Application of Uniform Slip Models to Tsunami Early Warning: A Case Study of 2021 Mw 8.2 Alaska Peninsula Earthquake
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摘要: 为了保证海啸预警的时效性，复杂的地震震源经常被简化为均匀滑移模型来预测海啸波. 虽然均匀滑移模型已经被广泛使用，但其在实际事件中预测海啸波的准确性并未得到全面的评估和认可.对2021年Mw 8.2 Alaska地震构建了有限断层模型(finite⁃fault model)和多种均匀滑移模型，并对海啸波的预测误差进行对比分析.有限断层模型显示，2021年Alaska地震的同震滑移分布在15~40 km的深度范围内，震源周围的最大滑移约为6 m. 另外，通过全局搜索得到的最优均匀滑移模型对海啸波的预测与有限断层模型非常接近，都与观测波形符合良好；两种位于gCMT中心、但采用不同标度关系(scalingrelation)的均匀滑移模型给出了几乎一致的远场波形.对此次地震海啸的研究结果表明，均匀滑移模型对海啸波的最佳预测能力与有限断层模型相当，根据gCMT中心和标度关系构造的均匀滑移模型对远场海啸预警比较可靠，且不同标度关系对远场波形预测无显著影响.
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关键词:
- 海啸预警 /
- 均匀滑移模型 /
- 海啸反演 /
- 2021年Alaska地震 /
- 天然地震
Abstract: To issue tsunami warnings in real⁃time, complex earthquake sources are usually simplified to uniform slip models for tsunami prediction. Althought this approach of simplification is widely used, its accuracy in predicting tsunami waves in actual events hasnot been fully evaluated and recognized. In this paper, a finite⁃fault model and various uniform slip models are constructed for the 2021 Mw 8.2 Alaska Peninsula earthquake, and their prediction errors for tsunami waves are compared. The finite⁃fault model inverted from tsunami datareveals that the coseismic slip of this event was distributed over a depth range of 15 to 40 km, and the ~6m maximum slip occurred near the hypocenter. Besides, the optimum uniform slip model obtained from global search provides very similar tsunami predictions to those given by the finite⁃fault model, both of which agree well with the observations. Two uniform slip models located at the gCMT centroid but using different scaling relations yield almost the same far⁃field waveforms.Results of this study show that the optimum predicting ability of uniform slip modelis almost equivalent to that of the finite⁃fault model. The uniform slip models based on gCMT centroids and scaling relations are relatively reliable for far⁃field tsunami warning, and difference in scaling relations may not significantly impact the far⁃field predictions.-
Key words:
- tsunami warning /
- uniform slip model /
- tsunami inversion /
- 2021 Alaska Peninsula earthquake /
- earthquake
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图 1 Alaska⁃Aleutian俯冲带周边大洋水深以及2021年Alaska地震的源区几何位置
a. 震中周围水深及海啸观测分布，DART浮标和潮位站分别由品红色三角形和白色倒三角标出；b. 假定源区和子断层划分，白色小方块代表子断层，4个角上的子断层序号用黑色数字标出，红色和蓝色五角星分别为USGS震中和gCMT中心；c. 地形和板间界面沿垂直于走向的直线A⁃B的截面，灰色和绿色曲线分别为Slab2.0模型和有限断层模型的深度剖面，灰色沙滩球为1976—2021年源区内逆冲地震gCMT中心的垂直投影
Fig. 1. Bathymetry around the Alaska⁃Aleutian subduction zone and the source geometry of 2021 Mw 8.2 earthquake
图 2 2021年Alaska地震的4种滑移模型
a. 海啸数据反演得到的有限断层模型；b. 全局搜索得到的最优均匀滑移模型；c. 基于gCMT中心和标度关系An2018的均匀滑移模型；d. 基于gCMT中心和标度关系Blaser2010的均匀滑移模型
Fig. 2. Four slip models for 2021 Mw 8.2 Alaska Peninsula earthquake
图 3 有限断层模型和最优均匀滑移模型预测的海啸波与观测波形的对比
Fig. 3. Comparison of tsunami waveforms between observations and those predicted bythe finite⁃fault model and the optimum uniform slip model
图 4 有限断层模型和最优均匀滑移模型预测的海啸首波振幅、到时和观测数据的对比
Fig. 4. Comparison of first tsunami wave amplitude and arrival time between observations and those predicted by the finite⁃fault model and the optimum uniform slip model
图 5 基于gCMT中心和两种标度关系的均匀滑移模型造成的初始水面变形
Fig. 5. Initial sea surface displacement caused by uniform slip models based on the gCMT centroid and two scaling relations
图 6 基于gCMT中心和两种标度关系的均匀滑移模型预测的海啸波与观测波形的对比
Fig. 6. Comparison of tsunami waveforms between observations and those predicted by uniform slip models based on the gCMT centroid and two scaling relations
图 7 基于gCMT中心和两种标度关系的均匀滑移模型预测的首波振幅、到时和观测数据的对比
Fig. 7. Comparison of first tsunami wave amplitude and arrival time between observations and those predicted by uniform slip models based on the gCMT centroid and two scaling relations
表 1 4种滑移模型对海啸波振幅和到时的预测误差
Table 1. Prediction errorsof four slip models for tsunami amplitude and arrival time
有限断层模型 最优均匀滑移模型 位于gCMT中心(An 2018) 位于gCMT中心(Blaser 2010) 振幅误差(cm, 相对误差) 0.83(17.8%) -0.3(-6.4%) 1.5(31.6%) 0.5(10.5%) 到时误差(min, 相对误差) -4.4(-6.2%) -1.1(-1.6%) 3.5(5.0%) 2.0(2.9%) 
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