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。地震波速的变化是由地球温度和成分的变化引起的。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到地表的传递方式，到地球深层与地表过程之间的相互作用，如构造板块运动和地壳变形。然而，记录地震波的地震仪的地理数据覆盖范围并不统一，这仍然是地震研究的基本限制因素。由于地球表面三分之二被海洋覆盖，在海洋中部署地震仪很困难，这些地区的仪器覆盖范围很小。因此，所有地球的三维模型都在几乎或根本无法获得信息的区域标出空白点。一种自主的机器人地震传感器已经开发出来，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一移动传感器车队的数据，以成像地球地幔中的小规模结构，并提供对地球热史的更好了解。在该项目期间，将开发一款采用浮动的智能手机应用程序，并在K-12推广项目中使用。该项目支持对学生进行海洋地质学和地球物理学、地幔层析成像以及软件设计、教育和推广、统计学和应用数学方面的培训。由于缺乏来自海洋的地震数据，全球地震-层析成像波速模型在中至深地幔的分辨率仍然有限，阻碍了对地球未知内部的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，成本也很高。低成本、自由浮动、自主的水听器阵列正在增强P波层析成像的分辨率。与一个国际财团合作，在法属波利尼西亚部署了彩车，以记录未来五年远程地震波的到达情况。在该项目的第一个两年阶段，将收集、质量控制、存档、记录和公开传播近乎实时恢复的数据。将针对一维速度参考模型分析第一到达旅行时间异常，以期创建适合于区域层析成像反演的精选高质量数据集。来自海洋阵列的旅行时间异常的地震学分析将与根据附近陆面站收集的记录建立的地幔过渡区接收器函数所获得的新结果进行比较。与全球网络中的少数几个站相比，该阵列的口径有了很大的改进，因此，这两条线的研究结果都将代表着对地幔了解的具体改进。地幔层析成像受到数据可获得性的限制；南半球的采样最差，那里有许多地幔热柱，驱动着冷却地球深处的热机。热点与深部地幔结构之间的联系仍不确定。在这个项目中分析的新数据将被用来框架和最终回答关于当今地幔动力学和地球热演化的主要问题。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。

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.