanaka, Yoshimitsu Tajima
    Coastal Engineering Journal 64 1 1 - 16 2021年11月28日 [査読有り]
     
    The tide gauge data at Shirahama in Tanabe Bay on the Wakayama coast during Typhoons Jebi and Trami in 2018 showed two dominant oscillation components with periods of approximately 40–45 min and 7 min. We investigated the characteristics of the unique resonances using wavelet analysis and numerical simulations. Through the numerical simulation of storm surges by Jebi and Trami and the modeling of Trami with different tracks, we found that oscillations having a period of 40–45 min were primarily induced by the resonance in large areas, including Tanabe Bay and Kii Strait, which is north of the bay. The amplification of this large-scale resonance was sensitive to the forward speed and angle of the typhoon tracks. In addition, Green’s functions were developed to investigate local resonant characteristics in Tanabe Bay. The spatial distributions of the amplitude and phase difference of Green’s functions at different locations showed that the observed 7-min oscillations were amplified by the resonance of two adjacent small inlets at the Shirahama tide gauge station. The resonance between these two local inlets produced a long-lasting ~7-min oscillation observed at the tide gauge.
  • Yusuke Yamanaka, Yuichiro Tanioka
    Journal of Geophysical Research: Solid Earth 126 5 e2020JB021375  2021年04月02日 [査読有り][通常論文]
     
    A tsunami that followed the 1906 Colombia-Ecuador megathrust earthquake was observed and recorded by several tide gauges. In this study, tide gauge records were first digitized from documents comparing the estimated astronomical tide level changes, and the observed tsunami waveforms were extracted. An inverse analysis was conducted using the observed tsunami waveforms, and we successfully developed a slip distribution model that produced improved tsunami waveforms for tide gauge stations compared with previous studies. Based on a comparison of the developed source model and ruptured areas of other significant earthquakes around Colombia and Ecuador, the 1906 earthquake already ruptured an area affected by the 1979 earthquake, resulting in a substantial release of accumulated slip deficits. In contrast, although the ruptured area of the 1906 earthquake likely covered the source areas of the 1958 and 1942 earthquakes, the release in these areas during the earthquake was moderate and insignificant, and large slip deficits remained after the 1906 earthquake. These results demonstrate that the extent of the release of accumulated slip deficits varied greatly in the source area of the 1906 earthquake.
  • Yusuke Yamanaka, Miyuki Nakamura
    Earth, Planets and Space 72 1 :6  2020年12月 [査読有り][通常論文]
  • 野田智也, 山中悠資, 田島芳満, 小関健斗
    土木学会論文集B2(海岸工学) 76 2 I_691 - I_696 2020年11月 [査読有り]
  • 佐藤愼司, 野口賢二, 山中悠資, 与那嶺瑞輝
    土木学会論文集B2(海岸工学) 76 2 I_571 - I_576 2020年11月 [査読有り]
  • 山中悠資, 島津希来, 下園武範, 檜垣敬真
    土木学会論文集B2(海岸工学) 76 2 I_271 - I_276 2020年11月 [査読有り]
  • Jumpei Morioka, Yoshimitsu Tajima, Yusuke Yamanaka, Magnus Larson, Yoshiaki Kuriyama, Takenori Shimozono, Shinji Sato
    Coastal Engineering Journal 62 2 317 - 335 2020年05月 [査読有り][通常論文]
  • Yuichiro Tanioka, Amilcar Geovanny Cabrera, Greyving Jose Aguello, Yusuke Yamanaka
    Coastal Engineering Journal 62 3 405 - 412 2020年03月 [査読有り][通常論文]
     
    In 2018, a large earthquake (Mw7.6) occurred in the Swan Island Fault zone at the northwest boundary of the Caribbean plate. This earthquake generated a small tsunami of 20 cm. However, Puerto Cortes in Honduras is located close to the Swan Island Fault zone. Evaluation of tsunami hazard at Puerto Cortes due to large earthquakes along the fault zone is important. We first estimated the fault parameters of the 2018 Swan Island earthquake using W-phase inversion technique. Then, the moment magnitude of 7.6, the fault length of 134 km, the fault width of 24 km, and the slip amount of 5.1 m were estimated. In addition to those estimates, a small fault dimension of the earthquake, 40 km x 20 km, with a slip amount of 20.8 m was considered. Those two fault models were used to compute tsunami inundation at Puerto Cortes. The tsunami computed from the small fault inundated a large area in Puerto Cortes including the port area. The effect of co-seismic horizontal displacement of ocean floor also enhanced the tsunami inundation at Puerto Cortes. Those results indicate that preparation for future tsunami hazard in Puerto Cortes is important although no significant tsunami was generated historically.
  • Naohiro Hattori, Yoshimitsu Tajima, Yusuke Yamanaka, Kenzo Kumagai
    Coastal Engineering Journal 62 2 182 - 197 2020年02月 [査読有り][通常論文]
     
    Typhoon Jebi struck Osaka Bay, Japan, on September 4, 2018. It recorded the highest storm surge level ever in the inner part of Osaka Bay and caused severe damage to many coastal areas. Minami-Ashiyahama, Hyogo Prefecture, suffered from severe inundation by overtopping waves induced by the typhoon. The inundation volume was estimated through numerical simulation and the results suggested that the wave overtopping rate is highly sensitive to the tide level and could have been 1.5 ~ 2 times larger with water level rise of 50 cm at 4.5 m wave height. A video taken at Minami-Ashiyahama captures overtopping waves entering the residential area. The analysis of the video suggests the pattern of overtopping changing before and after peak tide level, and indicates the influence of slowly varying water level fluctuations including infragravity waves on the inundation volume. Spectral analysis of observed data at tide gauge stations were then conducted. The results show long wave components developing just before peak tide level, and suggests the influence of long waves to coastal disasters. A numerical simulation also suggested that the bay-scale and harbor-scale resonance of long wave components could have influenced the inundation characteristics at Minami-Ashiyahama.
  • Yusuke Yamanaka, Yoshinao Matsuba, Yoshimitsu Tajima, Ryotaro Shibata, Naohiro Hattori, Lianhui Wu, Naoko Okami
    Journal of Marine Science and Engineering 7 11 413 - 413 2019年11月 [査読有り][通常論文]
     
    In this study, field surveys along the coasts of Wakayama Prefecture, Japan, were first conducted to investigate the coastal damage due to storm surges and storm-induced waves caused by the 2018 Typhoons Jebi and Trami. Special focus was placed on the characteristic behavior of nearshore waves through investigation of observed data, numerical simulations, and image analysis of video footage recorded on the coasts. The survey results indicated that inundation, wave overtopping, and drift debris caused by violent storm-induced waves were the dominant factors causing coastal damage. Results of numerical simulations showed that heights of storm-induced waves were predominantly greater than storm surge heights along the entire coast of Wakayama in both typhoons. However, computed gradual alongshore variations in wave and surge heights did not explain locally-concentrated inundation and run-up heights observed along the coasts. These results indicate that complex nearshore hydrodynamics induced by local nearshore bathymetry might have played a significant role in inducing such local wave characteristics and the associated coastal damage. Analysis of video footage recorded during Typhoon Jebi, for example, clearly showed evidence of amplified infragravity wave components, which could enhance inundation and wave run-up.
  • 柴田涼太郎, 佐藤愼司, 山中悠資
    土木学会論文集B2(海岸工学) 75 2 1261 - 1266 2019年10月 [査読有り][通常論文]
  • 小関健斗, 山中悠資, 田島芳満, 下園武範
    土木学会論文集B2(海岸工学) 75 2 841 - 846 2019年10月 [査読有り][通常論文]
  • Yusuke Yamanaka
    Proceedings of the 10th International Conference on Asian and Pacific Coasts, APAC2019 199 - 206 2019年09月 [査読有り][通常論文]
  • Naohiro Hattori, Shinji Sato, Yusuke Yamanaka
    Coastal Engineering Journal 61 3 308 - 320 2019年07月03日 [査読有り][通常論文]
  • Nobuhito Mori, Tomohiro Yasuda, Taro Arikawa, Tomoya Kataoka, Sota Nakajo, Kojiro Suzuki, Yusuke Yamanaka, Adrean Webb, Tomoyuki Takahashi, Sooyoul Kim, Susumu Araki, Yoko Shibutani, Takashi Yamano, Daiki Sakai, Tomohiro Takagawa, Naoki Tsuruta, Shingo Kawaguchi, Syota Asahi, Takashi Fujiki, Takumu Iwamoto, Yu Chida, Tomoya Shibayama, Miguel Esteban, Tomoyuki Takabatake, Ryota Nakamura, Kohji Uno, Tetsuya Kakinoki, Yasuo Nihei, Daisuke Inazu, Takaaki Shigematsu, Kazunori Sameshima, Kazuhiko Honda, Daiki Satomura, Ibuki Tsujisawa, Kentaro Kumagai, Noriki Sugahara, Shoichi Emoto, Yoshimitsu Tajima
    Coastal Engineering Journal 61 3 278 - 294 2019年07月03日 [査読有り][通常論文]
     
    © 2019 Japan Society of Civil Engineers. Typhoon Jebi in 2018 caused severe damage along areas of Osaka Bay, Japan. After the storm, a Japan Society of Civil Engineers (JSCE) coastal survey group surveyed the coastal impacts and recorded watermarks inside Osaka Bay and along the Pacific. The maximum storm tide recorded by a tide gauge was 3.29 m at the Osaka Tide Station, which is a historical high for Osaka Bay. Coastal flooding consisted of both storm surge and wave run-up in almost all locations, with flooding exceeding 5 m and 12 m in elevation from mean sea level in the inner parts of Osaka Bay and along the Pacific coast, respectively. Coastal damage was severe in areas located outside of coastal barriers, such as ports and harbors, while residential areas were mainly well protected and spared due to coastal protection systems. In addition, some inland flooding occurred in the Kobe-Ashiya regions due to the storm surge propagating up several small rivers. This survey report summarizes the findings of the post-event survey by JSCE and analyzes the relation between maximum water level and resulting damage.
  • Mayu Inoue, Yuichiro Tanioka, Yusuke Yamanaka
    GEOSCIENCES 9 7 310  2019年07月 [査読有り][通常論文]
     
    A dense cabled observation network, called the seafloor observation network for earthquakes and tsunami along the Japan Trench (S-net), was installed in Japan. This study aimed to develop a near-real time tsunami source estimation technique using the ocean bottom pressure data observed at those sensors in S-net. Synthetic pressure waveforms at those sensors were computed for 64 earthquake tsunami scenarios with magnitude ranging between M8.0 and M8.8. The pressure waveforms within a time window of 500 s after an earthquake were classified into three types. Type 1 has the following pressure waveform characteristic: the pressure decreases and remains low; sensors exhibiting waveforms associated with Type 1 are located inside a co-seismic uplift area. The pressure waveform characteristic of Type 2 is that one up-pulse of a wave is within the time window; sensors exhibiting waveforms associated with Type 2 are located at the edge of the co-seismic uplift area. The other pressure waveforms are classified as Type 3. Subsequently, we developed a method to estimate the uplift area using those three classifications of pressure waveforms at sensors in S-net and a method to estimate earthquake magnitude from the estimated uplift area using a regression line. We systematically applied those methods for two cases of previous large earthquakes: the 1952 Tokachi-oki earthquake (Mw8.2) and the 1968 Tokachi-oki earthquake (Mw8.1). The locations of the large computed uplift areas of the earthquakes were well defined by the estimated ones. The estimated magnitudes of the 1952 and 1968 Tokachi-oki earthquakes from the estimated uplift area were 8.2 and 7.9, respectively; they are almost consistent with the moment magnitudes derived from the source models. Those results indicate that the tsunami source estimation method developed in this study can be used for near-real time tsunami forecasts.
  • Ryotaro Shibata, Shinji Sato, Yusuke Yamanaka
    Coastal Engineering Journal 61 2 256 - 265 2019年04月03日 [査読有り][通常論文]
  • Yuichiro Tanioka, Mizuho Shibata, Yusuke Yamanaka, Aditya Riadi Gusman, Kei Ioki
    PROGRESS IN EARTH AND PLANETARY SCIENCE 6 30 2019年03月 [査読有り][通常論文]
     
    The 2011 Tohoku-oki earthquake generated a large tsunami that caused catastrophic damage along the Pacific coast of Japan. The major portion of the damage along the Pacific coast of Tohoku in Japan was mainly caused by the first few cycles of tsunami waves. However, the largest phase of the tsunami arriving surprisingly late in Hakodate in Hokkaido, Japan; that is, approximately 9h after the origin time of the earthquake. It is important to understand the generation mechanism of this large later phase. The tsunami was numerically computed by solving both linear shallow water equations and non-linear shallow water equations with moving boundary conditions throughout the computational area. The later tsunami phases observed on southern Hokkaido can be much better explained by tsunami waveforms computed by solving the non-linear equations than by those computed by solving the linear equations. This suggests that the later tsunami waves arrived at the Hokkaido coast after propagating along the Pacific coast of the Tohoku region with repeated inundations far inland or reflecting from the coast of Tohoku after the inundation. The spectral analysis of the observed waveform at Hakodate tide gauge shows that the later tsunami that arrived between 7.5 and 9.5h after the earthquake mainly contains a period of 45-50min. The normal modes of Hakodate Bay were also computed to obtain the eigen periods, eigenfunctions, and spatial distribution of water heights. The computed tsunami height distributions near Hakodate and the fundamental mode of Hakodate Bay indicate that the large later phases are mainly caused by the resonance of the bay, which has a period of approximately 50min. The results also indicate that the tsunami wave heights near the Hakodate port area, the most populated area in Hakodate, are the largest in the bay because of the resonance of the fundamental mode of the bay. The results of this study suggest that large future tsunamis might excite the fundamental mode of Hakodate Bay and cause large later phases near the Hakodate port.
  • Yusuke Yamanaka, Shinji Sato, Takenori Shimozono, Yoshimitsu Tajima
    Coastal Engineering Journal 61 2 187 - 198 2019年02月 [査読有り][通常論文]
     
    The aim of this study is to estimate how and what kinds of tsunamis are generated near shorelines in the Japan Sea, using earthquake tsunami sources proposed by the Japanese government. Tsunami propagation based on these sources was first simulated based on the linear Boussinesq theory for Miho Bay, where a historical tsunami inundated the shoreline. The results indicate that tsunami sources not only near the bay but also farther from the bay could generate significant tsunami fluctuations. Thus, the amplification of the latter tsunamis was examined using Fourier analysis. Tsunami waveforms in the bay periodically fluctuate with large amplitudes after the first wave. The Fourier analysis specified these periods to be 13-16 min, consistent with the estimated resonance periods of the bay. Therefore, it can be concluded that one of the factors responsible for the amplification of tsunamis in Miho Bay is the bay-scale resonance. To investigate why resonance occurs during tsunamis, a relationship between the tsunami source geometry and the generated tsunami was examined. This analysis indicates that specific tsunami sources located in critical areas could enhance the resonance in Miho Bay.
  • Lianhui Wu, Yoshimitsu Tajima, Yusuke Yamanaka, Takenori Shimozono, Shinji Sato
    Coastal Engineering Journal 61 2 152 - 172 2018年12月 [査読有り][通常論文]
  • Yusuke Yamanaka, Yuichiro Tanioka
    Geophysical Journal International 214 3 1937 - 1946 2018年09月 [査読有り][通常論文]
     
    The megathrust earthquake that occurred along the Nazca Plate, near the coasts of Colombia and Ecuador in 1906, induced a large tsunami that propagated over the Pacific Ocean. The tsunami arrived in countries very far from the source region, including the United States and Japan. Part of the land covered by railroad tracks in Hilo Bay, Hawaii, United States, was inundated during the tsunami. The tsunami reached a height of several tens of centimetres in other regions of Hawaii, while residents in Hilo witnessed a height of 3.6 m in the bay. This study aimed to estimate the large amplification and inundation mechanisms of the 1906 Colombia-Ecuador tsunami in Hilo Bay, based on a detailed numerical simulation. First, available tsunami observation data were carefully examined and compared with the results of previous studies. The results indicate a maximum inundation height due to the tsunami in Hilo Bay ranging from 1.1 to 1.8 m. Next, a tsunami inundation simulation was performed under varying conditions, such as energy loss by bottom friction and tide level change, using an earthquake source model. The simulated results were consistent with the observation in terms of the inundation height and indicate that bay-scale resonance occurred in Hilo Bay. Furthermore, waves amplified by resonance were more significant than the primary wave. It can therefore be concluded that bay-scale resonance enhanced the tsunami inundation in Hilo Bay. These new results show that the tsunami magnitude of 8.7, estimated in a previous study, is an overestimation. Instead, the results suggest a lower tsunami magnitude of 8.4, which is consistent with the moment magnitude obtained from the earthquake source model.
  • Yuichiro Tanioka, Amilcar GC Ramirez, Yusuke Yamanaka
    Pure and Applied Geophysics 175 4 1363 - 1370 2018年04月 [査読有り][通常論文]
     
    The 2016 El Salvador-Nicaragua outer-rise earthquake (M-w 6.9) generated a small tsunami observed at the ocean bottom pressure sensor, DART 32411, in the Pacific Ocean off Central America. The dispersive observed tsunami is well simulated using the linear Boussinesq equations. From the dispersive character of tsunami waveform, the fault length and width of the outer-rise event is estimated to be 30 and 15 km, respectively. The estimated seismic moment of 3.16 x 10(19) Nm is the same as the estimation in the Global CMT catalog. The dispersive character of the tsunami in the deep ocean caused by the 2016 outer-rise El Salvador-Nicaragua earthquake could constrain the fault size and the slip amount or the seismic moment of the event.
  • Yusuke Yamanaka, Shinji Sato, Takenori Shimozono, Yoshimitsu Tajima
    Coastal Engineering Journal 60 1 22 - 38 2018年01月 [査読有り][通常論文]
     
    © 2018 Japan Society of Civil Engineers. Tsunami fission generates short waves at the front face of tsunami and these short waves may expand the inundation area, increase the hydrodynamic forces exerted on structures, and amplify the damage to coastal communities. It is therefore important to understand to what extent the tsunami fission generates such short wave components under variable conditions for development of better tsunami disaster mitigation strategies and plannings. This study carried out numerical experiments to describe under which conditions the tsunami fission occurs in a bay. The experiments indicated that the amplification of the nearshore tsunami height induced by the narrowing bay geometry and the bay-scale resonance enhance the tsunami fission. Based on the computations, a parametric diagram for the occurrence of tsunami fission was proposed in terms of the tsunami properties, the effect of bay geometry and the bay resonance. The developed diagram was applied to Sendai, Ryori, Yoshihama, and Toni Bays, which were affected by the 2011 Tohoku Tsunami. The proposed diagram consistently explained the occurrence of tsunami fission in Sendai Bay and in Ryori Bay as observed in the video footage. The diagram also suggested that the tsunami fission would have occurred in Yoshihama Bay. A high-resolution numerical computation was performed to simulate the tsunami deformation in the Yoshihama Bay and Toni Bay based on a nonlinear dispersive wave model. The result supported the validity of the diagram in describing the generation of tsunami fission in Yoshihama Bay.
  • Yusuke Yamanaka, Yuichiro Tanioka, Takahiro Shiina
    EARTH PLANETS AND SPACE 69 163 2017年12月 [査読有り][通常論文]
     
    The 1906 Colombia-Ecuador earthquake induced both strong seismic motions and a tsunami, the most destructive earthquake in the history of the Colombia-Ecuador subduction zone. The tsunami propagated across the Pacific Ocean, and its waveforms were observed at tide gauge stations in countries including Panama, Japan, and the USA. This study conducted slip inverse analysis for the 1906 earthquake using these waveforms. A digital dataset of observed tsunami waveforms at the Naos Island (Panama) and Honolulu (USA) tide gauge stations, where the tsunami was clearly observed, was first produced by consulting documents. Next, the two waveforms were applied in an inverse analysis as the target waveform. The results of this analysis indicated that the moment magnitude of the 1906 earthquake ranged from 8.3 to 8.6. Moreover, the dominant slip occurred in the northern part of the assumed source region near the coast of Colombia, where little significant seismicity has occurred, rather than in the southern part. The results also indicated that the source area, with significant slip, covered a long distance, including the southern, central, and northern parts of the region.
  • 山中悠資, 田島芳満
    土木学会論文集B2(海岸工学) 73 2 391 - 396 公益社団法人 土木学会 2017年10月 [査読有り][通常論文]
     
    昨今の沿岸災害時では，長周期波と短周期波が重合することによりその被害を拡大させた可能性が指摘されている．本研究では断面二次元水槽を用いて長周期波と短周期波が重合する波動場を再現し，そのときに構造物に作用する波圧特性を分析することを研究の目的とする．実験ではゲート急開放により発生させた段波を長周期波，造波装置により発生させた波を短周期波として，それらが重合したときに構造物に作用する波圧を計測した．また画像解析に基づき重合場の水面形を推定し，それに基づく水理特性とともに波圧特性を分析した．その結果，重合場の波圧特性は短周期波による鉛直方向加速度の影響を大きく受けることがわかった．さらに，短周期波と段波の非線形干渉に伴う砕波位置の変化が構造物に作用する衝撃砕波圧を最大化させ，それが支配的になり得ることが示唆された．
  • 東崚太, 下園武範, 山中悠資
    土木学会論文集B2(海岸工学) 73 2 1483 - 1488 公益社団法人 土木学会 2017年10月 [査読有り][通常論文]
     
    津波波源の不確実性や堤防の減災効果の評価に向けて，高速に津波浸水範囲を評価可能な手法を開発した．旧来のレベル湛水法に潜り越流と戻り流れ状態の計算を付与すると同時に，海岸低平地のデータベースを予め作成することにより広域の沿岸地域に適用する枠組みを構築した．モデルの妥当性を検証するため，2011年東北地方太平洋沖地震のデータを用いて，岩手県沿岸の約40地域での浸水範囲を同時に求めて比較した．堤防の効果が大きい地域では実際の破堤を考慮していないため大きく過小評価となったが，それ以外の地域では結果は良好な一致を示した．また，堤防高を変えて浸水範囲を求めることで入力波や地形特性による堤防減災効果の違いを広域的に検討できることを示した．
  • Yusuke Yamanaka, Yuichiro Tanioka
    PURE AND APPLIED GEOPHYSICS 174 8 3275 - 3291 2017年08月 [査読有り][通常論文]
     
    Large sector collapses and landslides have the potential to cause significant disasters. Estimating the topography and conditions, such as volume, before the collapse is thus important for analyzing the behavior of moving collapsed material and hazard risks. This study considers three historical volcanic sector collapses in Japan that caused tsunamis: the collapses of the Komagatake Volcano in 1640, Oshima-Oshima Island in 1741, and Unzen-Mayuyama Volcano in 1792. Numerical simulations of the tsunamis generated by each event were first carried out based on assumed collapse scenarios. The primary objective of this study is to present conditions related to the topography before the events based on inverse models of the topography from those results and tsunami survey data. The Oshima-Oshima Tsunami, which is the subject of many previous studies, was first simulated to validate the model accuracy and evaluate how run-up heights changed during the simulation as the topographic conditions changed. The run-up height was especially sensitive to the collapsed volume and frictional acceleration affecting the collapsed material; however, the observed run-up heights could be reproduced with high accuracy using proper conditions of frictional acceleration for the scenarios, even if they were not exact. A minimum requirement for the collapsed volume to generate the observed run-up height was introduced and quantitatively evaluated using the results of numerical tsunami simulations. The minimum volumes of the collapses of the Komagatake and Unzen-Mayuyama volcanoes were estimated to be approximately 1.2 and 0.3 km(3), respectively.
  • 山中悠資, 佐藤愼司, 田島芳満, 下園武範
    土木学会論文集B2(海岸工学) 72 2 403 - 408 公益社団法人 土木学会 2016年11月 [査読有り][通常論文]
     
    南海トラフ巨大津波の来襲が想定される複数の沿岸域を対象として，津波のソリトン分裂が発生する可能性を分析した．まず本研究の対象地域群と2011年東北津波のソリトン分裂が確認された地域群の地形特性を比較し，地形特性からソリトン分裂が発生しやすい地域の抽出を試みた．次に，事前に作成した来襲津波及び地形特性に基づくソリトン分裂発生の判定図を，各地域に適用することによりその発生可能性を分析した．これらの分析により，尾鷲湾及び須崎湾ではソリトン分裂が発生する可能性が高く，田辺湾及び志布志湾ではそれが低いことがわかった．さらに，尾鷲湾及び須崎湾では，湾水振動による波高増幅によってソリトン分裂が発生する可能性が高いことがわかった．
  • 山崎明日香, 佐藤愼司, 山中悠資
    土木学会論文集B2(海岸工学) 72 1 71 - 82 公益社団法人 土木学会 2016年11月 [査読有り][通常論文]
     
    静岡県伊豆半島西海岸の戸田，土肥，松崎地区を対象として津波の氾濫計算を実施し，津波災害のリスクを分析した．三地区の現時点の津波災害リスクは，人的被害と建物被害の和として，1年間当たり1.8～2.3億円／年と推定された．避難率の向上と堤防建設によるリスク低減量を客観的に比較するとともに，今後50年間で浸水想定区域からの移転奨励施策を実施した場合の，リスク低減や適切な堤防高さに及ぼす影響などを定量的に議論した．これらにより，それぞれの沿岸地区で導入される各種津波対策の効果を具体的に相互評価するとともに，津波の発生頻度のみで決定されているレベル1津波高に対し，社会的に適切な津波対策を柔軟に策定するスキームを提案した．
  • 田口裕介, 田島芳満, 中村駿一郎, 山中悠資
    土木学会論文集B2(海岸工学) 71 2 1675 - 1680 Japan Society of Civil Engineers 2015年11月 [査読有り][通常論文]
     
    台風HaiyanによりSan Pedro湾では甚大な浸水被害が生じたが，被害は湾奥部だけにとどまらず，湾西側の沿岸部では湾口付近においても湾奥部とほぼ同等の浸水高が目撃された地点もあった．現地で得た証言によると，浸水氾濫は高波を伴い，浸水継続時間は比較的短かったことが報告されている．本研究では，特に湾口部近傍でも高かった浸水高に着目し，数値解析および室内実験を通じてその特性を検証することを目的とする．数値解析では，高潮と高波の関係を調べ，湾口部では強い循環流と高波が複雑に重合していたことを明らかにし，室内実験では，段波と短周期波が重合する場を再現し，非定常流れと高波の重合による氾濫域での外力場の増大メカニズムを検証した．最後に得られた知見に基づきSan Pedro湾口部における浸水特性のメカニズムを考察した．
  • 大熊将平, 佐藤愼司, 山中悠資, 佐貫宏
    土木学会論文集B2(海岸工学) 71 1 58 - 68 Japan Society of Civil Engineers 2015年10月 [査読有り][通常論文]
     
    2011年3月11日に発生した東北地方太平洋沖地震津波による福島県の被害に関して，現地調査及び数値シミュレーションを行い，海岸構造物の破壊機構を解明した．また，構造物へ大きな波力を及ぼす段波に関する水理実験を行い，津波の波面勾配が限界値を超えると段波が発生し，その限界値は海岸の地形勾配が緩やかなほど小さくなることが分かった．また，段波が構造物に作用する衝撃波圧は，入射波前面の波面勾配が大きくなるほど大きくなることが確認された．実験結果を津波の数値計算と組み合わせることで，福島県沿岸域の段波発生を分析した．その結果，中部では最大水位が高くかつ激しい段波が発生した可能性が高いことがわかり，中部で特に卓越する海食崖地形が，波面勾配の急峻化と段波の発生に影響しているものと推察された．
  • Tsunami sediment analysis based on luminescence measurement
    Shinji Sato, Kanto Nishiguchi, Yusuke Yamanaka
    Proceeding of Coastal Sediments 2015年05月 [査読有り][通常論文]
  • 山中悠資, 佐藤愼司, 田島芳満
    土木学会論文集B2(海岸工学) 70 2 201 - 205 Japan Society of Civil Engineers 2014年11月 [査読有り][通常論文]
     
    This study aims at the estimation of tsunami wave force due to the 2011 Tohoku earthquake tsunami. Field survey in Ryori, Iwate Prefecture, suggested multiple mechanisms for the collapse of 8.6 m high coastal dikes. Numerical tsunami simulation based on the nonlinear dispersive wave theory revealed the concentration of tsunami-induced flow to the northern area which is considered to develop severe scour of the foundation. The model also simulated the large wave force was exerted to the dike due to the tsunami overflow as well as the impulsive breaker force due to 10m high short period wave generated at the wave front. The estimated wave force was consistent with the collapse of the parapet observed in the field study.
  • 山中悠資, 佐藤愼司, 田島芳満, 下園武範, 佐貫宏
    土木学会論文集B2(海岸工学) 70 2 206 - 210 Japan Society of Civil Engineers 2014年11月 [査読有り][通常論文]
     
    A fast tsunami simulation system was developed which utilized the superposition of point source computations stocked as a database. The single point source was represented by the Gaussian distribution with s=5 km. The propagation of the point source was computed by using the linear Boussinesq theory. The accuracy of the model was discussed in representing the actual tsunami source profile as well as in the dispersive tsunami propagation. The system was applied to a hypothetical Japan Sea tsunami used in the disaster mitigation planning of Tottori Prefecture. The system successfully displayed the sensitivity of local tsunami height to the tsunami source location and thus demonstrated the performance to assist specific evacuation planning in individual towns and cities.
  • 西口幹人, 佐藤愼司, 山中悠資, 竹森涼
    土木学会論文集B2(海岸工学) 70 2 291 - 295 Japan Society of Civil Engineers 2014年11月 [査読有り][通常論文]
     
    Luminescence measurements of coastal sand particles were applied to the analysis of paleo tsunami generated by a Japan Sea earthquake in 1833. Long-term coastal morphology was described for a 20 km sandy beach formed by fluvial sediments supplied from the Hinogawa River. The alongshore distribution of the thermo-luminescence of beach sand and the comparison of shoreline in old maps indicated historical beach erosion at old river mouth and westward longshore sand transport. The vertical distribution of the optically-stimulated-luminescence of a sediment core sampled 420 m inland from the present shoreline suggested coastal and aeolian accretion processes interrupted by a 7 cm thick tsunami sediment layer. Numerical tsunami simulation supported the movement of beach sand due to flooding tsunami.
  • Sensitivity Analysis of Damages around Katsushika Ward, Tokyo, Dependent on Locations of Levee Breach along the Arakawa River
    Yusuke Yamanaka, Nanae Kita, Yoshimitsu Tajima, Takaaki Kato
    Proceeding of International Alliance for Sustainable Urbanization and Regeneration 95 - 102 2014年10月 [査読有り][通常論文]
  • 山中悠資, 佐藤愼司, 田島芳満
    土木学会論文集B2(海岸工学) 69 2 171 - 175 2013年11月 [査読有り][通常論文]
  • 西口幹人, 劉海江, 佐藤愼司, 田島芳満, 山中悠資
    土木学会論文集B2(海岸工学) 69 2 291 - 295 土木学会 2013年11月 [査読有り][通常論文]
  • Dynamic behaviors of the 2011 Tohoku Tsunami in Ryori bay
    Yusuke Yamanaka, Yoshimitsu Tajima, Shinji Sato, Haijiang Liu
    Proceeding of Coastal Dynamics 1937 - 1946 2013年06月 [査読有り][通常論文]
  • 山中悠資, 田島芳満, 佐藤愼司
    土木学会論文集B2(海岸工学) 68 2 341 - 345 2012年11月 [査読有り][通常論文]
  • 袰川龍一, 高川智博, 佐藤愼司, 長坂陽介, 山中悠資
    土木学会論文集B2(海岸工学) 68 2 491 - 495 公益社団法人 土木学会 2012年11月 [査読有り][通常論文]
     
    Gravel movement on sand-gravel mixed beaches was investigated by using RFID technique which detects individual gravel tagged with a passive IC tag. At the same time, variation of the foreshore beach topography was recorded by RTK-GPS. Gravel movement mechanism and the corresponding beach face change were studied on the basis of seven field surveys performed in the period from January to February 2012. On the target beach, storm waves tended to transport many gravels onshore and develop a steep beach face. In contrast, downwash motion by moderate waves moved gravels offshore although a small amount of gravels was exchanged across the shoreline simultaneously. The movement of gravels on the foreshore appeared to be influenced by the presence of submerged breakwaters.
  • 長坂陽介, HarryYEH, 中尾秀之, 佐藤愼司, 田島芳満, 山中悠資
    土木学会論文集B2(海岸工学) 68 2 1331 - 1335 土木学会 2012年11月 [査読有り][通常論文]
  • Cohherency of quality factor of subsurface ground identified using vertical array records of earthquake motions
    Osamu Tsujihara, Yusuke Yamanaka
    Proceeding of 9th U.S. National and 10th Canadian Conference on Earthquake Engineering No.838 2010年07月 [査読有り][通常論文]
  • 辻原治, 山中悠資
    土木学会論文集A1(構造・地震工学) 65 1 195 - 201 Japan Society of Civil Engineers 2009年 [査読有り][通常論文]
     
    地盤震動の鉛直アレー観測が実施されるようになり，これらを用いた地盤同定が行われるようになった．これまでに，いくつかの方法が提案されており， S波速度の構造を推定することについては成果を上げているものの，減衰特性値の推定については，その精度向上が課題となっている．本研究は，Q値（減衰特性値）の感度を利用し，周波数ごとにQ値を同定するスイープ法に基づき，より明瞭な情報が抽出できるように手法を改良した．そして，KiK-net観測網の同一地点について，いくつかの異なる地震の際に得られた地盤震動記録から減衰特性の推定値の整合性について議論した．

受賞

  • 2023年02月 Earth, Planets and Space Highlighted Papers 2022
     
    受賞者: Yuichiro Tanioka;Yusuke Yamanaka;Tatsuya NakagakiCharacteristics of the deep sea tsunami excited offshore Japan due to the air wave from the 2022 Tonga eruption
  • 2022年11月 Coastal Engineering Committee, JSCE Coastal Engineering Journal Reviewer Award 2021
     
    受賞者: Yusuke Yamanaka

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業 若手研究
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 山中 悠資
     
    本研究は、水槽実験と数値実験の結果に基づき、沿岸域において観測される津波波形を用いた波源推定技術を高度化させることを研究の目的としている。 本年度は主に水槽実験を行い、定量的な計測データを蓄積した。水槽実験では断面二次元水槽を用い、水槽内に設置したゲートの急開(ダムブレイク)により津波を想定した段波を発生させることができる。波高や波形勾配が異なる様々な段波を発生させ、その水位変動および伝播過程を計測した。このようにして得られた実験結果に対して数値計算に基づく再現計算を行った。発生させた段波は水槽内の初期水深条件などに応じて様々な形態に遷移しながら伝播するが、その再現に適した数値モデルを選択して用いることで、実験結果を数値計算により比較的良好に再現できることを確認した。 1906年にコロンビア沖で発生した地震津波の波源を、沿岸域で観測されたその津波波形に基づき推定した。その推定波源をスケーリングしながら様々な規模の波源を仮想的に想定し、それらの伝播を二つの異なる数値モデル(線形長波モデルおよび非線形長波モデル)に基づき推定した。これらの結果に基づき、沿岸域で観測されることが期待される波形を両モデルから推定したところ、津波による水位上昇量が大きくなるほど期待される波形のズレが大きくなった。これは津波の非線形性の考慮の有無により生じる結果である。また沿岸域で数十cm程度の比較的小規模の津波でも、得られる波形は数値モデルによって異なることが確認された。この結果、観測津波波形に基づく波源推定において、津波の非線形性の影響を評価することの重要性が示された。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 下園 武範, 山中 悠資
     
    広域の沿岸低平地群の浸水被害を一括して効率的に評価できる浸水予測手法の構築に向けて，前年度に構築した基本モデルの検証・改良を行った．モデルは，海岸低平地を小領域のネットワークとして表現し，長波方程式に基づいて小領域間の質量・運動量交換を解いて浸水過程を再現する．このモデルでは，海岸地形を標高によって小領域に分割・整理した地形データベースを参照し，対象地域を小領域ネットワークとして表現した上で，海域の水位を境界条件として浸水計算を行うため，効果的な領域分割が精度および効率面で鍵となる．いくつかの理想化された地形条件の下で，非線形長波モデルに基づく詳細な浸水モデルによる結果との比較を通して，精度と計算コストの面から効果的な領域分割法を考案した．また，効率的かつ安定的にネットワーク計算を行うためのアルゴリズムについても改良を行った．様々な地形条件で精度検証を行った結果，ネットワーク型浸水モデルは従来の簡易浸水計算法では再現できなかった遡上や窪地や微高地などの存在する地形での浸水過程の再現も可能であることが確認できた．2011年東北地方太平洋沖地震津波のケースにモデルを適用した結果， 非線形長波方程式による浸水計算結果と比較して，より少ない計算単位数で同程度の精度で陸域の浸水を評価できることが確認された．また，地形情報データベースに人口メッシュデータを統合し，浸水計算結果から被害情報を算出できるようにモデルおよびデータベースの拡張を行った．
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 佐藤 愼司, 田島 芳満, 山中 悠資, 下園 武範
     
    砂礫海岸のトレンチ調査を実施し，侵食されにくい海浜の構造を考究した．宮崎海岸，高知海岸仁淀川流砂系，高知海岸物部川流砂系の3か所で調査を実施した．これらにより，海岸の侵食が，台風などの影響を受けて長期的に進行することが明らかになるとともに，海岸保全施設である離岸堤による土砂の捕捉が来襲波の波向きの影響を受けた地形変化を繰り返しながら20年以上継続すること，深さ約1m程度の深部には埋没カスプを含んだ礫層が卓越することなどが明らかとなった．来襲波浪エネルギーの大きい時期には標高2m程度の礫層上部まで侵食されるが，礫層の完全な侵食までには至らないなど，侵食に強い海浜の三次元構造が明らかとなった．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2015年04月 -2019年03月 
    代表者 : 谷岡 勇市郎, 高清水 康博, 西村 裕一, 菅原 大助, 伊尾木 圭衣, 山中 悠資
     
    沿海州の様々な場所にて津波堆積物調査を実施し津波イベントを認定し、さらにイベントの年代を推定した。12世紀ごろの津波について、北海道沿岸の津波堆積物を説明できる断層モデルを津波数値計算により推定した。トータルの断層長さは109㎞で北側の50㎞の断層で18mのすべり量が必要であることを明らかにした。これまでの仮定（６ｍ）を大きく超えることが明らかになった。12世紀の断層モデルは、1993年北海道南西沖地震の断層モデルと1983年日本海中部地震の断層モデルにちょうど挟まれる形となっていることが明らかになった。また、1741年渡島大島の火山噴火に伴う山体崩壊による津波を数値計算により再現した。
  • 日本学術振興会：科学研究費助成事業 特別研究員奨励費
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 山中 悠資
     
    本年度は日本海域で想定されている地震津波断層を用いて、沿岸域で予想される津波挙動を詳細に分析した。まず、複数の断層による連動型地震が想定されている断層を対象として、それにより形成される津波の伝播計算を行った。次にその構成断層各々が単独で地震を発生させる場合を想定し、同様にそれによる津波の伝播計算を行った。一般的には連動地震の方が地震規模が大きくなり、形成される津波規模も大きくなるが、これらの伝播計算結果の比較から、沿岸域においては単独地震による津波の方が連動地震による津波よりも局所的に津波高が大きくなる場合があることがわかった。 上述の結果から、各沿岸域単位で予想される津波挙動を分析する必要があることがわかったため、鳥取県及び島根県に位置する美保湾を分析対象としてさらに詳細な分析を実施した。まず上述の分析と同様に想定されている地震津波断層を用いて津波の伝播計算を行い、美保湾における津波の挙動を推定した。その結果、特に日本海東縁部及び北海道周辺海域で形成された津波においては、美保湾では第一波目ではなく後続波で津波高が最大になる傾向があることがわかった。さらに、沿岸部固有振動によってその後続波が大きくなっている可能性があることがわかった。これを踏まえて、美保湾で励起されやすい津波の振動成分の推定及び、それと各津波断層が形成しやすい津波の振動成分の比較を行った。その結果、美保湾に影響が大きかった地震津波断層が励起しやすい津波の振動成分と湾内で見られたその振動成分が整合的であることがわかった。したがって、本研究の手法を用いることにより、各地震津波断層が各沿岸域で形成しやすい津波特性を予察的に推定することが可能であることがわかった。
  • 日本学術振興会：科学研究費助成事業 特別研究員奨励費
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 山中 悠資
     
    前年度までの研究により，2011年東北津波が来襲した岩手県綾里湾では波の分裂現象(ソリトン分裂)が生じていたことや，それが綾里湾の海岸堤防の破壊に寄与した可能性などが明らかになっている．このように，津波のソリトン分裂は沿岸構造物の破壊に影響を与えることや氾濫域を拡大させることがあるため，その発生可能性を考慮しながら津波防災計画を策定する必要があると考えられる．防災計画策定の際には数値計算を行い，津波の伝播・氾濫を予測するが，その発生を考慮した詳細な数値計算は計算負荷が非常に大きくなる．そこで，まずソリトン分裂の発生を考慮した数値実験を行ってそれが発生する津波及び地形条件を抽出した．それに基づき，ソリトン分裂発生の判定図を作成した．実際にソリトン分裂が発生した地域を対象としてその判定図を2011年東北津波に適用し，詳細な数値計算を行わなくてもその発生を予測できることを確認した．この手法を現在想定されている南海トラフ巨大地震津波に適用し，ソリトン分裂が発生する可能性がある地域を示した． 適切な防災計画を策定するためには，各地域に来襲する津波波形を事前に精度良く把握しておく必要がある．しかしながら，数多くの想定津波を対象にしながら各地域に来襲する津波波形をそれぞれ把握することは，計算負荷の観点からも非効率的である．そこで，前年度に構築した，日本海津波を対象とした津波計算システムに基づき，沖合任意地点における津波波形を高速に計算することができるウェブサイトを開設した．同サイトでは日本海東縁部を波源とする任意津波の波形を計算することができる．これを活用することで，日本海沿岸域の防災計画の策定を効率的に行うことができる．

大学運営

委員歴

  • 2022年06月 - 現在   土木学会   環境賞選考委員会幹事
  • 2022年04月 - 2024年03月   日本地震学会   「地震」編集委員会委員

Copyright © MEDIA FUSION Co.,Ltd. All rights reserved.