Comparison of methods for coupled earthquake and tsunami modelling
Comparison of methods for coupled earthquake and tsunami modelling
复制标题
地震海啸耦合模拟方法比较
DOI：
10.1093/gji/ggad053
复制
发表时间：
2023
影响因子：
2.8
通讯作者：
Saito, Tatsuhiko
中科院分区：
文献类型：
--
作者：
Abrahams, Lauren S.;Krenz, Lukas;Dunham, Eric M.;Gabriel, Alice-Agnes;Saito, Tatsuhiko
近海地震引起的海啸是一个具有科学意义和实际意义的问题，需要为数据解释和危害评估建立数值模型。大多数数值模型使用两步方法，在单独的地震和海啸模型之间进行单向耦合，基于可能限制所得解的适用性和准确性的近似值。特别是，标准方法只关注海啸波的模拟，而忽略了在震源区域叠加在海啸波上的较大振幅的海洋声波和地震波。在本研究中，我们比较了四种地震海啸模拟方法。我们确定了无量纲参数来定量地近似地震海啸震源区域的主要波浪模式，强调方法假设如何影响结果，并讨论哪些方法适合各种应用，例如震源区域海上仪器数据的解释。大多数方法将提供地震波场或至少静态弹性位移的三维固体地球模型与二维深度平均浅水海啸模型相结合。假设海洋不可压缩，海啸传播在地震持续时间内可以忽略不计，则采用瞬时震源法，将静态地震海底隆起与海啸初始海面高度等同起来。对于持续时间较长的地震，采用时变震源法是合适的，该方法使用时变地震海底速度作为海啸物质平衡中的强迫项。这两种方法都不能捕捉到海洋声波或地震波，因此需要更先进的方法来捕捉整个波场。Saitoet al.采用叠加法求解三维弹性和声学方程，模拟无重力可压缩海洋的地震波场和响应。然后，在一个单独的海啸模拟中，使用零重力解的海面高度变化作为强迫项，通常使用浅水解算器运行。地震和海啸解的叠加提供了完整波场的近似值。这个方法在算法上是一个两步法。完整的波场是用全耦合方法捕获的，该方法利用固体地球和可压缩海洋的重力耦合模型。这种完全耦合的方法最近被纳入了3d开源代码SeisSol，可以同时解决地震破裂、地震波和海洋反应（包括重力）问题。我们表明，叠加方法出现作为一个近似的完全耦合的方法受制于往往是合理的假设。在此基础上，利用完全耦合方法研究了源谱和海洋深度对海洋瑞利波表达的影响。了解每种方法的有效范围及其计算费用，有助于选择准确评估地震和海啸危害的建模方法，并解释海上仪器的数据。
Tsunami generation by offshore earthquakes is a problem of scientific interest and practical relevance, and one that requires numerical modelling for data interpretation and hazard assessment. Most numerical models utilize two-step methods with one-way coupling between separate earthquake and tsunami models, based on approximations that might limit the applicability and accuracy of the resulting solution. In particular, standard methods focus exclusively on tsunami wave modelling, neglecting larger amplitude ocean acoustic and seismic waves that are superimposed on tsunami waves in the source region. In this study, we compare four earthquake-tsunami modelling methods. We identify dimensionless parameters to quantitatively approximate dominant wave modes in the earthquake-tsunami source region, highlighting how the method assumptions affect the results and discuss which methods are appropriate for various applications such as interpretation of data from offshore instruments in the source region. Most methods couple a 3-D solid earth model, which provides the seismic wavefield or at least the static elastic displacements, with a 2-D depth-averaged shallow water tsunami model. Assuming the ocean is incompressible and tsunami propagation is negligible over the earthquake duration leads to the instantaneous source method, which equates the static earthquake seafloor uplift with the initial tsunami sea surface height. For longer duration earthquakes, it is appropriate to follow the time-dependent source method, which uses time-dependent earthquake seafloor velocity as a forcing term in the tsunami mass balance. Neither method captures ocean acoustic or seismic waves, motivating more advanced methods that capture the full wavefield. The superposition method of Saitoet al. solves the 3-D elastic and acoustic equations to model the seismic wavefield and response of a compressible ocean without gravity. Then, changes in sea surface height from the zero-gravity solution are used as a forcing term in a separate tsunami simulation, typically run with a shallow water solver. A superposition of the earthquake and tsunami solutions provides an approximation to the complete wavefield. This method is algorithmically a two-step method. The complete wavefield is captured in the fully coupled method, which utilizes a coupled solid Earth and compressible ocean model with gravity. The fully coupled method, recently incorporated into the 3-D open-source code SeisSol, simultaneously solves earthquake rupture, seismic waves and ocean response (including gravity). We show that the superposition method emerges as an approximation to the fully coupled method subject to often well-justified assumptions. Furthermore, using the fully coupled method, we examine how the source spectrum and ocean depth influence the expression of oceanic Rayleigh waves. Understanding the range of validity of each method, as well as its computational expense, facilitates the selection of modelling methods for the accurate assessment of earthquake and tsunami hazards and the interpretation of data from offshore instruments.