Wave attenuation mechanism of cross-plates applied in landslide-induced tsunami in river course

Since the impounding of the Three Gorges Reservoir, the channel of the Yangtze River has become a busy watercourse and the probability of landslide-induced tsunamis has increased. In the case of landslide-induced tsunamis in the Three Gorges Reservoir, even after shipping closures in advance,there are still facilities and objects in urgent need of protection within the risk zone of the watercourse,such as wharfs, marine fueling stations, berthed ships.The emergency protection against and decay of landslide-induced tsunamis in inland watercourses is a new challenge. In this study, 37 sets of wave decay experiments were conducted with the hydromechanics numerical method. The wave decay efficiencies of common simple structures including submerged horizontal plate, horizontal plate on the water surface,inclined thin plate and cross-plates in coastal areas were compared and analyzed. Cross-plates structure showed better wave decay capacity than other simple plates. The wave decay performance of cross-plates was related to five modes of energy dissipation and transformation, namely run-up/run-down, overtopping,reflecting, return flow and disturbed wave orbital path. The type of wave had little relation with the decay performance of cross-plates, but a strong correlation with cross-plates structure, especially the height of the vertical emerged plate. The best decay performance was observed when the ratio of wave amplitude to emerged vertical plate height was between 1 and 1.5, which can reduce up to about 80%of the incoming wave amplitude. Finally, the emergency way of cross-plates applied to the decay of landslide-induced tsunami in river course is discussed.This study provides a conceptual reference for related studies to practice the attenuation of landslide-induced tsunami in reservoirs.

Simulation on 2D underwater landslide-induced tsunamis

The Green-Naghdi （GN） theory is used here to simulate two-dimensional （2D） underwater landslide-induce tsunamis. Finite difference method is used to solve the GN equations. GN theory has different levels. There are GN-1, GN-2, .--, GN-K theory in GN theory. When K goes up, the GN equations will be more complicated, and the results will be more accurate. For the case simulated here, results of GN-5 theory are better than results of GN-3 theory. GN-7 results are almost the same as GN-5 results. That means GN-5 results are the converged results from GN theory. GN-5 results agree well with other＇s experimental results.

A TPDP-MPM-based approach to understanding the evolution mechanism of landslide-induced disaster chain

With complex topographic and hydrological characteristics,the landslide-induced surge disaster chain readily develops in mountainous and gorge areas,posing a huge challenge for infrastructure construction.This landslide-induced surge disaster chain involves a complex fluid-solid coupling between the landslide mass and a water body and exhibits complex energy conversion and dissipation characteristics,which is challenging to deal with using traditional finite element analysis.In this study,the energy evolution characteristics in the whole process of the disaster chain were first investigated,and the momentum-conservation equations for different stages were established.Then,the two-phase doublepoint material point method(TPDP-MPM)was used to model the landslide-induced surge disaster chain,and an experiment involving block-induced surge was modeled and simulated to validate this method.Finally,three generalized models were established for the landslide-induced surge process in a U-shaped valley,including subaerial,partly submerged,and submarine scenarios.The interaction mechanism between the landslide mass and the water body in the disaster chain was revealed by defining the system energy conversion ratio and the mechanism of evolution of the disaster chain from the perspective of energy.The results help further evaluate the secondary disasters,given the submerged position of the landslide mass.

Rigid block characteristics on subaerial landslide-tsunamis using a 3D coupled Eulerian-Lagrangian model

To quantitatively reveal how rock blocks falling into water affect the impulse waves,the influence of a rigid block on induced first wave and second wave is systematically investigated.The block characteristics include the initial velocity,density,volume,and incident angle,and the investigated wave behavior characteristics include the maximum kinetic energy of the water,the transformation ratio of the kinetic energy from the block to the waves,the duration of the waves,the maximum movement speed,and the maximum height and width of the waves.The coupled Eulerian-Lagrangian method(CEL)is introduced to establish the numerical models of the fluid-solid coupling,and a laboratory test of a rigid wedge sliding into water demonstrates that it can reasonably describe the dynamic behavior of a landslide-induced wave.A typical process of a block entering water and its energy variation are described and analyzed in detail.Further,the relationship between each characteristic parameter of the block and the waves is quantitatively investigated and fitted.The simulation results show that energy exchange between the block and the water is very rapid after the block collides with the water.The maximum kinetic energy,maximum velocity,duration,and side dimension of the waves mainly increase non-linearly with the above characteristic parameters of the block.The transformation ratio of the kinetic energy from the block to the water,the first wave,and the second wave are usually below 60%,45%,and 30%,respectively.The velocity of the block first decreases and then maintains a constant speed after entering the water.The displacement of the block increases linearly with the initial velocity and density of the block and exponentially increases with the block volume at different times.With the increase in the incident angle of the block,the kinetic energy and scale of the second wave increase correspondingly.

Experimental study on the mitigation effect of mangroves during tsunami wave propagation

Mangroves are crucial for protecting coastal areas against extreme disasters such as tsunamis and storm surges.An experimental study was conducted to determine how mangroves can mitigate the tsunami wave propagation.The test was performed in a flume, where mangrove models were installed on a slope, and dam-burst waves were used to simulate tsunami waves. To study how mangrove forests reduce the impact of tsunamis, this paper measured the heights of the incoming waves under different initial conditions(tsunami wave intensity and initial water depth) and plant factors(arrangement and distribution density) and described the reduction process. The results show that, after passing through the mangrove, the tsunami bore height will decrease within a certain range as the initial water depth increases. However, there is no correlation between the increase of inundation level and the drop of water level. The bore height attenuation is more significant at higher density of mangroves,but after tsunami passing through the mangroves, the relative bore height will decrease. When the distribution density of mangroves is constant, the wave attenuation at different locations(before, on and after the slope)shows different relationships with the initial water depth and wave height for different models. The transmission coefficient(K_(i)) shows a parabolic correlation with its density. The proportion of the energy loss caused by the mangrove resistance to the total energy(E_(b)) is defined as C_(m2). The variation trend of C_(m2) corresponds to the tsunami wave energy attenuation rate(C_(a)) and K_(i).

Tsunami Hazard Assessment on Qatar Coastline from Makran Earthquakes Considering Tidal Effect and Coastal Landslides Scenarios

To assist the analysis of tsunami hazards for Qatar coastal areas were using numerical model. By Tsunamis waves created from submarine earthquakes of magnitude of (Mw) 8.6 and 9.0 in Richard scale along the Makran Subduction Zone (MSZ) as well as coastal landslides with soil volume of 1.25 to 2.0 km3 along Iranian coast inside the Arabian Gulf is considered. TUNAMI-N2KISR model (Al-Salem) was applied in this study to predict the tsunami propagation and magnitude of Tsunami induced wave heights. The model adopts to solve shallow water equations describing nonlinear long-wave theory. The model also incorporate tidal effect inside the Arabian Gulf as a tsunami travel time from Makran Subduction to Qatar coastline takes more than 9 hours with the tidal range of about 1.6 m during Spring Tide event. For coastal landslides, tsunami generation was simulated using a two-layer numerical model, developed by solving nonlinear long-wave equations. Two-layer model was used to determine initial wave deformation generated by a landslide case. Then TUNAMI-N2KISR was use to simulate tsunami wave propagation. Tsunami waves from landslide scenario arrived after 2.5 - 3 hr with maximum tsunami amplitudes along coasts of Ras laffan-Qatar were 0.8 to 1.0 m. Incorporation of ocean tide is found to impose some small effect on tsunami amplitude at Qatar coastline and nearby areas for the Mw 9.0 earthquake due to small tidal range in this area. In addition, it is found that the tsunami arrival time has become shorter.

Radio Direction Finding Method to Mitigate Tsunami Risk in Sierra Leone

In this study,the Radio Direction Finding method is proposed for the detection of electromagnetic signals,in the VLF band,to try to anticipate the occurrence of potentially destructive geophysical events.The experimentation concerns the interception of electromagnetic anomalies in Sierra Leone,in the five-day time window,associated with seismic events that could potentially generate tsunamis.The area of investigation is Sierra Leone,whose coastline is subjected to tidal wave hazards triggered by earthquakes generated in the Mid-Atlantic Ridge.Although Sierra Leone is not affected by recurrent earthquakes,there is nevertheless a low probability,estimated at 2 percent,of the occurrence of destructive earthquakes in the next 50 years.Also in estimates,the risk of rogue and potentially damaging waves is estimated to strike the Sierra Leone coast at least once in the next 10 years.The Radio Direction Finding experiment carried out continuously 24/7,has shown a close relationship between increased radio-anomalies,in the frequencies of 6,000 Hz,a time window between electromagnetic anomaly detection and the imminence of an earthquake,and higher frequency times for the risk of earthquake occurrence in the Mid-Atlantic Ridge.

震源运动学破裂过程对马尼拉俯冲带潜在海啸的影响研究

提高对马尼拉俯冲带海啸生成机制的认识对研究我国东南沿海地区海洋防灾减灾具有重要意义。目前,大型俯冲带震源破裂的运动过程对海啸生成的影响逐渐受到关注,但震源运动学破裂过程对马尼拉俯冲带潜在海啸的影响尚未明确。基于马尼拉俯冲带的典型破裂模型,对不同破裂速度和方向设定的海啸情景开展数值模拟,评估分析破裂速度和方向对海啸波传播特征的影响。结果表明:破裂方向相同时,破裂速度越慢,海啸波到时越晚,峰值波高越小;破裂速度相同时,与不考虑破裂运动过程的模拟结果相比,破裂前方的场点峰值波高更大,距离初始破裂位置更近的场点到时越早;不同设定情境下,沿海场点的海啸波到时最大相差10 min左右,峰值波高最大值约为最小值的1.5倍。

海啸作用下滨水挡土墙抗震滑动稳定性上限分析

针对沿海地区滨水挡土墙在海啸和地震联合作用下易发生被动破坏的问题,结合极限分析上限法和拟静力法确定地震荷载,研究了海啸作用下滨水挡土墙的抗震滑动稳定性。通过建立墙体滑动与破坏区土楔体整体滑动的墙-土系统及速度容许场,推导出水平地震加速度系数(kh)的表达式。分析了海啸、海平面与地下水高度及墙-地和墙-土摩擦角对地震屈服加速度系数的影响。结果表明,控制地下水位在适当高度并增大墙-土摩擦角可以有效提高滨水挡土墙的抗震滑动稳定性。与经典极限平衡理论相比,该方法考虑了土体的塑性流动及挡土墙的位移模式,且无需计算地震被动土压力的值。

卷积神经网络方法在岛礁类海啸波水动力特性演变的应用

海啸是严重的海洋灾害,准确的海啸预测对于海洋工程和人民生命财产安全具有重要意义。本文以一维卷积神经网络(1-dimensional convolutional neural network,CONV1D)为基础,构建岛礁地形的类海啸波水动力特性演变模型。通过输入类海啸波波高时程曲线的观测值,得到岛礁指定地点的水位淹没时程曲线,实现时间序列到时间序列的预测,进行海洋灾害的实时预报,提前布置防御措施以达到减小损失的目的。结果显示,预测一组样本所需时间少于一秒,相对于传统的地震海啸预警系统,深度学习方法所需计算资源较少,计算速度更快。对类海啸波到达时间预测的平均相对误差为0.71%,最大水位高度预测的平均相对误差为6.99%, CONV1D得到的岛礁地形类海啸波水动力特性与数值结果吻合较好。

耦合震级、震源深度和滑动角不确定性效应的地震海啸危险性估计

选取中国东南沿海地区6个近岸场点,以马尼拉海沟俯冲带和琉球海沟俯冲带作为潜在地震海啸源区,采用广义极值地震活动性模型和广义帕累托地震活动性模型分析震级不确定性特征,通过统计震源深度的优势分布和拟合滑动角分布函数,耦合震级、震源深度和滑动角不确定性效应,得到两个俯冲带对6个场点未来30 a、50 a、100 a海啸波高超过0.4 m的地震海啸危险性估计结果。结果表明:百年内舟山近海和宁德近海特定场点遭受地震海啸袭击风险较低,随着时间的推移,从位于厦门近海至香港近海、海口近海和高雄近海的特定场点,地震海啸危险性递增。

河北省海啸灾害风险评估和区划研究

基于康奈尔多电网耦合海啸模型(COMCOT)数值模式建立研究区海啸数值模型,利用模型对6个地震海啸源情景场进行模拟计算,通过对各海啸源下数值模拟结果的综合分析,确定研究区海啸灾害危险性分布;根据土地利用类型数据资料确定研究区承灾体脆弱性分布;通过危险性、脆弱性评估成果,综合确定研究区海啸灾害风险性评估和区划成果。结果表明:河北省遭受海啸灾害风险最高等级为Ⅱ级,主要分布在唐山市和秦皇岛市沿海区域;沧州市沿海区域海啸灾害风险等级较小,为Ⅲ级和Ⅳ级。

Modeling the dynamic process of tsunami earthquake by liquid-solid coupling model

Tsunami induced by earthquake is an interaction problem between liquid and solid.Shallow-water wave equation is often used to modeling the tsunami,and the boundary or initial condition of the problem is determined by the displacement or velocity field from the earthquake under sea floor,usually no interaction between them is consid-ered in pure liquid model.In this study,the potential flow theory and the finite element method with the interaction between liquid and solid are employed to model the dynamic processes of the earthquake and tsunami.For model-ing the earthquake,firstly the initial stress field to generate the earthquake is set up,and then the occurrence of the earthquake is simulated by suddenly reducing the elastic material parameters inside the earthquake fault.It is dif-ferent from seismic dislocation theory in which the relative slip on the fault is specified in advance.The modeling results reveal that P,SP and the surface wave can be found at the sea surface besides the tsunami wave.The surface wave arrives at the distance of 600 km from the epicenter earlier than the tsunami 48 minutes,and its maximum amplitude is 0.55 m,which is 2 times as large as that of the sea floor.Tsunami warning information can be taken from the surface wave on the sea surface,which is much earlier than that obtained from the seismograph stations on land.The tsunami speed on the open sea with 3 km depth is 175.8 m/s,which is a little greater than that pre-dicted by long wave theory,(gh)1/2=171.5 m,and its wavelength and amplitude in average are 32 km and 2 m,respectively.After the tsunami propagates to the continental shelf,its speed and wavelength is reduced,but its amplitude become greater,especially,it can elevate up to 10 m and run 55 m forward in vertical and horizontal directions at sea shore,respectively.The maximum vertical accelerations at the epicenter on the sea surface and on the earthquake fault are 5.9 m/s2 and 16.5 m/s2,respectively,the later is 2.8 times the former,and therefore,sea water is a good shock absorber.The acceleration at the sea shore is about 1/10 as large as at the epicenter.The maximum vertical velocity at the epicenter is 1.4 times that on the fault.The maximum vertical displacement at the fault is less than that at the epicenter.The difference between them is the amplitude of the tsunami at the epicenter.The time of the maximum displacement to occur on the fault is not at the beginning of the fault slipping but retards 23 s.

海底火山喷发大气冲击波激发的轴对称海啸波数值模型

海底火山喷发引发海啸具有多源激发机制,包括水下爆炸、边坡失稳、火山口坍塌、碎屑流、地震以及大气扰动.为了深入认识轴对称移动气压扰动激发海啸的机理,探究气压扰动参数对水波形态的影响规律,本文在柱面孤立波Boussinesq模型的基础上,考虑水面移动气压扰动作用,建立了由火山喷发激发的轴对称移动气压场所驱动的海啸波数值模型.利用不同地形上柱面波的传播算例验证了本模型的精确性与稳定性.数值模拟了2022年汤加火山喷发大气扰动激发海啸事件,并与太平洋DART浮标实测数据比较,较好地复演了大气扰动驱动海啸波的远场传播过程,并讨论了波动在深水区的色散行为.研究了轴对称气压扰动的径向移速、强度及尺度对波动演化特征的影响,结果显示:气压移速与浅水波速的相对大小显著影响波形,当二者接近时将激发Proudman共振.在共振条件下,波幅与径向传播距离呈近似线性增长关系,波幅放大因子随气压尺度增大而减小.在远离共振条件时,气压强度和尺度对波幅放大因子的影响相对较小,受波能流守恒约束柱面自由波幅则沿程衰减,受迫波幅值近似按气压衰减规律变化.

马尼拉俯冲带地震海啸对华南沿海的概率性灾害影响

马尼拉俯冲带地震作为高风险海啸源对华南沿海地区构成严重威胁,开展概率性海啸灾害评估有助于全面了解马尼拉俯冲带地震海啸能量的时空分布规律并指导南海海岸工程的设计及建设。本文针对马尼拉俯冲带五项不确定性参数的概率分布展开研究,应用逻辑树法设计地震海啸样本集,使用非静压海啸数值模型对所有样本情景进行传播模拟,最后通过概率计算得到南海海域的海啸最大波幅超越概率曲线,并绘制了100年和500年回归周期下南海概率性海啸最大波幅的空间分布图。研究发现,100年一遇的海啸对中国大陆南部沿海影响较低,潜在海啸的最大波幅最高可达0.7 m,危险等级不超过Ⅱ级;500年一遇的海啸可能会对我国南部沿岸城市(如汕头、汕尾、香港地区和澳门地区等)造成最大波幅为2.5 m左右的Ⅲ级海啸威胁,中沙群岛和西沙群岛沿岸可能出现最大波幅为3.1 m的海啸活动,东沙群岛受到最大波幅有可能超过4.0 m的海啸威胁,这些地区海啸危险等级均高达Ⅳ级。

Maximum initial primary wave model for low-Froude-number reservoir landslides based on wave theory

The impulse waves induced by large-reservoir landslides can be characterized by a low Froude number.However,systematic research on predictive models specifically targeting the initial primary wave is lacking.Taking the Shuipingzi 1#landslide that occurred in the Baihetan Reservoir area of the Jinsha River in China as an engineering example,this study established a large-scale physical model(with dimensions of 30 m×29 m×3.5 m at a scale of 1:150)and conducted scaled experiments on 3D landslide-induced impulse waves.During the process in which a sliding mass displaced and compressed a body of water to generate waves,the maximum initial wave amplitude was found to be positively correlated with the sliding velocity and the volume of the landslide.With the increase in the water depth,the wave amplitude initially increased and then decreased.The duration of pressure exertion by the sliding mass at its maximum velocity directly correlated with an elevated wave amplitude.Based on the theories of low-amplitude waves and energy conservation,while considering the energy conversion efficiency,a predictive model for the initial wave amplitude was derived.This model could fit and validate the functions of wavelength and wave velocity.The accuracy of the initial wave amplitude was verified using physical experiment data,with a prediction accuracy for the maximum initial wave amplitude reaching 90%.The conversion efficiency(η)directly determined the accuracy of the estimation formula.Under clear conditions for landslide-induced impulse wave generation,estimating the value ofηthrough analogy cases was feasible.This study has derived the landslide-induced impulse waves amplitude prediction formula from the standpoints of wave theory and energy conservation,with greater consideration given to the intrinsic characteristics in the formation process of landslide-induced impulse waves,thereby enhancing the applicability and extensibility of the formula.This can facilitate the development of empirical estimation methods for landslide-induced impulse waves toward universality.

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.

Trapping Mechanism of Submerged Ridge on Trans-oceanic Tsunami Propagation

Based on the linear shallow water equations,an analytic solution of trapped waves over a symmetric parabolicprofile submerged ridge is derived.The trapped waves act as propagating waves along the ridge and as standing waves across the ridge.The amplitude gets the maximum at the ridge top and decays gradually towards both sides.The decaying rate gets more gently with higher modes.Besides,an explicit first-order approximate dispersion relation is derived to simplify transcendental functions in the exact solution,which is useful to describe trapped waves over shallowly submerged ridges in reality.Furthermore,the trapping mechanism of the submerged ridge waveguides on the trans-oceanic tsunami propagation can be explained by the ray theory.A critical incident angle exists as a criterion to determine whether the wave is trapped.Besides,a trapped parameter γ is proposed to estimate the ratio of the energy trapped by the oceanic ridge if a tsunami is generated at its top.

The September 16, 2015 Mw 8.3 Illapel, Chile Earthquake： characteristics of tsunami wave from near-field to far-field

On September 16, 2015, an earthquake with magnitude ofMw 8.3 occurred 46 km offshore from Illapel, Chile, generating a 4.4-m local tsunami measured at Coquimbo. In this study, the characteristics of tsunami are presented by a combination of analysis of observations and numerical simulation based on sources of USGS and NOAA. The records of 16 DART buoys in deep water, ten tidal gauges along coasts of near-field, and ten coastal gauges in the far-field are studied by applying Fourier analyses. The numerical simulation based on nonlinear shallow water equations and nested grids is carried out to provide overall tsunami propagation scenarios, and the results match well with the observations in deep water and but not well in coasts closed to the epicenter. Due to the short distance to the epicenter and the shelf resonance of southern Peru and Chile, the maximum amplitude ranged from 0.1 m to 2 m, except for Coquimbo. In deep water, the maximum amplitude of buoys decayed from 9.8 cm to 0.8 cm, suggesting a centimeter-scale Pacific-wide tsunami, while the governing period was 13-17 min and 32 min. Whereas in the far-field coastal region, the tsunami wave amplified to be around 0.2 m to 0.8 m, mostly as a result of run-up effect and resonance from coast reflection. Although the tsunami was relatively moderate in deep water, it still produced non-negligible tsunami hazards in local region and the coasts of farfield.

Evolvement of tsunami waves on the continental shelves with gentle slope in the China Seas

Potential tsunami generated in the Okinawa Trench or the Manila Trench may attack the southeast coast of China. The continental shelves with extremely gentle slope in the China Seas affect the evolvement of tsunami waves. In this paper, we carry out the simulation of tsunami propagation based on the fully nonlinear and highly dispersive Boussinesq model, which could describe the nonlinearity and dispersion of water waves quite well. So the undulation characters could be well presented. In terms of the real topographies of the East China Sea and the South China Sea, we take some typical profiles to simulate the hypothetical tsunamis generated in the Okinawa Trench and the Manila Trench. Different waveforms in the near shore regions are obtained. The N-shape tsunami waves will evolve into long wave trains, undular bores or solitons near the coastal area. The numerical results of the near shore waveform provide essential conditions for the further studies of tsunami runup and inundation.