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

太平洋底部地震仪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，当板块最初在大洋中脊附近形成时，当板块冷却时，融化的豆荚可能会被困在板块内。这些冰冻融化带与周围物质的成分不同，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。将使用新的观测和模拟技术来寻找在构造板块形成期间侵位的熔体豆荚。该项目的一个重要方面是协调岩石圈-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)是机械上弱的，但如果是这样的话，很难解释所记录的地震波的存在。一种将被彻底探索的假说是，小尺度结构的加入，如冻结的熔融口袋，可以与两种观察结果相一致。该项目支持对博士后研究人员和本科生的培训。Pn和Sn波--在岩石圈内传播的高频导波--提供了少数几种可以探测岩石圈精细结构的方法之一。在本项目期间，将对西太平洋两个海底地震仪记录的Pn波和Sn波进行详细分析。除了传统的模拟尾波整体形状的方法外，通过研究详细的波形，将有可能更好地解析旧大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，这些观察将增加我们对岩石圈形成过程的理解。该方法将使用新的分析技术进行详细的数据分析，应用于比以往任何时候都更高质量的PN和SN记录，并对三维非均匀介质中的地震波传播进行广泛的建模。该奖项反映了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。

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.