海啸波对近岸岛礁影响的数值模拟研究

Numerical study of tsunami impact on coastal reef

基于Okada有限断层模型和非线性浅水波方程,结合高精度嵌套网格建立了越洋(中国近海)-局部-近岸岛礁的海啸生成与传播的数值模型。以三亚凤凰岛为例,首先针对2011日本地震海啸,模拟分析了海啸波沿中国沿海大陆架的传播特征及对凤凰岛的影响规律。在取得验证结果的基础上,进一步讨论了中国近海的马尼拉海沟和琉球海沟的潜在海啸源,以及环太平洋的21个潜在特大越洋海啸对凤凰岛的影响特征。依据海啸波在抵达凤凰岛的波浪特征,结合傅里叶频谱分析方法,探索了近岸岛礁对海啸波的放大效应。结果表明,中国近海一般震级的海啸和特大越洋海啸对凤凰岛存在一定影响,最大波幅接近1m,传播时间从3h到27h不等。受三亚东南半岛的影响,琉球海沟激发的海啸和越洋海啸在凤凰岛的放大效应相对于马尼拉海沟较小,其频率集中在0.8×10-4~2×10-4 Hz。马尼拉海沟产生的海啸波在凤凰岛产生了较为显著的放大效应,对于凤凰岛是值得关注的高风险海啸源。

In this study, tsunami generation and propagation model involved trans-Pacific （China＇s offshore） -local- coastal reef has been established, based on Okada model, nonlinear shallow water equations, and coupled grid with high resolution. The Phoenix Island in Sanya City is selected as research subject. Firstly, the simulation of 2011 Japan Tohoku tsunami has been carried out, and the characteristics of tsunami propagation along the continental shelf of Chinese coasts and the impacts on Phoenix Island are presented, combined with real-time measurements. The impacts of tsunami source along Manila Trench, Ryukyu Trench, and 21 extreme sources around Pacific on Phoenix Island are discussed. According to characteristics of tsunami wave near the Phoenix Island, the amplifica- tion effect of tsunami wave near coastal reef is discussed based on Fouriers analysis. It turns out that relatively moderate tsunami near Chinese coasts and extreme trans-Pacific tsunami will have some impacts on Phoenix Island, which may induce tsunami of maximum amplitude reached 1 m. The travel time ranges from 3 h to 27 h. Due to the impact of southeast peninsula Sanya, tsunami from Ryukyu Trench and trans-Pacific tsunami will generate less amplification effect than Manila Trench due to wave diffraction, whose frequency are in the range of 0.8 ×10^-4-2×10^-4 Hz. The tsunami from Manila Trench may produce obvious amplification effect, and require more attention.