Modal scattering: A key to understanding oceanic T‐waves
Modal scattering: A key to understanding oceanic T‐waves
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模态散射：理解海洋 T 波的关键
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
Darin J. Soukup
中科院分区：
文献类型：
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作者：
Minkyu Park;R. Odom;Darin J. Soukup
近五十年来，海洋 T 波的激发机制一直是一个谜，倾斜海底的折射和海底散射是最常被提及的两种机制。通过将震源场表示为简正模态和，可以看出这两种机制是非常密切相关的。严格的模态正交性禁止横向均匀半无限半空间或径向对称球体中存在 T 波，因为能量无法在均匀介质中从一种模式转移到另一种模式。确定性非平面测深、随机边界粗糙度、上地壳异质性或这些的组合提供了打破严格正交性的物理机制。我们表明，来自震中区域粗糙海底的模态散射将能量从直接激发的海洋地壳/水柱模式转换为由海洋 T 波组成的传播声模式。海底地震断层方向似乎也反映在 T 波激励中。
The excitation mechanism of oceanic T‐waves has been a puzzle for almost fifty years, with refraction from a sloping seafloor and seafloor scattering as two of the most commonly invoked mechanisms. By representing the earthquake source field as a normal mode sum, it can be seen that both mechanisms are very closely related. Strict modal orthogonality prohibits the existence of T‐waves in a laterally homogeneous semi‐infinite half‐space or radially symmetric sphere, as energy cannot be transferred from one mode to another in an homogeneous medium. Deterministic non‐planar bathymetry, random boundary roughness, upper crustal heterogeneity, or a combination of these provides a physical mechanism to break the strict orthogonality. We show that modal scattering from the rough seabottom in the epicentral region converts energy from the directly excited ocean crustal/water column modes to the propagating acoustic modes comprising the oceanic T‐wave. Submarine earthquake fault orientation also appears to be reflected in the T‐wave excitation.