Characteristics of the Oceanic Lithosphere and the Propagation of Pn and Sn Seismic Phases

太平洋海底地震仪记录的地震记录包含了有关地球构造板块结构和演化的重要信息。例如，当一个板块最初在洋中脊附近形成时，当板块冷却时，融冰的豆荚会被困在板块内。这些冰融物的组成与周围的物质不同，因此改变了地震波的传播方式。该项目计划检查部署在西太平洋的两个海底地震仪阵列记录的现有数据。新的观测和建模技术将用于寻找在构造板块形成期间放置的熔体荚。该项目的一个重要方面是调和岩石圈-软流圈边界的相互竞争的模型，即从坚硬的岩石圈板块到下面更柔软的岩石的过渡。某些类型的地震观测相当令人信服地表明，软流层相对于上覆板块（岩石圈）的机械强度较弱，但如果是这样的话，就很难解释记录到的地震波的存在。一个将被彻底探索的假设是，添加小尺度结构，如冻结的融冰袋，可以调和这两种观测结果。该项目支持培养一名博士后研究员和本科生。Pn波和Sn波——在岩石圈内传播的高频导波——为探测岩石圈的精细结构提供了为数不多的方法之一。在此项目期间，将对西太平洋海底地震仪（OBS）的两个阵列记录的Pn和Sn波进行详细分析。除了传统的尾波整体形状建模方法外，通过对详细波形的研究，可以更好地解析旧海洋岩石圈的整体速度结构、岩石圈内非均质性的幅度和尺度以及岩石圈的衰减结构。反过来，这些观测将增加我们对岩石圈形成过程的理解。该方法将结合详细的数据分析，使用新的分析技术，应用于比以往更高质量的Pn和Sn记录，并在三维非均质介质中对地震波的传播进行广泛的建模。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。

Earthquake recordings made by seismometers at the bottom of the Pacific Ocean contain important information about the structure and evolution of Earth's tectonic plates. When a plate initially forms near a mid-ocean ridge, for example, pods of melt can become trapped within the plate as it cools. These pockets of frozen melt have a different composition than the surrounding material and as such, alter how seismic waves propagate. This project plans to examine existing data recorded by two arrays of ocean-bottom seismometers deployed in the western Pacific. Novel observational and modeling techniques will be used to search for pods of melt emplaced during the formation of the tectonic plate. An important aspect of the project is to reconcile competing models of the lithosphere-asthenosphere boundary, that is, the transition from the rigid lithospheric plate to the more pliable rock below. Certain types of seismic observations suggest quite convincingly that the asthenosphere is mechanically weak relative to the overlying plate (lithosphere) but if this is the case, it is difficult to explain the existence of the seismic waves that are recorded. One hypothesis, which will be explored thoroughly, is that the addition of small-scale structures such as the frozen melt pockets can reconcile the two observations. The project supports the training of a postdoctoral investigator as well as undergraduate students.Pn and Sn waves - high frequency guided waves traveling within the lithosphere - provide one of the few ways that the fine-scale structure of the lithosphere can be probed. A detailed analysis of Pn and Sn waves recorded on two arrays of ocean-bottom seismometers (OBS) in the western Pacific will be carried out during this project. By examining the detailed waveforms in addition to the traditional approach of modeling the overall shape of the coda, it will be possible to resolve the overall velocity structure of old oceanic lithosphere better, the amplitude and scale of heterogeneities within the lithosphere, and the attenuation structure of the lithosphere. In turn, these observations will add to our understanding of the processes of lithospheric formation. The approach will be to combine detailed data analysis using new analytical techniques applied to more high quality Pn and Sn records than ever available before with extensive modeling of propagation of seismic waves in 3-D heterogeneous media.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.