Transient and Rapid Glacial Motions, including Glacial Earthquakes

该奖项支持一个研究冰川地震的形成模式和原因的项目。冰川流动的模式一直是冰川以粘性方式流动，力平衡的重大变化发生在十年或更长的时间尺度上。最近发现的一些时间尺度更短的事件挑战了这一范式。2003年，人们发现南极洲西部的惠兰冰流在10-30分钟的时间尺度上表现出粘滑行为，冰流速度从已经很高的速度增加了30倍。在过去的一年里，由于认识到最近发现的一类50秒长的5级地震与格陵兰和东南极大型出口冰川的崩解锋面附近的力平衡变化密切相关，最小时间刻度被缩短了。由于没有足够的理论来解释这些与出口冰川相关的相对较大的地震，我们已经开始研究在一个传统上不能在低于100秒的时间尺度上产生巨大力量变化的系统中允许这种反应的物理机制。这项工作的学术价值在于，冰川的大幅度、短时间尺度变化是冰川动力学的一种重要模式，目前还没有从第一原理物理学的角度来理解这种模式。这项拟议的研究旨在解决这一认识上的差距，将冰川学、地震学和断层破裂动力学、实验室岩石物理、颗粒流、断裂力学和水文地质学等多个学科的知识联系在一起。这项工作的更广泛影响是，主要冰盖的稳定性引起了社会和普遍的科学兴趣。然而，如果不了解支配短时间尺度变化的物理过程，我们就不太可能准确地预测这些冰盖的未来及其对海平面变化的影响。该项目还将有助于青年科学家的发展和教育。

Rice 0739444This award supports a project to study the mode of formation and causes of glacial earthquakes. The paradigm for glacial flow has been that glaciers flow in a viscous manner, with major changes in the force balance occurring on the decade timescale or longer. The recent discovery of a number of even shorter timescale events has challenged this paradigm. In 2003, it was discovered that Whillans Ice Stream in West Antarctica displays stick-slip behavior on the 10-30 minute timescale, with ice stream speed increasing by a factor of 30 from already high speeds. In the past year, the minimum timescale has been pushed shorter by recognition that a class of recently discovered 50-second-long, magnitude-5 earthquakes are closely associated with changes in the force balance near the calving fronts of large outlet glaciers in both Greenland and East Antarctica. With no adequate theory existing to explain these relatively large earthquakes associated with outlet glaciers, we have begun to investigate the physical mechanisms that must be involved in allowing such a response in a system traditionally not thought capable of generating large variations in forces over timescales less than 100 seconds. The intellectual merit of the work is that large-amplitude, short-timescale variability of glaciers is an important mode of glacier dynamics that has not yet been understood from a first-principles physics perspective. The proposed research addresses this gap in understanding, tying together knowledge from numerous disciplines including glaciology, seismology and fault rupture dynamics, laboratory rock physics, granular flow, fracture mechanics, and hydrogeology. The broader impacts of the work are that there is societal as well as general scientific interest in the stability of the major ice sheets. However, without an understanding of the physical processes governing short time scale variability, it is unlikely that we will be able accurately predict the future of these ice sheets and their impact on sea level changes. The project will also contribute to the development and education of young scientists.