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侧重于波在地球内部的传播速度，但地震能量的衰减速度也是人们最感兴趣的。地震衰减通过热激活过程进行，因此是地幔内温度变化的一个非常敏感的指标。因此，结合波速变化和衰减变化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。了解地震衰减的基础数据是地震波的振幅，但振幅受很多因素的影响，固有衰减甚至不是地震振幅的最大贡献者。因此，事实证明，很难获得地球内部地震衰减的可靠图像。我们使用基模面波的地震振幅(和相位)的超大数据集来解决这个问题。我们使用的方法并不是新的，它涉及到试图直接估计影响面波幅度的各种因素。这一建议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引起的幅度异常对地震波场的影响--地震波场是面波幅度异常的主要贡献者之一。由于相位和幅度效应通过物理频散效应交织在一起，我们的研究也将有助于更好地理解地震波的频散，从而更好地理解上地幔的弹性结构。我们的数据集足够大，足以研究各向异性对面波传播的影响--这本身就是一个重要的研究课题。这项研究侧重于提高我们对地震波传播的理解，重点是了解地震能量在地球上是如何衰减的。能够准确地模拟地震波在地球内和地球上的传播具有许多社会意义。我们给出三个例子。首先，存在地震危险性的问题，其中能够在大地震后准确地模拟地震幅度是至关重要的。其次，还有能够可靠地监测禁止核试验的问题。能够定位和估计任何类型的地震事件的大小对这一努力至关重要。最后，作为这项研究的一部分，我们还将完善数千次地震的震源模型。提高我们对震源的理解对社会具有明显的内在利益。

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.