Ray Tracing for Dispersive Tsunamis and Source Amplitude Estimation Based on Green’s Law: Application to the 2015 Volcanic Tsunami Earthquake Near Torishima, South of Japan
Ray Tracing for Dispersive Tsunamis and Source Amplitude Estimation Based on Green’s Law: Application to the 2015 Volcanic Tsunami Earthquake Near Torishima, South of Japan
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DOI：
10.1007/s00024-017-1746-0
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发表时间：
2018-04
影响因子：
2
通讯作者：
Osamu Sandanbata;S. Watada;K. Satake;Y. Fukao;H. Sugioka;A. Ito;H. Shiobara
中科院分区：
文献类型：
--
作者：
Osamu Sandanbata;S. Watada;K. Satake;Y. Fukao;H. Sugioka;A. Ito;H. Shiobara
广泛用于地震波的射线追踪法也被用于海啸，以检查传播过程中的测深效果，但仅限于线性浅水波。绿色的法律，这是基于能量通量守恒，已被用来估计海啸振幅的射线路径。在这项研究中，我们首先提出了一个新的射线追踪方法扩展到分散海啸。通过使用迭代算法来映射不同频率下的二维海啸速度场，可以追踪每个频率下的射线路径。然后，我们表明，绿色的法律是有效的，只有在源区域和绿色的法律扩展是必要的源振幅估计。作为一个应用示例，我们分析了2015年日本鸟岛附近的海底火山史密斯火山发生的地震所产生的海啸波。射线追踪结果表明，射线路径非常依赖于它的频率，特别是在深海。我们的频率依赖的射线追踪的有效性得到证实的到达角和旅行时间与观察到的海啸波形在海底压力计阵列的比较。根据绿色定律，根据阵列海啸数据估计，震源处的海啸振幅几乎是震源外海啸振幅的两倍或更多。
Ray tracing, which has been widely used for seismic waves, was also applied to tsunamis to examine the bathymetry effects during propagation, but it was limited to linear shallow-water waves. Green’s law, which is based on the conservation of energy flux, has been used to estimate tsunami amplitude on ray paths. In this study, we first propose a new ray tracing method extended to dispersive tsunamis. By using an iterative algorithm to map two-dimensional tsunami velocity fields at different frequencies, ray paths at each frequency can be traced. We then show that Green’s law is valid only outside the source region and that extension of Green’s law is needed for source amplitude estimation. As an application example, we analyzed tsunami waves generated by an earthquake that occurred at a submarine volcano, Smith Caldera, near Torishima, Japan, in 2015. The ray-tracing results reveal that the ray paths are very dependent on its frequency, particularly at deep oceans. The validity of our frequency-dependent ray tracing is confirmed by the comparison of arrival angles and travel times with those of observed tsunami waveforms at an array of ocean bottom pressure gauges. The tsunami amplitude at the source is nearly twice or more of that just outside the source estimated from the array tsunami data by Green’s law.