Numerical Study on Tsunamis Excited by 2006 Pingtung Earthquake Doublet (original) (raw)
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A Revised Evaluation of Tsunami Hazards along the Chinese Coast in View of the Tohoku-Oki Earthquake
Pure and Applied Geophysics, 2012
Japan's 2011 Tohoku-Oki earthquake and the accompanying tsunami have reminded us of the potential tsunami hazards from the Manila and Ryukyu trenches to the South China and East China Seas. Statistics of historical seismic records from nearly the last 4 decades have shown that major earthquakes do not necessarily agree with the local Gutenberg-Richter relationship. The probability of a mega-earthquake may be higher than we have previously estimated. Furthermore, we noted that the percentages of tsunami-associated earthquakes are much higher in major events, and the earthquakes with magnitudes equal to or greater than 8.8 have all triggered tsunamis in the past approximately 100 years. We will emphasize the importance of a thorough study of possible tsunami scenarios for hazard mitigation. We focus on several hypothetical earthquake-induced tsunamis caused by M w 8.8 events along the Manila and Ryukyu trenches. We carried out numerical simulations based on shallow-water equations (SWE) to predict the tsunami dynamics in the South China and East China Seas. By analyzing the computed results we found that the height of the potential surge in China's coastal area caused by earthquakeinduced tsunamis may reach a couple of meters high. Our preliminary results show that tsunamis generated in the Manila and Ryukyu trenches could pose a significant threat to Chinese coastal cities such as Shanghai, Hong Kong and Macao. However, we did not find the highest tsunami wave at Taiwan, partially because it lies right on the extension of an assumed fault line. Furthermore, we put forward a multi-scale model with higher resolution, which enabled us to investigate the edge waves diffracted around Taiwan Island with a closer view.
Analysis of the tsunami generated by the 2007 Noto Hanto earthquake
Earth, Planets and Space, 2008
The 2007 Noto Hanto earthquake generated a small tsunami that was recorded at several tide gauge stations along the coast of the Japan Sea. The most important feature of this tsunami is that two waveforms recorded at the Wajima and Noto tide gauge stations, which are located 30 km apart, showed very different later phases-the large later phases recorded at Noto were not observed at Wajima. Numerical simulation of the tsunami indicated that the difference was caused by the shallow water bathymetry around the Noto peninsula. The large tsunami that was amplified at a few tens of kilometers off the north coast of the Noto peninsula propagated towards the Noto tide gauge station, but not towards the Wajima station. This study indicates that the propagation of a tsunami caused by a shallow earthquake beneath a coastal area is significantly affected by the local bathymetry. A comparison of the observed and computed tsunami waveforms indicated that the slip amount of the fault was 0.8 m. The seismic moment of the Noto Hanto earthquake was calculated to be 0.94 × 10 19 N m (M w 6.6).
Tsunami propagation scenarios in the South China Sea
Journal of Asian Earth Sciences, 2009
This paper studies extreme tsunami scenarios in the South China Sea potentially originated from a giant rupture along the Manila Trench. Tsunami height and arrival time to the major coasts along the SCS are computed using TUNAMI-N2-NUS model. Sensitivity of tsunami parameters to the rupture properties is explored numerically. For tsunami waves potentially originated from the Manila Trench, it is shown that the Sunda Shelf and the Natuna Islands may act as a natural barriers, sheltering southwest part of the South China Sea and Singapore Strait.
Tsunami hazards along Chinese coast from potential earthquakes in South China Sea
Physics of The Earth and Planetary Interiors, 2007
The pair of earthquakes off Taiwan on December 26, 2006 and the subsequent disruption of the Internet traffic have called attention to the potential destructive hazards along the Chinese coast from tsunamis. Historical records show past tsunami earthquakes in this region. Using GPS, earthquake focal mechanisms and geological evolution, we have delineated the dangerous zones in the Philippine Sea plate where major earthquakes may occur. The Manila Trench is identified as being most susceptible to future major earthquakes. We have obtained the local Gutenberg-Richter relationship for five sections along the Philippine Sea plate boundary and use this information for determining the probability distribution for tsunami waves of various heights to impinge on various Chinese cities. We devise a new method called the probabilistic forecast of tsunami hazard (PFTH), which determines this probability distribution by direct numerical simulation of the waves excited by hypothetical earthquakes in these zones. We have employed the linear shallow-water equations over the South China Sea. We have also compared them with results from the nonlinear version and found that the linear treatment serves our purpose sufficiently well. In the next century the probability of a wave with a height of over 2.0 m to hit near-coast ocean of Hong Kong and Macau is about 10%. Cities in Taiwan are less vulnerable than those on the mainland coast.
Tsunami Simulations for Regional Sources in the South China and Adjoining Seas
Pure and Applied Geophysics, 2011
We present 14 scenarios of potential tsunamis in the South China Sea and its adjoining basins, the Sulu and Sulawezi Seas. The sources consist of earthquake dislocations inspired by the the study of historical events, either recorded (since 1900) or described in historical documents going back to 1604. We consider worst-case scenarios, where the size of the earthquake is not limited by the largest known event, but merely by the dimension of the basin over which a coherent fault may propagate. While such scenarios are arguably improbable, they may not be impossible, and as such must be examined. For each scenario, we present a simulation of the tsunami's propagation in the marine basin, exclusive of its interaction with the coastline. Our results show that the South China, Sulu and Sulawezi Seas make up three largely independent basins where tsunamis generated in one basin do not leak into another. Similarly, the Sunda arc provides an efficient barrier to tsunamis originating in the Indian Ocean. Furthermore, the shallow continental shelves in the Java Sea, the Gulf of Thailand and the western part of the South China Sea significantly dampen the amplitude of the waves. The eastern shores of the Malay Peninsula are threatened only by the greatest-and most improbable-of our sources, a mega-earthquake rupturing all of the Luzon Trench. We also consider two models of underwater landslides (which can be triggered by smaller events, even in an intraplate setting). These sources, for which there is both historical and geological evidence, could pose a significant threat to all shorelines in the region, including the Malay Peninsula.
Acta Geotechnica, 2009
This paper discusses the applications of linear and nonlinear shallow water wave equations in practical tsunami simulations. We verify which hydrodynamic theory would be most appropriate for different ocean depths. The linear and nonlinear shallow water wave equations in describing tsunami wave propagation are compared for the China Sea. There is a critical zone between 400 and 500 m depth for employing linear and nonlinear models. Furthermore, the bottom frictional term exerts a noticeable influence on the propagation of the nonlinear waves in shallow water. We also apply different models based on these characteristics for forecasting potential seismogenic tsunamis along the Chinese coast. Our results indicate that tsunami waves can be modeled with linear theory with enough accuracy in South China Sea, but the nonlinear terms should not be neglected in the eastern China Sea region.
Simulation of Tsunami Propagation with Space-varying Seafloor Topography
2010
Tsunami is generated by a sudden deformation of the seafloor, such as uplift and subsidence, caused by fault motion of an earthquake below the seafloor. Numerical simulation of tsunami propagation is frequently used to predict the arrival time and the order of magnitude of the inundation for disaster mitigation purposes. In the propagation process, reflected waves are generated by the change in water depths and influence the tsunami height estimation, in particular in the later phases. In this study, we try to simulate tsunami propagation to accommodate the 2-D varying seafloor topography. In our simulation code, we assume water as a non-viscous fluid. A finite difference method (FDM) is employed using three equations; the equations of continuity, motion, and barotropy. In this study, we simulate the tsunami generation by a sudden change in the water depth and the propagation, using the Pearson approximation to accommodate the spatially varying water depth. We impose the seafloor topography on the basis of the 500m-mesh bathymetry data that JODC (Japan Oceanographic Data Center) provides. We assume a domain included in the data region and simulate tsunami. By using this method, we are able to calculate not only the propagation velocity due to the change in the water depth, but also reflected waves at the same time.
Applied Mathematical Modelling, 2011
The processes of tsunami evolution during its generation in search for possible amplification mechanisms resulting from unilateral spreading of the sea floor uplift is investigated. We study the nature of the tsunami build up and propagation during and after realistic curvilinear source models represented by a slowly uplift faulting and a spreading slip-fault model. The models are used to study the tsunami amplitude amplification as a function of the spreading velocity and rise time. Tsunami waveforms within the frame of the linearized shallow water theory for constant water depth are analyzed analytically by transform methods (Laplace in time and Fourier in space) for the movable source models. We analyzed the normalized peak amplitude as a function of the propagated uplift length, width and the average depth of the ocean along the propagation path.
A method for numerical modeling of tsunami run-up on the coast of an arbitrary profile
In this paper a new method for numerical simulation of the long wave run-up process is proposed. Nonlinear shallow water equations are used to describe wave propagation up to the water-edge point. Then a special algorithm is used to estimate flow parameters and location of the moving water-edge point. It is based on energy and mass conservation laws. Several series of one-dimensional computations were carried out. A shore profile, which gives the maximum run-up height for the fixed initial wave parameters, has been found. Results of modeling tsunami run-up on the real shore in the Akita prefecture (Japan) are presented.
Geophysical Journal International, 2009
The present study investigates the tsunami generation process by using 3-D numerical simulations and the linear potential theory. First, we evaluate the relation between sea-bottom elevation and sea-surface elevation as function of source size L, sea depth H and source duration T, based on 3-D numerical simulations. The surface elevation decreases with increasing sea depth and source duration. The difference between the sea-bottom and the sea-surface elevation appears when the source size is smaller than approximately 10 times the sea depth for a short source duration. The linear potential theory can precisely predict the numerical simulation results. Based on the theory, we can consider the tsunami generation as two spatial lowpass filter processes, in which the cutoff wavenumbers are given by the sea depth and the source duration. The criteria for small source size and short source duration are given as L < 13H and T < L/(8c), respectively, where c is the phase velocity of the tsunami. We then simulate the tsunami generation of the 1896 Sanriku tsunami earthquake, Japan. The simulated sea-surface elevation is significantly different from the sea-bottom elevation, which suggests the need for correction of the sea depth and source duration for the precise evaluation of the initial water-height distribution. To include these effects in 2-D simulations, we can use the impulse response function and add the fractional sea-surface uplift within the time step to the sea surface, for each time step.