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

将地震衰减新约束与现有地球物理观测相结合研究岩石圈-软流圈系统

• 批准号: 1827277
• 负责人: Maximiliano Bezada
• 金额: $ 25万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-01 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1827277&HistoricalAwards=false
• 关键词: Investigating; Lithosphere; Asthenosphere; System; Integrating

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.

在真正的弹性材料中传播的地震波，原则上会一直传播下去。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。尽管地震衰减发生在几秒钟内，但控制这一现象的一些相同的机制对板块对数百万年时间尺度上的构造应力的反应方式产生了深远的影响。出于这个原因，了解地震衰减在哪里强和弱可以帮助解决这样的问题：失败的裂缝(伸展事件在板块上留下的伤疤)如何影响板块的强度？那么，是什么控制了远离板块边界的山脉和地震的位置呢？此外，地幔岩石中少量熔体的影响可能会也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，了解可能含有熔体的区域中的衰减可以帮助我们了解熔体在哪里以及如何被保存在上地幔中。地震衰减在野外和实验室中都相对较难研究，因此对衰减结构的约束比对深部地下其他特性的约束要少得多，主要是地震传播速度。该项目将把最近开发的一种强有力的方法用于成像大陆以下的衰减结构，并将地球范围倡议产生的高质量地震数据集应用于此。选择了几个已被FlexArray地震部署覆盖的焦点地点，这些地点代表了本项目旨在调查的特征的主要例子。此外，与单独使用任何一种技术相比，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更有力的答案。衰减测量将与以前对地震速度和传导性(如果有)的约束结合在一起，使用另一个由EarthScope资助的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最好地由温度升高、少量熔体的存在、水分含量增加等因素解释。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向科学界提供的自成一体的软件包而得到加强。促进这些工具的传播和使用将降低进行这种测量和研究的门槛。这项工作的更广泛影响是多方面的。作为这项提案的一部分，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图形用户界面配对，新进入该领域的科学家将更容易测量远程地震体波的衰减。这项提议将资助一名博士后研究员和一名西班牙裔早期职业PI。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Dynamic Upwelling Beneath the Salton Trough Imaged With Teleseismic Attenuation Tomography

• DOI: 10.1029/2020jb020347
• 发表时间: 2020-06
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: J. Byrnes;M. Bezada

Thin lithosphere beneath the central Appalachian Mountains: Constraints from seismic attenuation beneath the MAGIC array

• DOI: 10.1016/j.epsl.2019.04.045
• 发表时间: 2019-08
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: J. Byrnes;M. Bezada;M. Long;M. Benoit

Evidence for Stress Localization Caused by Lithospheric Heterogeneity From Seismic Attenuation

• DOI: 10.1029/2021gc009987
• 发表时间: 2021-06
• 期刊: Geochemistry
• 影响因子: 3.7
• 作者: Zhao Zhu;M. Bezada;J. Byrnes;H. Ford

On the robustness of attenuation measurements on teleseismic P waves: insights from micro-array analysis of the 2017 North Korean nuclear test

• DOI: 10.1093/gji/ggz169
• 发表时间: 2019-04
• 期刊: Geophysical Journal International
• 影响因子: 2.8
• 作者: M. Bezada;J. Byrnes;Z. Eilon