港湾中海啸流的模拟及其时空演变特征对输入条件不确定性的响应分析

摘要

The tsunami wave characteristics have been widely used as crucial parameters to characterize potential destruction.The characterization has better adaptability especially for the disaster caused by the near-field extreme tsunami events.However,analyzing the losses caused by the historical tsunami events,we can conclude that the strong current induced by tsunamis is the main cause of damage in the coastal zone and harbors.The rapid water level change caused by continental shelf and harbors oscillations may lead to strong current.It may be a threat tomaritime facilities.Effective response and reduced tsunami current hazards will be a new challenge for tsunami warning services and maritime emergency management.It was particularly urgent to develop numerical forecasting methods and tsunami warning guidance products for tsunami vortex flows in bays and harbors.It's very meaningful for us to comprehensively understand and assess the characteristics of tsunami disasters in harbors.Due to limitation of field observation and lack of knowledge on the generation of tsunami vortex flows,the most of research on tsunami mainly focus on the characteristics of tsunami waves and tsunami-induced flooding.There is few research on the tsunami-induced currents,which may result in incomplete understanding of tsunami disaster in harbors and bays.Three high resolution tsunami numerical models were established for harbors which located in Hawaiian Islands based on nonlinear shallow water equation model (MOST).The horizontal resolution are all up to 10 meter.Far-field tsunami wave and current characteristics from Tohoku-oki earthquake are analyzed relied on finite-fault rupture model.The simulated results show that the tsunami characteristics in all the three harbors and their adjacent areas are in good agreement with the measured results.The refinement tsunami models are credible.This paper also highlight that tsunamis damage is not exclusively caused by surges that result in coastal inundation.There may be small amplitude accompanied by strong currents.We present the results of numerical investigation that how scenario-maximum amplitudes and tsunami-induced currents vary due to the different input conditions.The following conclusions were drawn from the above studies.First,the spatial distribution characteristics of tsunami surge and currents in harbors are distinctly different,which is related to tsunami standing wave behaviors.Second,tsunami current has much greater spatial sensitivity relative to spatial variability of wave amplitude,and it is strong around the harbor entrance.The spatiotemporal evolution of tsunami currents has a stronger response to the uncertainties of input conditions than tsunami wave amplitude.The accurate simulation for tsunami-induced current is more challenging.Third,the influence on the accuracy of tsunami current simulation caused by the input uncertainties were responsibility for the error of tsunami risk assessment.So reasonable input conditions are critical to accurate tsunami flows estimating.Finally,the results of this paper can help us to comprehensively understand the characteristics of coastal tsunami disaster from surge and tsunami currents.They were very helpful for improving tsunami warning technology.So as to provide more scientific decision support products for disaster emergency management in future.%一直以来,海啸波特征作为表征海啸潜在破坏性的参数指标得到了广泛应用,特别是针对近场极端海啸事件造成的灾害来说,这种表征具有较好的适用性.然而总结分析历史海啸事件造成的损失发现:在远场近岸及港湾系统中,海啸诱导的强流却是造成损失的主要原因.陆架或港湾振荡导致海啸波幅快速升降诱发强流,可能促使港工设施受到威胁及损害,进而对海啸预警服务及海事应急管理提出了新的挑战.因此,全面理解与评估海啸在港湾中诱发的灾害特征,探索港湾中海啸流的数值模拟方法,发展针对港湾尺度的海啸预警服务指导产品尤为迫切.受限于海啸流验证数据的缺乏及准确模拟海啸流技术方法的诸多不确定性,大部分海啸数值模拟研究工作主要是针对水位特征的研究及验证,可能导致对港湾中海啸灾害危险性认识的曲解与低估.本研究基于非线性浅水方程,针对夏威夷群岛三个典型港湾建立了精细化海啸数值模型(空间分辨率达到10 m),并联合有限断层破裂模型计算分析了日本东北地震海啸在三个港湾及其邻近区域的海啸特征,波、流计算结果与实测结果吻合较好,精细化的海啸港湾模型模拟结果可信.模拟发现港湾中较小的波幅,同样可以产生强流.综合分析日本东北地震海啸波、流特征对输入条件不确定性的响应结果发现:港湾中海啸波-流能量的空间分布特征差异较大,这与港湾系统中海啸波的驻波特性相关;相比海啸波幅空间特征,海啸流特征具有更强的空间敏感性;海啸流时空分布特征对输入条件的不确定性响应比海啸波幅对这些不确定性的响应更强,海啸流的模拟与预报更有挑战性;不确定性对海啸流计算精度的影响会进一步传导放大港湾海啸流危险性的评估及对港工设施产生的应力作用的误差,合理的输入条件对海啸流的精确模拟至关重要.最后,希望通过本文的研究可以从海啸波-流特征角度更加全面认识近岸海啸灾害特征,拓展海啸预警服务的广度与深度,从而为灾害应急管理部门提供更加科学合理的辅助决策产品.