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

地震波通过真正有弹性的材料传播，原则上会永远传播下去。在地球上，各种机制使地震能量从波中“泄漏”出来，使其无法进一步传播；最终导致能量耗散。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相同机制对板块在数百万年的时间尺度上对构造应力的反应方式有着深远的影响。因此，了解地震衰减的强弱可以帮助解决以下问题：失效裂缝（板块伸展留下的疤痕）如何影响板块的强度？还有，是什么控制着远离板块边界的山脉和地震的位置？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方式。因此，了解可能存在熔体的区域的衰减可以帮助我们了解熔体在哪里以及如何保留在上地幔中。地震衰减无论是在野外还是在实验室研究都相对困难，因此对衰减结构的限制远远少于对深层地下其他性质（主要是地震传播速度）的限制。该项目将采用最近开发的一种强大的方法，对由EarthScope计划产生的高质量地震数据集进行大陆下衰减结构成像。FlexArray地震部署已经覆盖了几个重点站点，这些站点代表了该项目旨在研究的主要特征。此外，将产生的新结果与其他地球物理信息相结合，将为该项目提出的问题提供比单独使用任何一种技术可能提供的更有力的答案。衰减测量结果将与之前对地震速度和电导率的限制（如有）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，以确定观测到的异常是否可以用温度升高、存在少量熔体、含水量增加或其他因素来最好地解释。最后，作为该项目的一部分开发的数据分析软件将通过建立直观的用户界面和将提供给科学界的独立软件包而得到加强。促进这些工具的传播和使用将降低进行这类测量和进行这类研究的障碍。这项工作的更广泛影响是多方面的。作为该提案的一部分，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，该领域的新科学家将更容易测量远震体波的衰减。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。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.