The effect of sedimentary basins on surface waves that pass through them
The effect of sedimentary basins on surface waves that pass through them
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DOI：
10.1093/gji/ggx313
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发表时间：
2017-10
影响因子：
2.8
通讯作者：
Lili Feng;M. Ritzwoller
中科院分区：
文献类型：
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作者：
Lili Feng;M. Ritzwoller
摘要
穿过沉积盆地传播的面波会经历弹性波场的复杂变化，包括多次散射、放大、次生波前的形成以及随后的波前修复。除非准确考虑这些效应，否则它们可能会对震源特性的估计、地球非弹性结构的推断以及用于灾害评估的地面运动预测产生系统性偏差。大多数关于盆地对面波影响的研究都集中在盆地内部的波。相比之下，本文的目的是研究沉积盆地下游的波场效应，特别强调大陆盆地和传播路径、弹性结构非均质性以及10秒周期的瑞利波。基于通过一个最新的东亚三维地壳和上地幔模型进行的波场模拟，我们证明了中国东部沉积盆地下游存在显著的瑞利波放大现象，以至于在模拟波场上进行的面波震级（Ms）测量相差超过一个震级单位。我们表明，盆地引起的面波放大主要是由弹性聚焦导致的，并且通过一个适当定义的相速度图进行二维薄膜波模拟可以重现三维盆地模型产生的放大效应。二维和三维模拟中弹性聚焦的主要特征包括：（1）盆地内部波前的延迟；（2）波传播方向的偏转；（3）在盆地正下游形成一条由两个低振幅区包围的高振幅条带；（4）次生波前的形成。我们通过几个例子说明盆地的大小和几何形状如何影响聚焦。最后，通过比较弹性聚焦和非弹性衰减的影响，我们认为，除了在盆地边缘附近或对于具有极端纵横比的盆地外，大陆上的沉积盆地预计通过弹性聚焦对面波振幅的影响比通过非弹性衰减更为强烈。
S U M M A R Y Surface waves propagating through sedimentary basins undergo elastic wavefield complications that include multiple scattering, amplification, the formation of secondary wave fronts and subsequent wave front healing. Unless these effects are accounted for accurately, they may introduce systematic bias to estimates of source characteristics, the inference of the anelastic structure of the Earth, and ground motion predictions for hazard assessment. Most studies of the effects of basins on surface waves have centred on waves inside the basins. In contrast, the purpose of this paper is to investigate wavefield effects downstream from sedimentary basins, with particular emphasis on continental basins and propagation paths, elastic structural heterogeneity and Rayleigh waves at 10 s period. Based on wavefield simulations through a recent 3-D crustal and upper-mantle model of East Asia, we demonstrate significant Rayleigh wave amplification downstream from sedimentary basins in eastern China such that Ms measurements made on the simulated wavefield vary by more than a magnitude unit. We show that surface wave amplification caused by basins results predominantly from elastic focusing and that amplification effects produced through 3-D basin models are reproduced using 2-D membrane wave simulations through an appropriately defined phase velocity map. The principal characteristics of elastic focusing in both 2-D and 3-D simulations include (1) retardation of the wave front inside the basins; (2) deflection of the wave propagation direction; (3) formation of a high-amplitude lineation directly downstream from the basin bracketed by two low-amplitude zones and (4) formation of a secondary wave front. We illustrate with several examples how the size and geometry of the basin affects focusing. Finally, by comparing the impact of elastic focusing with anelastic attenuation, we argue that on-continent sedimentary basins are expected to affect surface wave amplitudes more strongly through elastic focusing than through the anelastic attenuation except near the edge of the basin or for basins with extreme aspect ratios.