Wave dispersion study for tsunami propagation in the Sea of Marmara

In this paper the aim is to investigate whether there are differences between the dispersion and non-dispersion solutions on tsunami propagation. For this purpose, two numerical models of tsunami propagation are compared. One of these numerical models is a nondispersive model that uses Saint Venant equations and the other is a dispersive model that uses Boussinesq equations. The tsunamis resulting from a submarine mass failure (SMF) which is settled at the bottom of the north eastern Sea of Marmara are examined. An analytical solution considering wave dispersion is developed for obtaining near-field tsunami amplitudes above the submarine mass failure. Numerical modeling is used at the sea surface from the common boundary called as liquid boundary with incident waves up to the coastal regions to get the tsunami amplitudes. The output of the analytical model is taken as the disturbances for the numerical method. In the numerical solutions TELEMAC-2D software system is used for both dispersive and nondispersive modeling. The results of the dispersive and nondispersive models are compared to each other. Both temporal and spatial differences in the amplitudes and wave shapes are examined. The obtained results demonstrate that there are no noticeable differences between the dispersion and non-dispersion solutions except some special cases and some special landslide velocities.     

Scenarios of local tsunamis in the China Seas by Boussinesq model

The Okinawa Trench in the East China Sea and the Manila Trench in the South China Sea are considered to be the regions with high risk of potential tsunamis induced by submarine earthquakes. Tsunami waves will impact the southeast coast of China if tsunamis occur in these areas. In this paper, the horizontal two-dimensional Boussinesq model is used to simulate tsunami generation, propagation, and runnp in a domain with complex geometrical boundaries. The temporary varying bottom boundary condition is adopted to describe the initial tsunami waves motivated by the submarine faults. The Indian Ocean tsunami is simulated by the numerical model as a validation case. The time series of water elevation and runup on the beach are compared with the measured data from field survey. The agreements indicate that the Boussinesq model can be used to simulate tsunamis and predict the waveform and runup. Then, the hypothetical tsunamis in the Okinawa Trench and the Manila Trench are simulated by the numerical model. The arrival time and maximum wave height near coastal cities are predicted by the model. It turns out that the leading depression N-wave occurs when the tsunami propagates in the continental shelf from the Okinawa Trench. The scenarios of the tsunami in the Manila Trench demonstrate significant effects on the coastal area around the South China Sea.     

一个覆盖太平洋区域的地震海啸波幅预报系统及检验

基于线性长波方程和缓变地形近岸波幅格林公式建立了覆盖整个太平洋区域的准实时地震海啸波幅预报系统。系统利用了GPU并行加速技术,可在90 s之内完成太平洋区域32 h的海啸传播计算和中国沿海城市岸段的波幅特征值预报。筛选了自2006年以来的9次发生在太平洋区域,矩震级（Mw）超过8.0且资料丰富的历史地震海啸事件,对预报系统进行了后报检验。结果表明,线性长波模型能够很好的模拟海啸在大洋中的传播过程;格林公式能够较为准确的估算缓变水深和开阔地形条件下的近岸海啸最大波幅,波幅预警准确率可达80%,基本满足海啸预警需求。以2011年日本Mw9.0地震海啸为例,评估了该系统对中国城市岸段的波幅预警能力,结论基本合理。需要注意的是,利用该系统计算对海啸源特别敏感的近场海啸波幅可能产生较大偏差。提出了若要进一步提高定量海啸波幅预警的准确率,可从以下两个方面加强研究和业务实践:一是采用多数据联合反演方法提升海啸源的精度;二是提高格林公式的适用性,或者构建高效的近岸精细化海啸数值预报系统。     

越洋海啸的数值模拟及其对我国的影响分析

简要介绍了地震海啸产生的物理机制、海啸波在大洋中的传播特性以及海啸所具有的超强破坏力可能引发的巨大灾害;概述了全球地震海啸发生的频率和太平洋区域历史海啸的时空分布;整理分析了我国沿海发生海啸的频次和空间分布。针对越洋海啸传播的特点,采用基于波浪追逐原理和自适应网格加密技术的海啸数值模型对1960智利海啸进行了数值模拟,将模拟的结果与历史记录进行了对比,验证了模型的可靠性。通过对数值模拟结果的分析,初步讨论了我国沿海地区越洋海啸的危险性,并定量阐述了越洋海啸对我国各海区的影响。     

The effects of variable speeds of a submarine block slide on near-field tsunami amplitudes

In this study, the motion of a submarine block slide, with variable velocities, and its effects on the near-field tsunami amplitudes are investigated. The numerical results show that the amplitudes generated by the slide are almost the same as those created by its average velocity when , where is average velocity of the slide and is the long period tsunami velocity in ocean of constant depth h. In contrast, the kinematic model of the slide must take into account time variations in the moving velocity, if , especially when .     

Deep water signature of a tsunami

The dynamics of tsunamis can be divided, for convenience, into three parts: tsunami generation, tsunami propagation, and the coastal problems. Out of these three, the problem of tsunami propagation is probably better understood than the other two. One of the main hindrances to the quantitative prediction of tsunami amplitudes at various coastal locations is a lack of detailed knowledge about the deep water signature of a tsunami. Here, the present understanding of this problem is discussed.     

Assessment of tsunami hazard for coastal areas of Shandong Province,China

Shandong province is located on the east coast of China and has a coastline of about 3100 km. There are only a few tsunami events recorded in the history of Shandong Province, but the tsunami hazard assessment is still necessary as the rapid economic development and increasing population of this area. The objective of this study was to evaluate the potential danger posed by tsunamis for Shandong Province. The numerical simulation method was adopted to assess the tsunami hazard for coastal areas of Shandong Province. The Cornell multi-grid coupled tsunami numerical model (COMCOT) was used and its efficacy was verified by comparison with three historical tsunami events. The simulated maximum tsunami wave height agreed well with the observational data. Based on previous studies and statistical analyses, multiple earthquake scenarios in eight seismic zones were designed, the magnitudes of which were set as the potential maximum values. Then, the tsunamis they induced were simulated using the COMCOT model to investigate their impact on the coastal areas of Shandong Province. The numerical results showed that the maximum tsunami wave height, which was caused by the earthquake scenario located in the sea area of the Mariana Islands, could reach up to 1.39 m off the eastern coast of Weihai city. The tsunamis from the seismic zones of the Bohai Sea, Okinawa Trough, and Manila Trench could also reach heights of >1 m in some areas, meaning that earthquakes in these zones should not be ignored. The inundation hazard was distributed primarily in some northern coastal areas near Yantai and southeastern coastal areas of Shandong Peninsula. When considering both the magnitude and arrival time of tsunamis, it is suggested that greater attention be paid to earthquakes that occur in the Bohai Sea. In conclusion, the tsunami hazard facing the coastal area of Shandong Province is not very serious; however, disasters could occur if such events coincided with spring tides or other extreme oceanic conditions. The results of this study will be useful for the design of coastal engineering projects and the establishment of a tsunami warning system for Shandong Province.     

海上丝绸之路海啸灾害危险分析

海上丝绸之路不仅是商业和贸易的通道, 也是东西方文化友谊的道路。2004年印度洋海啸对丝路沿线的多个沿海国家造成了重大破坏。因此需要对海啸发生规律和危害进行分析, 以确保海上丝绸之路上经济和文化交流的安全。为探索和识别海上丝绸之路上的海啸灾害, 本文给出了历史海啸事件的特征和规律。从震源震级、震源深度和水深等震源参数中发现了一些历史海啸数据背后的有用信息。本文还探讨了不同震级引起海啸的概率问题。分析结果表明：海上丝绸之路上的海啸主要发生在8个主要构造断层, 每个断层都有不同的海啸发生规律。在统计分析的基础上, 本文采用数值模型模拟了海上丝绸之路沿岸的潜在海啸,计算结果展示了海上丝绸之路沿岸的潜在海啸灾害程度。本文的研究成果有助于海啸灾害预警, 能够为保证海上丝绸之路贸易交流的安全提供科学参考。     

Numerical investigation of tsunami-like wave hydrodynamic characteristics and its comparison with solitary wave

Solitary waves have been commonly used as an initial condition in the experimental and numerical modelling of tsunamis for decades. However, the main component of a tsunami waves acts at completely different spatial and temporal scales than solitary waves. Thus, use of solitary waves as approximation of a tsunami wave may not yield realistic model results, especially in the coastal region where the shoaling effect restrains the development of the tsunami wave. Alternatively, N-shaped waves may be used to give a more realistic approximation of the tsunami wave profile. Based on the superposition of the sech²(*) waves, the observed tsunami wave profile could be approximated with the N-shaped wave method, and this paper presents numerical simulation results based on the tsunami-like wave generated based on the observed tsunami wave profile measured in the Tohoku tsunami. This tsunami-like wave was numerically generated with an internal wave source method based on the two-phase incompressible flow model with a Volume of Fluid (VOF) method to capture the free surface, and a finite volume scheme was used to solve all the governing equations. The model is first validated for the case of a solitary wave propagating within a straight channel, by comparing its analytical solutions to model results. Further, model comparisons between the solitary and tsunami-like wave are then made for (a) the simulation of wave run-up on shore and (b) wave transport over breakwater. Comparisons show that use of these largely different waveform shapes as inputs produces significant differences in overall wave evolution, hydrodynamic load characteristics as well as velocity and vortex fields. Further, it was found that the solitary wave uses underestimated the total energy and hence underestimated the run-up distance.     

2016年全球地震海啸监测预警与数值模拟研究

回顾了国家海洋环境预报中心(国家海洋局海啸预警中心)2016年全球地震海啸监测预警的总体状况, 并基于震源生成模型和海啸传播数值模型的计算结果详细介绍了几次主要海啸事件及其影响特性。2016年全年国家海洋环境预报中心总共对全球6.5级(中国近海5.5级)以上海底地震响应了45次,发布海啸信息81期, 没有发生对我国有明显影响的海啸。结合精细化的数值模拟结果和浮标监测数据,重点介绍了苏门达腊7.8级地震海啸、厄瓜多尔7.8级地震海啸、新西兰7.1级和7.8级地震海啸, 以及所罗门7.8级地震海啸的波动特征和传播规律, 模拟结果与实测海啸波符合较好。针对厄瓜多尔7.8级地震海啸事件, 本文比较分析了均匀断层模型和多源有限断层模型对模拟结果的影响; 针对新西兰7.1级地震海啸, 探讨了色散效应对海啸波在大水深、远距离传播过程的影响规律。     

Modeling the near-field effects of the worst-case tsunami in the Makran subduction zone

As a first step towards the development of inundation maps for the northwestern Indian Ocean, we simulated the near-field inundation of two large tsunami in the Makran subduction zone (MSZ). The tsunami scenarios were based on large historical earthquakes in the region. The first scenario included the rupture of about 500 km of the plate boundary in the eastern MSZ, featuring a moment magnitude of M_w 8.6. The second scenario involved the full rupture of the plate boundary resulting from a M_w 9 earthquake. For each scenario, the distribution of tsunami wave height along the coastlines of the region is presented. Also, detailed runup modeling was performed at four main coastal cities in the region for the second scenario. To investigate the possible effect of splay fault branching on tsunami wave height, a hypothetical splay fault was modeled which showed that it can locally increase the maximum wave height by a factor of 2. Our results showed that the two tsunami scenarios produce a runup height of 12-18 m and 24-30 m, respectively. For the second scenario, the modeled inundation distance was between 1 and 5 km.     

Managing tsunamis through early warning systems: A multidisciplinary approach

This study attempts to identify the key factors that will make a tsunami warning system most effective, to develop a framework in which results of natural science and engineering research can be effectively integrated into coastal natural hazard planning, and to develop a numerical example that illustrates how benefit-cost analysis may be used to assess early warning systems. Results of the study suggest that while the science of tsunami wave propagation and inundation is relatively advanced, our knowledge on the relationships between tsunami generation and undersea earthquakes, volcanic eruptions, and landslides remains poor, resulting in significant uncertainties in tsunami forecasting. Probabilities of damaging tsunamis for many coastal regions are still unknown, making tsunami risk assessment and management difficult. Thus it is essential to develop new techniques to identify paleo-tsunami events and to compile and develop size and frequency information on historical tsunamis for different locations. An effective tsunami early warning system must include not only the ocean technologies for accurately detecting an emerging tsunami, but also a civil communication system through which the population can be timely warned by the local government and other sources. Since minimizing the evacuation time is a key factor to make a warning system effective, adequate pre-event education and preparation of the population must be a critical component of the system. Results of a numerical example of the South Pacific region suggest that investments in a tsunami warning system in the region may lead to significant economic benefits.     

Numerical Simulation of Tsunamis on the Tamil Nadu Coast of India

The State of Tamil Nadu was the most affected region in India during the tsunami of December 26, 2004, in the Indian Ocean, in terms of loss of life and damage. Numerical simulation was made for three tsunamis, the December 26, 2004, event, the Sumatra tsunami of 1833, and a hypothetical tsunami originating in the Andaman-Nicobar region. Since inundation is not included in these simulations, the tsunami amplitudes were deduced at the 10m depth contour in the ocean, off several locations on the coast of Tamil Nadu. The computed amplitudes appear reasonable as compared to known tsunami amplitudes from past events.     

The Kuril Earthquakes and tsunamis of November 15, 2006, and January 13, 2007: Observations,analysis, and numerical modeling

Major earthquakes occurred in the region of the Central Kuril Islands on November 15, 2006 (M _w = 8.3) and January 13, 2007 (M _w = 8.1). These earthquakes generated strong tsunamis recorded throughout the entire Pacific Ocean. The first was the strongest trans-Pacific tsunami of the past 42 years (since the Alaska tsunami in 1964). The high probability of a strong earthquake (M _w ≥ 8.5) and associated destructive tsunami occurring in this region was predicted earlier. The most probable earthquake source region was investigated and possible scenarios for the tsunami generation were modeled. Investigations of the events that occurred on November 15, 2006, and January 13, 2007, enabled us to estimate the validity of the forecast and compare the parameters of the forecasted and observed earthquakes and tsunamis. In this paper, we discuss the concept of “seismic gaps,” which formed the basis for the forecast of these events, and put forward further assumptions about the expected seismic activity in the region. We investigate the efficiency of the tsunami warning services and estimate the statistical parameters for the observed tsunami waves that struck the Far Eastern coast of Russia and Northern Japan. The propagation and transformation of the 2006 and 2007 tsunamis are studied using numerical hydrodynamic modeling. The spatial characteristics of the two events are compared.     

The near-field tsunami amplitudes caused by submarine landslides and slumps spreading in two orthogonal directions

The aim of this study is to present the solutions for the near-field tsunami amplitudes caused by submarine landslumps and slides spreading in two orthogonal directions. A linearized shallow water wave theory is derived. The transform techniques (Fourier and Laplace transform) are used for the solution of Laplace equation. The results show that if the ratio of the velocties is v₁/v₂=0.1, the numerical results are almost the same as the values obtained for one dimensional movement of the slumps and slides. But, when the ratio of the velocties is v₁/v₂=1, obtained normalized peak amplitudes, η_max/ζ₀ are smaller than the numerical values for one dimensional solution. It is concluded that normalized peak amplitudes for the models are small because of the interaction of the velocities. Numerical examples are presented for various parameters.     

Numerical analysis of the propagation and amplification of tsunami waves on the northwest shelf of the Black Sea

We perform the numerical analysis of the process of propagation of long waves in the northwest part of the Black Sea and consider ten possible zones of the seismic generation of tsunamis. The numerical analysis is performed on a grid with steps of 500 m. It is shown that the location of the tsunami source significantly affects the distribution of the heights of waves along the coast. As a rule, the most intense waves are formed in the closest part of the coast. The earthquakes in the South-Coast seismic zone do not lead to the formation of tsunamis in the west part of the sea. Only strong earthquakes in the northwest part of the sea can be responsible for noticeable oscillations of the Black-Sea level. The period of tsunamis near Odessa is close to 1 h and depends on the magnitude of the earthquake. In the region of Sevastopol, this period is 2--3 times smaller. In the major part of the coastal points, the extreme elevations and lowerings of the sea level do not exceed (in modulus) the initial displacements of the sea surface at the source of tsunamis. An intensification of waves emitted from the zones of generation located in the deeper part of the investigated region was observed for some parts of the Romanian coast and the west coast of Crimea. As the magnitude of the earthquake increases, the intensification of waves near the coast becomes more pronounced.     

A Record of Palaeo-Tsunami in the Indian Ocean

The history of catastrophic events on the Indian coast helps us to understand the frequency and magnitude of the tsunamis that occurred in the Indian Ocean. These catastrophic events have changed the coastal landscape and have left significant records for further studies. These rare events have occurred in the Indian Ocean. There have been megatsunamigenic events in the past due to volcanic eruptions and earthquakes. Those events due to earthquakes have proved more catastrophic than the volcanic activities. There has been limited official records of the causality and magnitude of palaeo-tsunamigenic events. These have been studied using the various proxies. The rate of sedimentation is a proportional tool to study the magnitude of a tsunami and this has proved to be a successful tool along with foraminiferal assemblages. Causes for a tsunami to occur are by and large, the subduction zone earthquakes of the Indian plate has been the most common source for tsunami in the Indian Ocean. More often the Andaman and Nicobar and the Indonesian islands have been vulnerable to tsunami than the mainland of India and Sri Lanka.

In summary, in the last 200 years at least three basin-wide tsunamis have occurred, with several smaller tsunami affecting one or more coastlines in the region. The December 2004 M-9 tsunami seems to have been the largest and most destructive in the last two centuries, suggesting most tsunami are likely to be smaller but still allowing the possibility that even larger tsunami could be generated in propitious circumstances.     

Near-field tsunami amplification factors in the Kii Peninsula,Japan for Dense Oceanfloor Network for Earthquakes and Tsunamis (DONET)

We investigated the correlation between coastal and offshore tsunami heights by using data from the Dense Oceanfloor Network for Earthquakes and Tsunamis (DONET) observational array of ocean-bottom pressure gauges in the Nankai trough off the Kii Peninsula, Japan. For near-field earthquakes, hydrostatic pressure changes may not accurately indicate sea surface fluctuations, because ocean-bottom pressure gauges are simultaneously displaced by crustal deformation due to faulting. To avoid this problem, we focused on the average waveform of the absolute value of the hydrostatic pressure changes recorded at all the DONET stations during a tsunami. We conducted a Monte Carlo tsunami simulation that revealed a clear relationship between the average waveforms of DONET and tsunami heights at the coast. This result indicates the possibility of accurate real-time prediction of tsunamis by use of arrays of ocean-bottom pressure gauges.     

Tsunami Wave Interaction with Data Buoys

To plan for proper mitigation measures, one should have an advanced knowledge of the phenomenon of tsunami propagation from the deep ocean to coastal waters. There are a few methods to predict tsunamis in the ocean waters; one method is the effective use of data buoy measurements. Although data buoys have been used along the Indian waters there has been a tremendous growth in the number of buoy deployment recently. Under the National Data Buoy Programme (NDBP) of India, the 2.2 m diameter discus data buoys were deployed along the east and west coasts of India for measuring meteorological and ocean parameters. It would be advantageous if these buoys could be efficiently used to measure rare events such as tsunamis. Understanding the dynamic behavior of the buoy is of prime importance if a tsunami warning system is to be successful. This may be accomplished through experimental or numerical studies. A comprehensive experimental study has been conducted to understand the dynamic behavior of a wave rider buoy exposed to a variety of waves. It is common that tsunami waves are represented in terms of shallow water waves, namely solitary and cnoidal waves. Hence, in the present study, the discus type data buoy is scale modeled and tested under the action of solitary and cnoidal waves in the laboratory. The time histories of wave elevations, as well as heave and pitch motions of the buoy model, were analyzed through a spectral approach as well as through wavelet transformations. The wavelet approach gives more detailed insight into the spectral characteristics of the buoy motion in the time scale. The harmonic analyses were performed for the cnoidal wave elevations and subsequent motion characteristics that give an insight into the energy variations. The details of the model, instrumentation, testing conditions and the results are presented in this paper.     

Tsunami amplitudes from local earthquakes in the pacific northwest region of North America part 1: The outer coast

Abstract

Maximum tsunami amplitudes that will result from major earthquakes in the Pacific Northwest region of North America are considered. The modeled region encompasses the coastlines of British Columbia in Canada, and Washington and Oregon in the United States. Three separate models were developed for the outer coast and one model for the system consisting of the Strait of Georgia, Juan de Fuca Strait, and Puget Sound (GFP model) (Part 2). Three different source areas were considered for the outer coast models and the resulting tsunami was propagated to the entrance of Juan de Fuca Strait. Using the output from the other models, the GFP model was run. The results showed that large tsunami amplitudes can occur on the outer coast, whereas inside the GFP system, unless the earthquake occurs in the system itself, no major tsunami will result (Part 2).