Combined analysis of surface wave phase and amplitude data using finite frequency kernals: Towards a detailed mode of attenuation in the upper mantle

对地球三维结构的研究通常集中在地球内波的传播速度上，但地震能量衰减的速率也是基本的兴趣。地震衰减通过热激活过程起作用，因此是地幔内温度变化的一个非常敏感的指标。因此，将波速变化与衰减变化相结合，为了解地球内部地震异常的物理原因提供了一个强大的工具。了解地震波衰减的基本数据是地震波的振幅，但振幅受许多因素的影响，固有衰减甚至不是地震振幅的最大贡献者。因此，事实证明很难得到地球内部地震衰减的可靠图像。我们使用非常大的数据集的地震振幅（和相位）的基模面波来解决这个问题。我们使用的方法并不新鲜，并试图直接估计影响表面波振幅的各种因素。该提案的新特点是使用更可靠的理论基础来评估聚焦和散焦效应对地震波场造成的振幅异常的影响-这是造成表面波振幅异常的主要因素之一。由于相位和振幅效应通过物理色散效应交织在一起，我们的研究也将提供更好的理解地震波的色散，从而上地幔的弹性结构。我们的数据集足够大，也可以解决各向异性对面波传播的影响-本身就是一个重要的研究课题。这项研究的重点是提高我们对地震波传播的理解，重点是了解地震能量如何在地球中衰减。能够准确地模拟地震波在地球内部和地球上的传播具有许多社会意义。我们举三个例子。首先，存在地震危险的问题，其中能够在大地震后准确地模拟地震振幅是至关重要的。第二，存在着能够可靠地监测核禁试的问题。能够定位和估计任何类型的地震事件的大小对这一奋进至关重要。最后，作为这项研究的一部分，我们还将改进数千次地震的震源模型。提高我们对地震源的认识显然对社会有着内在的利益。

Studies of the 3D structure of the Earth usually focus on the speed of wave propagation within the Earth, but the rate at which seismic energy is attenuated is also of fundamental interest. Seismic attenuation operates through thermally activated processes and is therefore a very sensitive indicator of temperature variations within the mantle. Thus, combining wave speed variations with attenuation variations gives a powerful tool for learning about the physical cause of seismic anomalies within the Earth. The fundamental datum for learning about seismic attenuation is the amplitude of seismic waves, but amplitudes are affected by so many things, and intrinsic attenuation is not even the strongest contributor to seismic amplitudes. Consequently, it has proven difficult to get a reliable picture of seismic attenuation within the Earth. We use extremely large datasets of the seismic amplitudes (and phase) of fundamental mode surface waves to address this problem. The approach we use is not new and involves trying to directly estimate the various factors affecting surface wave amplitudes. The new feature of this proposal is to use a more robust theoretical basis for assessing the effects of amplitude anomalies caused by focusing and defocusing effects on the seismic wavefield -- one of the main contributors to surface wave amplitude anomalies. Since phase and amplitude effects are intertwined through the effects of physical dispersion, our research will also provide improved understanding of the dispersion of seismic waves and consequently of the elastic structure of the upper mantle. Our datasets are sufficiently large to also address the effects of anisotropy on surface wave propagation -- in itself an important topic of investigation.This research focuses on improving our understanding of seismic wave propagation with an emphasis on understanding how seismic energy is attenuated in the Earth. Being able to accurately model the propagation of seismic waves in and on the Earth has many societal implications. We give three examples. Firstly, there is the issue of seismic hazard where being able to accurately model seismic amplitudes after a large earthquake is crucial. Secondly, there is the issue of being able to monitor a nuclear test ban reliably. Being able to locate and estimate the size of seismic events of any kind is critical to this endeavor. Finally, as part of this research, we will also be refining models of the seismic sources of many thousands of earthquakes. Improving our understanding of seismic sources is of obvious intrinsic interest to society.