Study of Inner Core Motions using Seismic Waveform Doublets

这个项目是研究内核的时间依赖特征，包括内核的旋转，基于测量的地震波来源于波形偶线。（双重波形是发生在不同时间但几乎完全相同地点的两次地震的地震信号，因此它们的波形在记录两个事件的每个台站看起来非常相似。）这种新方法基于对波形双偶波的搜索，避免了地球中未知的横向非均质性的污染，并使研究集中在对穿越内核的双偶波信号之间的走时变化的非常精确测量的解释上。这种方法的学术价值在于，它促进了对地球最深处动态本质的认识；这对我们的星球是如何分化的，以及流体核心中对流保持的活力程度有很大的影响。通过在时间尺度上测量内核内部的变化，可以在十年或更短的时间内产生可察觉的影响，对地球总体热流和能量平衡的研究产生了影响；地磁学;重力，还有地震学。（这是与地球表面可观测特征相关的四个地球物理学科）。这项工作具有更广泛的影响，因为(a)它是研究的一个新转折，在20世纪90年代引发了数百条新闻报道；(b)任何年龄的人，即使缺乏科学训练，但只要对我们所居住的这个星球感到好奇，都很容易理解；最根本的原因是(c)内核，作为一个月球大小的物体，显然在地球内部运动，是一个迷人的物体，也是科学如何完成的好故事的背景。研究者研究走时变化的方法也对精密地震学的一般学科做出了贡献，在精确地震学中，即使是远震信号，也要注意在约10毫秒的水平上的走时变化。在俯冲带中发现新的波形偶波在地震物理学的背景下是非常有趣的，无论这些事件是在时间上紧密地一起发生还是相隔几年。

This project is to study time-dependent features of the inner core, including inner core rotation, based on measurements made on seismic waves derived from waveform doublets. (Waveform doublets are the seismic signals from two earthquakes occurring at different times but in almost exactly the same location, so that their waveforms look very similar at each station recording both events.) The new approach, based on a search for waveform doublets, avoids contamination from unknown lateral heterogeneities in the Earth and allows the research to focus on the interpretation of very precise measurements of the travel-time change between doublets signals that have traversed the inner core.The intellectual merit of this approach is that it promotes recognition of the dynamic nature of the Earth's deepest interior; and that it has implications for the big picture of how our planet differentiated, and the degree of vigor with which convection in the fluid core is maintained. By measuring changes within the inner core on a time scale that can lead to perceptible effects over a decade or less, there are consequences in the study of Earth's overall heat flow and energy balance; geomagnetism; and gravity, as well as seismology. (These are the four geophysical disciplines associated with observable features measurable at the Earth's surface).The work has broader impact because (a) it is a new twist on research that led to hundreds of news stories in the 1990s; (b) it is quite easily understandable by people of all ages who lack scientific training but who are curious about the planet on which we live; and most fundamentally because (c) the inner core, as a Moon-sized object apparently moving inside the Earth, is a fascinating object, and the background to good stories of how science is done.The investigator's methods for studying travel-time change are also a contribution within the general subject of precision seismology, in which even teleseismic signals are measured with attention to travel time changes at the level of ~ 10 milliseconds. The discovery of new waveform doublets in subduction zones is of great interest in the context of earthquake physics, whether the events occur close together in time or are separated by several years.