Through the Ocean to the Mantle: Seismic Study of the Pacific Mantle with Long-Lived Autonomous Floating Seismic Sensors

地震仪记录地震产生的地震波。地震波速度的变化是由地球的温度和成分变化引起的。这些波速的变化是用来了解地球结构和演化的主要观测，从地幔对流的规模和热量从地核转移到地表的方式，到地球深部和地表过程（如构造板块运动和地壳变形）之间的相互作用。然而，记录地震波的地震仪的地理数据覆盖范围并不均匀，这仍然是地震研究的基本限制因素。由于地球表面的三分之二被海洋覆盖，很难在海洋中部署地震仪，这些地区的仪器覆盖率很低。因此，地球的所有三维模型都在很少或无法获得信息的区域用空白点标记。一个自主机器人地震传感器已经研制成功，并部署在法属波利尼西亚附近的太平洋上。该项目将分析来自这批移动的传感器的数据，以便对地球地幔中的小规模结构进行成像，并更好地了解地球的热历史。在本项目期间，将开发一个智能手机应用程序，用于K-12外联项目。该项目支持对学生进行海洋地质学和地球物理学、地幔层析成像、软件设计、教育和外联、统计和应用数学方面的培训，由于缺乏海洋地震数据，全球地震层析成像波速模型在中深地幔的分辨率仍然有限，妨碍了对地球未知内部进行更详细的勘探和解释性了解。部署和回收海底设备在技术上具有挑战性，而且成本高昂。低成本，自由浮动，自主水听器阵列提高了P波层析成像的分辨率。在一个国际财团的帮助下，在法属波利尼西亚部署了彩车，以记录今后五年抵达的海啸。在该项目的第一个两年阶段，将对近实时恢复的数据进行收集、质量控制、存档、记录和公开传播。将根据一维速度参考模型分析初至走时异常，着眼于创建适合区域层析反演的精选高质量数据集。海洋台阵走时异常的地震学分析将与根据附近陆地台站收集的记录构造的地幔过渡区接收函数所获得的新结果进行比较。与全球网络中的少数台站相比，该阵列的孔径有了很大的改进，因此，两条研究路线的结果将代表对地幔了解的具体改进。地幔层析成像受到数据可用性的限制;南半球的采样最差，那里是许多地幔柱的所在地，这些地幔柱驱动着冷却地球深部的热机。热点与深部地幔结构的联系仍然不确定。在这个项目中分析的新数据将被用来构建并最终回答关于现今地幔动力学和地球热演化的主要问题。这个奖项反映了NSF的法定使命，并被认为是值得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的支持。

Seismometers record seismic waves generated by earthquakes. Changes in seismic wave speeds are caused by variations in the temperature and composition of Earth. These changes in wave speeds are the primary observation used to understand the structure and evolution of Earth, from the scale of mantle convection and the way heat is transferred from the core to the surface to the interaction between deep Earth and surface processes such as tectonic plate motion and crustal deformation. Geographical data coverage by seismometers that record the seismic waves is not uniform, however, and this remains the fundamental limiting factor in seismic studies. Because two thirds of Earth's surface is covered by oceans, and it is difficult to deploy seismometers in the oceans, instrument coverage in these areas is sparse. Thus, all three-dimensional models of Earth are marked by blank spots in areas where little or no information can be obtained. An autonomous robotic earthquake sensor has been developed and deployed in the Pacific Ocean near French Polynesia. This project will analyze the data from this fleet of mobile sensors to image small-scale structures in Earth's mantle and provide a better understanding of the thermal history of Earth. An Adopt-a-Float smartphone app will be developed during this project and used in K-12 outreach projects. The project supports the training of students in marine geology and geophysics and mantle tomography, and in software design, education and outreach, statistics and applied mathematics.The resolving power of global seismic-tomographic wave speed models in the mid- to deep mantle remains limited due the lack of seismic data from the oceans, hampering a more detailed exploration and interpretative understanding of Earth's uncharted interior. Deploying and recovering ocean-bottom devices is technically challenging and expensive. Low-cost, freely-floating, autonomous hydrophone arrays are enhancing the resolving power of P-wave tomography. With an international consortium, floats have been deployed in French Polynesia to record teleseismic wave arrivals over the next five years. In this first two-year phase of the project, the data recovered in near-real time will be collected, quality-controlled, archived, documented and publicly disseminated. The first-arrival travel-time anomalies will be analyzed with respect to one-dimensional velocity reference models with an eye towards creating a curated high-quality data set suitable for regional tomographic inversions. The seismological analysis of travel-time anomalies from the oceanic array will be compared with new results obtained from mantle transition-zone receiver functions constructed from records collected at nearby land stations. The aperture of the array is a substantial improvement over the handful of stations in the global networks, hence the results of both lines of study will represent concrete improvements on understanding of the mantle. Mantle tomography is limited by data availability; sampling is poorest in the southern hemisphere, which is home to a number of mantle plumes that drive the heat engine that cools deep Earth. The connections of hot spots to mantle structure at great depth remain uncertain. The new data analyzed during this project will be used to frame and ultimately answer major questions on present-day mantle dynamics and on the thermal evolution of Earth.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.