Shibayama, Atsushi (Central Research Institute of Electric Power Industry) | Miyagawa, Yoshinori (Central Research Institute of Electric Power Industry) | Kihara, Naoto (Central Research Institute of Electric Power Industry) | Kaida, Hideki (Central Research Institute of Electric Power Industry)
The damages of the gigantic tsunami that followed the 2011 Great East Japan Earthquake were confirmed on reinforced concrete (RC) structures (Nandasena et al., 2012). Moreover, the damages caused by the tsunami debris collision were confirmed in addition to the damages caused by only the tsunami. Therefore, it is important to clarify the response characteristics of the structure subjected to the tsunami wave force and collision force, and to establish a response evaluation method by numerical analysis. However, the response characteristics of RC structures subjected to two external forces with significantly different timings of actions--namely, wave pressure and collision forces--have not been clarified. Furthermore, to assess the responses of RC structures using numerical analysis, the two different types of superimposing external forces must be considered. However, the applicability of numerical analysis under such external force conditions has not been sufficiently verified. In this research, a large-scale debris collision experiment was first conducted to experimentally investigate the response of an RC vertical wall subjected to the wave pressure and debris collision forces. Next, a reproducibility analysis of the experiment was performed with nonlinear finite element analysis to examine the adaptability of the finite element analysis.
A physical wave maker system is established to generate the undular bores by superimposing successive solitary waves on the surge wave. The successive solitary waves are generated by the long-stroke piston wavemaker, and the surge wave is generated by a special valve-pump system. The valve-pump system is proved to produce the surge wave precisely and delicately. The superimposition appears that the solitary waves ride on the surge wave. The surge wave acts as the deeper water for the solitary wave to propagate, which affects the amplitude of solitary waves. In the present study, two successive solitary waves can be generated and superimposed on the surge wave, and the experimental data show good repeatability. A profile of the undular bores simulated by numerical computation is well reproduced in the basin.
Tsunami is one of the devastating natural hazards, which may cause thousands of fatalities and millions of property loss. Many numerical studies (Behrens and Dias, 2015) on the tsunami have frequently been reported in recent years, which greatly contribute to the understanding on the propagation mechanism of the tsunami and protection to the coastal structures. However, the computational cost and the complex topographies hinder the numerical simulation especially in the modelling of offshore and onshore processes. The physical model experiment is a good choice to study the mechanism of tsunamis in this region, such as the evolution and propagation with the sediment transport, and the inundation and the impact on the onshore structures.
The first question of the physical experiment for tsunami problem is how to generate the tsunami-like wave in the laboratory. As a simplification, the solitary wave generated by the wavemaker is widely used to mimic tsunami wave. Concerning the generation of solitary wave, Goring (1978) specified the movement of wavemaker plate to generate solitary waves, which was advanced by Malek-Mohammadi and Testik (2010). They took into account the unsteady nature of the solitary wave generation process. Xuan et al. (2013) studied the generation of two successive solitary waves of different amplitude. Although the piston-type wavemaker is doubted to satisfy the wavelengths and periods of the tsunami and the stable trough-led wave shape, many valuable achievements are still obtained by this simplification.
This thesis investigates the collision force of driftwoods and small boats due to tsunamis. Even though there are some calculation formulas from past experiments, quantitative approaches for design criteria of tsunami protection structures are not established. Accordingly, to upgrade design criteria of tsunami protection structures, the thesis aimed to investigate into an adaptability of the formulas obtained past researches and new experimental evaluation formula derived from present research comparing with the measurements of hydraulic model experiment.
On March 11, 2011, Tohoku - Pacific Coast Earthquake tsunami struck a large area on the Pacific coast, especially from Chiba Prefecture to the coastal areas of Aomori Prefecture, where the damage to coastal structures was so great, not only port facilities, but also shore protection facilities such as breakwater, seawall, and sea embankment. In particular, the area around the Fukushima Daiichi nuclear power plant suffered from the damage generated by radiation leak due to tsunamis.
On the other hand, it was confirmed that the Kamaishi bay-mouth breakwater delayed reaching tsunami in the bay and had the effect of reducing the tsunami height. In the shore protective facilities such as breakwater, it is considered to have protective effect on the tsunami(Hiraishi et al., 2011). Accordingly, it is necessary to make the shore protective facilities tenacious structure that can withstand the port structure without collapsing even for the largest scale tsunami.
In this way, this report investigates the collision force of driftwoods and small boats due to tsunamis. Even though there are some calculation formulas from previous researches, quantitative approaches for design criteria of tsunami protection structures are not established. Accordingly, to upgrade design criteria of tsunami protection structures, the research aimed to investigate into an adaptability of the formulas from previous researches and new experimental evaluation formula derived from present research.
In this paper, to compare the measurements with the calculation formula, we have a hydraulic model experiment. With regard to small boat, we use the measurements of experiment conducted in 2017 and of similar experiments conducted in 2016(Okura, 2017) and 2015(Ono and Hiraishi, 2017) as well in this experiment. In contrast, with regard to driftwood, we use the measurements of similar experiments conducted in 2016 and 2015.
There has been an increasing number of studies on the tsunami hazards in the South China Sea region since the 2004 Sumatra earthquake. Many of them are carried out based on tsunami scenario simulations, which adopt seismic source models constructed from scaling relations between seismic magnitude/momentum and rupture parameters. Various sets of scaling relations have been proposed on the basis of different earthquake catalogues. In this study, we perform synthetic tests to evaluate the impact of scaling relations on the generation and propagation tsunami waves in the South China Sea. Results show that the range of the affected coastline can be significantly different for an earthquake of the same magnitude using different scaling relations. Additionally, the maximum tsunami wave height near major cities may vary as large as two times. Thus, it is worth further research on the choice of scaling relations for tsunami hazards assessment and the building of early tsunami warning system.
The Manila subduction zone was identified (Kirby et al., 2006) as having high potentials to generate hazardous tsunamis in the USGS (the United States Geological Survey) tsunami source workshop (Liu et al., 2007). As shown in Fig. 1, seismic events are very active near the Manila Trench. Tsunami from the Manila Trench is a potential threat to coastal countries around the South China Sea (SCS), such as China, Vietnam, Philippines et al. Although studies on tsunami scenarios have been performed (Liu et al.2007, 2009; Wu & Huang, 2009, Megawati et al., 2009, Nguyen et al., 2014), the rupture model and mechanism of the Manila trench is far away from being enough.
Eyes were turned to the Manila subduction zone after the 2004 Sumatra tsunami. Basic geometry and orientation parameters were provided by Kirby et al.(2006). But the parameters cannot be employed directly to performing numerical simulations, for the rupture width, the focal depth and the dislocation were not provided. Liu et al.(2007, 2009) provided the source parameters of an earthquake scenario Mw8.0 based on the geometry and orientation parameters of Kirby et al.(2006). The rupture width was identified as 35 km by squaring the region of an earthquake Mw7.3 and its aftershocks in 1999. The dislocation was calculated from the scaling relation of Wells & Coppermith (1994). However, the slip of the sub-fault E6 is the largest among the six sub-faults, which conflicts with geodetic data (Li et al., 2016). Based on geodetic data from Yu et al.(1999), a complex rupture model was provided by Megawati et al.(2009) by splitting the Manila fault into 33 pieces of elements. An earthquake, whose moment magnitude reaches Mw9.4, is probably to dilacerate the whole Manila Trench and brings extreme tsunami. Wu & Huang (2009) also provided a rupture model of an earthquake Mw9.35 by simply comparing the geometric similarity of the Manila fault to the fault of 1960 Chilean earthquake, the 1964 Alaska earthquake, and the 2004 Sumatra earthquake. Nguyen et al.(2014) redesigned the subfaults' geometry and orientation parameters. In fact, except the geometry and orientation parameters of the Manila Trench that proposed by Megawati et al.(2009), the rest models of earthquake source parameters do not meet the scaling relations (SRs) of megathrust fault. Apart from providing all parameters of an earthquake source, they also studied the tsunami impact on the eastern coast of Vietnam (Nguyen et al., 2014), Singapore (Huang et al., 2009) and Taiwan (Wu & Huang, 2009). Liu et al.(2007, 2009) attempted to establish an early tsunami warning system in the SCS so as to mitigate disasters to coastal land areas around the SCS.
The main purpose of this study is to investigate tsunami-induced loading on coastal structures and the influences of mitigation walls in reducing tsunami forces by using smoothed particle hydrodynamics method. Numerical simulations were built to examine the force reduction effect of mitigation walls with different locations, heights and inclinations. The results show that mitigation wall with larger height and further distance can effectively reduce the tsunami forces. Additionally, mitigation wall with inclined angle (e.g. 45°) is helpful to reduce and stabilize the tsunami forces.
In recent decades, several major tsunamis have caused severe damages both on human lives and coastal structures. The 2004 Indian Ocean tsunami is the deadliest disaster with more than 300,000 people losing their life and approximately 1.5 million people displacing from their homes (Ghobarah et al., 2006). The 2011 Japan tsunami caused about 20,000 casualties and more than 676,000 damaged houses and buildings (Suppasri et al.,2012). The Japanese Cabinet Office estimated direct losses of more than $300 billion, making it the costliest natural disaster on record. Post-disaster surveys have found that some structures previously understood to be invulnerable to tsunamis were heavily damaged or even destroyed during such events (Nistor et al., 2005; Yeh et al., 2013). In addition to these observations, an extensive literature review on current tsunami design documents indicated that hydrodynamic loading during tsunami inundation is not properly considered during the design of nearshore structures (Nistor et al., 2009).
In addition to field surveys, a number of laboratory experiments have been conducted to study tsunami impact on structures, and this study briefly reviews some of them. Chanson (2006) analyzed visual images of an actual tsunami bore resulting from the 2004 Indian Ocean tsunami and demonstrated that the flow characteristics of the bore were very similar to those of a dam-break wave. By using dam-break wave approach, Árnason et al. (2009) studied the interaction of bores propagating on a wet bed with surface-piercing structures of various cross-sections. Nouri et al. (2010) conducted an experimental test program to study the influence of tsunami bores in laboratory in terms of the exerted force and pressure on the structure. A good agreement was observed with the results of similar experiments available in the literature at the time. Al-Faesly et al. (2012) conduct a comprehensive experimental program on structural models subjected to simulated hydraulic bores, the variables in this test program included: cross-sectional shape of the structural models, bore depth, effect of initial flume-bed surface conditions, and damping effect of mitigation walls on hydraulic bores. Rahman et al. (2014) conducted an experimental study to investigate the force reduction effects of seawalls on onshore structures. He focused on two parameters, including the location and height of the wall, to determine their effect on the generated force. Based on his findings, he concluded that seawalls located close to the coastal structure with adequate height are capable of significantly reducing the exerted base shear force.
Beach morphology is one of the major controlling factor of wave interactions with land. We address here its impact on tsunamis based on two recent destructive events (2004 Indian Ocean tsunami and 2011 great East Japan tsunami). This investigation uses numerical recreation of these events to understand the behavior of tsunami in front of different beach morphological features. Particular focus is given on tsunami interaction on partially closed bays and associated headlands as comparatively higher energy dissipation is observed at bays in both events. In addition, it was confirmed the above behavior by subjecting an artificial, common bathymetry with an ideal coastline with a tsunami strike. These results confirmed that tsunamis behave in an opposite manner when they interact with bays and headlands compared to wind generated short period waves.
A Tsunami is a series of ocean waves that often occur due to submarine earthquakes. Gigantic waves are created sending surges of water, sometimes reaching heights of over 30 meters on to land. These wave trains can cause widespread destruction within a very short time frame when they strike the shore. Once generated, tsunamis race across the sea of up to 800 km/h where their long wavelengths mean they lose very little energy along the way. Once the tsunami strikes land, it can run up to several miles on a flat land or an unprotected beach until it dissipates its energy.
Focus and Objectives
When a tsunami strikes, the damage it would cause is not only depend on wave energy but also on morphological features of the coastline. Disasters that have occurred in recent times has left important evidences that proves the above fact as some affected areas were totally destroyed while others showed very less damage. The energy dissipation of tsunami and wind waves is different due to the characteristics of the two kinds of waves. A tsunami is a shallow water wave, even in Deep Ocean, with very long wavelength and relatively high especially near shore. It does not break when attacking the shore rather composed of run-up and run-down (Pal, 2010). From this observation and considering the coastal morphology directly governs wind wave energy dissipation. It can be suggested that the role of beach morphology in a tsunami event is different from that of the behavior of an ahead of wind waves. Therefore, having an idea on this nature is important. The primary aim of the study is to identify the common morphological features of coastal areas of which a tsunami will have a destructive impact. A numerical model simulating the 2004 and 2011 events has achieved the objectives of this study.
Design standards of vertical evacuation buildings against tsunami loads have been developed in Japan and the USA. In this paper, we compare the overall tsunami loads and structural design requirements of the two standards. Hydrodynamic forces from each standard are further compared for example cases, and it is found that for a given inundation depth, the standard in Japan generally requires higher capacity for vertical evacuation buildings than in the USA. The USA standard explicitly requires a 2,500-year Maximum Considered Tsunami design hazard. In Japan, it is expected that the local governments will determine a worst case deterministic scenario for their region, and the design return period for the maximum considered tsunami is not specified.
The purpose of this paper is to provide an overview of the technical methodology utilized in Japan and the United States of America for the tsunami-resilient design of vertical evacuation buildings. Taller structures in a community can provide effective secondary alternative refuge when evacuation out of the inundation zone is not possible or practically achievable for the entire population. During the 2011 Tohoku Tsunami in Japan, many taller buildings were successfully used as evacuation buildings saving tens of thousands of lives (Fraser et al., 2012). To design and construct buildings resistant to tsunami loads, quantitative evaluation of tsunami inundation and loads applicable to structural design is essential. The tsunami evacuation building also needs to reach sufficient elevation such that the refuge areas are located well above the tsunami water elevation considering possible splash-up during tsunami inundation and the inherent uncertainty in estimating tsunami run-up elevations.
Design guidelines for tsunami evacuation buildings in Japan were developed by a task committee under the Japanese Cabinet Office in 2005 (JCO, 2005) referring to “Structural Design Method of Building to Tsunami” (Okada et al., 2004) which introduced a formula to compute tsunami loads expected to act on buildings constructed at the coastlines. In November 2011, The Housing Bureau of the Ministry of Land, Infrastructure and Transport issued updated Interim Guidelines on the Structural Design of Tsunami Evacuation Buildings (MLIT, 2011), after considering new findings of the Great East Japan Earthquake of March 11, 2011. In February 2015, a chapter on tsunami loads was established in “AIJ (Architectural Institute of Japan) Recommendations for Loads on Buildings” as the outcome of the Tsunami Loads Subcommittee under the Committee for Loads on Buildings in AIJ (AIJ, 2015).
Tsunamis cause tremendous damages and loss of life at many coastal areas around the world. The main purpose of this study is to investigate propagation of tsunami in order to validate tsunami run-up and inundation and assess ocean environment at shallow water region. We used Smoothed Particle Hydrodynamics based on Shallow Water Equation (SWE-SPH) to reproduce the previous tsunami event. The results were compared with water elevations at the survey locations. Moreover, we applied to compute wave propagation and velocity filed around offshore structures such as a wind farm.
Tsunamis cause tremendous damages and loss of life at many coastal areas around the world. Tsunamis with destruction at spreading areas should be accurately predicted to establish evacuation routes and to find out safety locations at inundation areas. Tsunami inundation process at flooding area and tsunami behaviors become a key factor to protect coastal areas and to reduce number of victims. In particular, it is difficult to estimate wave deformation and its propagation at shallow water region caused by shoring due to bottom topography and coastline.
In general, wave propagation at shallow water region can be represented by Sallow Water Equations (SWE) and its computation is lower cost comparing with that of full-3D model. In Grid Based Method, to obtain reliable results dynamically, adaptive structured (Liang, 2009; George, 2010) or unstructured grid systems (LeVeque, 2007) were employed. However, the Grid Based Method needs to generate grids at complicated domains, and then it is difficult to compute water elevation and wave propagation at focused areas. On the other hand, in Particle Based Method, Rodriguez-Paz and Bonet (2005) introduced a shallow water formulation based on SPH method (Monaghan (1994)) with variable smoothing length, which treats the continuum as a Hamiltonian system of particles. And also, de Leffe et al. (2010) employed Riemann approach proposed by Vila (1999) to realize more robustness for computations. Moreover, R. Vacondio et al. (2012a) applied open boundaries conditions using SWE-SPH for shallow water flow to simulate flood inundations due to tsunami attacking.
In this paper, we conducted study of tsunami inundation forecasting in Aichi and Mie Prefecture, Japan. In this study, a database that consists of precomputed tsunami inundation and waveform from multiple scenarios is developed. This method is divided into two stages. In first stage, preliminary earthquake information is used to find appropriate tsunami inundation scenario in database. In second stage, a real-time tsunami waveform simulation is conducted to find best scenario by comparing computed tsunami waveforms and those in database. Furthermore, this method can produce good tsunami inundation forecast in a reliable time.
The 2011 Tohoku earthquake caused more than 15,000 people died and missing (Kazama and Noda, 2012). About 3 min after the earthquake, Japan Meteorological Agency (JMA) announced tsunami warning and advisories for along the coast of Hokkaido to Kyushu and the Ogasawara Islands (Ozaki, 2011). To calculate and determine earthquake hypocenter coordinate and magnitude, JMA utilizes real-time seismic data. By using this system, earthquake information can be obtained shortly after earthquake, but the system underestimated magnitude of the 2011 Tohoku earthquake (Gusman and Tanioka, 2015). JMA estimated initial earthquake magnitude was Mjma 7.9 obtained within 3 min after earthquake. Then, it is revised to be Mjma 8.4 in more than 1 h after earthquake (Ohta et al., 2012). Further study revealed that those magnitudes underestimate actual earthquake magnitude Mw 9.0 (e.g. Gusman et al., 2012; Satake et al., 2013).
The future Nankai Trough earthquake is expected to be occurred in the near future and more destructive than the 2011 Tohoku earthquake. Ishibashi (2004) explained that great earthquake has recurrence interval of 100-200 years based on historical records. Compared to the other earthquake zones in Japan, the Nankai Trough located very near to the coast (less than 150 km) (Mulia et al, 2017). If an earthquake followed by tsunami occurred, tsunami wave would require short time to reach the coast. The 1944 Tonankai and the 1946 Nankai earthquake are the last two earthquakes in Nankai Trough zone followed by tsunami that causing severe damages in southeast of Japan. The estimated seismic moment of the 1944 Tonankai earthquake is 2.06 × 1021 Nm (Mw 8.1) (Baba et al., 2006). This earthquake generated large tsunami with maximum inundation up to 2.8 m as observed in Owase city during field survey (Hatori et al., 1981). The 1946 Nankai earthquake was a shallow earthquake (4.1 km hypocenter depth) with magnitude of Mjma 8.0. More than 11,000 and 1,500 houses were collapse and washed away, respectively by tsunami with maximum wave height of about 6 m (Murotani et al., 2015).
The paper describes the main features of the pipelined Tsunami Modeling Infrastructure supporting high-speed tsunami modeling on system with rather limited computational resources. The pipelining scheme is realized by distributing bathymetries over computational resources and synchronization of processing of each area using buffering of boundaries between areas. It also describes adopting this scheme to cloud-based computations allowing creating flexible and reconfiguring computational scheme with a variable set of modeling zones. Preliminary results of numerical modeling experiments are also presented.
The tsunami modeling can be considered as a heavy-computational problem requiring versatile approaches based on integration of them. The most known, accurate and widely used packages are TUNAMI described in Shuto et. al., (1995) and MOST presented in Titov, (1988) Titov, (1998), and Titov and Gonzalez, (1997). For obtaining results of the tsunami propagation, be more reliable (distribution of tsunami wave heights in a shelf zone), rather a small step of a computational grid (about tens meters) is necessary. If we simulate the tsunami propagation in the whole area including both a source zone and sites of the coast, we are interested in, using this small spatial grid step, then because of the stability condition we will be compelled to carry out calculation with a small time step. This will bring about a significant increase in the time of numerical calculation that is inadmissible in real-time calculations. Therefore it is necessary to carry out such calculations with the use of the computational grids whose spatial step decreases when approaching the coast.
This research is focused on designing a high-speed scheme for tsunami modeling used nested computing. The basis for this research is the original grid-switching algorithm modeling tsunami propagations described in Hayashi et. al., (2015). We have adopted the MOST package to a computational scheme in which tsunami wave parameters are transferred from a larger domain to the embedded smaller one by means of the boundary conditions. This allows decreasing the total amount of calculations by excluding unimportant coast areas from the calculation process.