Investigating the Lithosphere-Asthenosphere System by Integrating New Constraints on Seismic Attenuation with Existing Geophysical Observations

地震波通过真正的弹性材料传播，原则上会永远传播下去。在地球中，各种机制使地震能量从波中“泄漏”出来，使得它不能用于进一步传播;最终导致能量的耗散。这就是所谓的地震衰减。虽然地震衰减发生在几秒钟内，但控制这一现象的一些机制对板块在数百万年时间尺度上对构造应力的反应方式产生了深远的影响。出于这个原因，了解地震衰减的强弱可以帮助解决以下问题：断裂（伸展事件在板块上留下的疤痕）如何影响板块的强度？而且，是什么控制了山脉和地震发生在远离板块边界的位置？此外，地幔岩石中少量熔体的影响可能会或可能不会显著影响衰减，这取决于熔体在岩石基质中的分布。因此，了解可能含有熔体的地区的衰减可以帮助我们了解熔体在上地幔中的位置和方式。地震衰减在野外和实验室中都相对难以研究，因此对衰减结构的限制比深层地下的其他属性（主要是地震传播速度）要少得多。该项目将采用最近开发的一种强有力的方法，对地球镜倡议产生的高质量地震数据集进行大陆下面衰减结构的成像。选择了几个焦点站点，这些站点已被FlexArray地震部署覆盖，并且代表了本项目旨在调查的特征的主要示例。此外，将生成的新结果与其他地球物理信息相结合，将为项目提出的问题提供比单独使用任何一种技术更有力的答案。衰减测量结果将与以前对地震速度和电导率（如果可用）的限制相结合，使用由EarthScope资助的另一个项目开发的软件工具进行联合分析，以辨别观察到的异常是否可以通过温度升高，少量熔体的存在，含水量增加等因素得到最好的解释。最后，作为该项目一部分开发的数据分析软件将得到加强，建立直观的用户界面和独立的软件包，供科学界使用。促进这些工具的传播和使用将降低进行此类测量和进行此类研究的障碍。这项工作的广泛影响是多方面的。作为本提案的一部分，用于处理衰减的MATLAB代码将向社区公开发布。通过将代码与直观的GUI配对，新进入该领域的科学家将能够更容易地测量电磁体波的衰减。该提案将资助一名博士后研究员和一名西班牙裔早期职业PI。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Seismic waves propagating though a truly elastic material would, in principle, keep on propagating forever. In the Earth, various mechanisms make the seismic energy "leak" out of the waves, such that it is not available for further propagation; leading eventually to the dissipation of the energy. This is what is known as seismic attenuation. Although seismic attenuation occurs in a matter of seconds, some of the same mechanisms that control this phenomenon have profound effects on the way the plates respond to tectonic stresses over millions-of-years timescales. For this reason, understanding where seismic attenuation is strong and weak can help address questions such as: How do failed rifts (scars left on the plates by episodes of extension) affect the strength of the plates? And, what controls the location of mountain ranges and earthquakes that occur away from the plate boundaries? Additionally, the effect of small amounts of melt in mantle rocks may or may not significantly affect attenuation depending on how that melt is distributed within the rock matrix. Therefore, understanding attenuation in what are likely melt-bearing regions can help us understand where and how melt is retained in the upper mantle.Seismic attenuation is relatively difficult to study both in the field and in the lab, and thus constraints on attenuation structure are much scarcer than those available for other properties of the deep subsurface, primarily seismic propagation velocity. This project will apply a recently developed robust methodology for imaging the attenuation structure beneath the continents to the high-quality seismic data sets that have resulted from the EarthScope initiative. Several focus sites were selected that have been covered by FlexArray seismic deployments and that represent prime examples of the features that this project is aiming to investigate. Furthermore, combining the new results that will be generated with other geophysical information will provide stronger answers to the questions the project poses than would have been possible with any one technique alone. The attenuation measurements will be combined with previous constraints on seismic velocity and conductivity (where available) jointly analyzed using software tools developed by another EarthScope-funded project to discern whether the observed anomalies are best explained by factors such as enhanced temperature, presence of small amounts of melt, enhanced water content, or others. Finally, the data analysis software developed as part of this project will be enhanced by building intuitive user interfaces and self-contained software packages that will be made available to the scientific community. Facilitating the dissemination and use of these tools will lower the barriers to making this kind of measurement and doing this kind of research. Broader Impacts of the work are many. The MATLAB code used to process attenuation as part of this proposal will be publicly released to the community. By pairing the code with an intuitive GUI, scientists new to the field will more easily be able to measure the attenuation of teleseismic body waves. This proposal will fund one postdoctoral researcher and a Hispanic early career PI.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.