南海潜在海啸传播过程的数值模拟:初始海啸衰减的影响  

Numerical modeling of potential tsunami propagation in the South China Sea:effects of initial tsunami attenuation

作　　者：杨少华[1,2,3] 石耀霖 YANG ShaoHua;SHI YaoLin(Key Laboratory of Continental Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China;Jiangsu Donghai Continental Deep Hole Crustal Activity National Observation and Research Station,Donghai Jiangsu 222300,China;Key Laboratory of Computational Geodynamics,College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国地质科学院地质研究所,自然资源部大陆动力学重点实验室,北京100037 [2]南方海洋科学与工程广东省实验室(广州),广州511458 [3]江苏东海大陆深孔地壳活动国家野外科学观测研究站,江苏东海222300 [4]中国科学院大学地球与行星科学学院,计算地球动力学重点实验室,北京100049

出　　处：《地球物理学报》2023年第9期3802-3815,共14页Chinese Journal of Geophysics

基　　金：中国地质调查局项目(DD20221630);南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项(GML2019ZD0201);国家自然科学基金项目(41830217);自然资源部深地动力学重点实验室自主(开放)研究课题(J1901-22)资助。

摘　　要：准确预估南海海啸风险是有效防灾减灾的前提.前人一般把弹性半无限空间背景下解算出来的海底位错直接等同于初始海啸分布,继而开展海啸传播过程研究.由于断层破裂并非瞬时完成,破裂过程会导致初始海啸波高小于海底位错量,即初始海啸衰减.本文基于高精度地形和高密度网格,求解非线性浅水方程,分别针对马尼拉断裂带的南段、中段和北段,构建南海海啸传播数值模型,试图定量考察初始海啸衰减作用对南海海啸的影响.模拟结果表明一定幅度的初始波高衰减将导致几乎相同幅度的海啸波高衰减,相应的偏差可以忽略.在保守的初始海啸衰减幅度(10%)下,模拟结果显示我国东南沿海、越南东部沿海和巴拉望岛为海啸危险区.另外,模型显示科里奥利力导致的波高变化幅度小于5 cm且其分布样式符合预期,这进一步佐证了数值模型的可靠性,也表明在实际南海海啸模拟中可以忽略科里奥利力进而提高计算效率.结合前人的沉积学认识和本文的数值模拟结果,本文认为南澳岛、西沙东岛和越南绥和周边曾同时遭受海啸侵袭,产生海啸的断裂带最有可能是马尼拉断裂带南段.后续有必要加强南澳岛、西沙东岛和越南东部的沉积学研究,识别更早的海啸事件,以期有力约束南海下次海啸事件的发生年份.Accurate assessments of tsunami risk are a prerequisite of effective disaster prevention and mitigation.Traditionally,seafloor dislocations calculated in the elastic semi-infinite space are given as initial tsunami distribution,and then tsunami propagation is studied numerically.Since the natural fault rupture is incompletely instantaneous,the initial tsunami heights will be less than seafloor dislocations,that is,initial tsunami attenuation(ITA).At present,the quantitative relationship between ITA and the relevant tsunami wave heights remains unclear.This quantitative relationship is investigated in this study through constructing a series of high-precision hydrodynamic numerical models:a case study of the South China Sea(SCS).Two significant controlling factors are involved in our numerical models:the magnitude of ITA,and the segmentation of the Manila fault zone(MFZ)which is assumed to lead the tsunami in the SCS.It is no surprise that ITA can reduce the tsunami height in the SCS in our models.Numerical results further reveal that the ratio of tsunami height reduction is directly proportional to the magnitudeof ITA with a negligible error(2.5%).That means if we know the magnitude of ITA,we will immediately obtain tsunami wave heights without performing numerical modeling.With a conservative initial tsunami attenuation(10%),the simulation results show that the southeast coast of China,the east coast of Vietnam and Palawan Island are tsunami hazard zones.In addition,the model shows that the magnitude of wave height due to Coriolis force is less than 5 cm and the distribution pattern is as expected,which further confirms the reliability of the numerical model and shows that the Coriolis force can be ignored in the actual South China Sea tsunami simulation to improve the computational efficiency.The combination of the previous sedimentary evidence and the current numerical experiment suggests that a 1000-year-ago damaging tsunami occurred in the SCS,most likely resulted from the southern segment of the MFZ,and was

关 键 词：海啸危险性 初始海啸衰减 数值模拟 科里奥利力 南海 

分 类 号：P313[天文地球—固体地球物理学] P738[天文地球—地球物理学]