Collaborative Research: Characterizing Brittle Failure and Fracture Propagation in Fast Ice Sliding with Dynamic Rupture Models based on Whillans Ice Stream Seismic/Geodetic Data

该项目调查了西南极冰盖中一段快速移动的被称为惠兰冰流的区域。冰流和出口冰川是冰从冰盖排放到海洋的主要途径。因此，了解冰流动力学，特别是控制冰在其底部沉积物上滑动的摩擦阻力的过程，对于预测地球冰盖将如何响应不断变化的气候至关重要。威兰冰流不是顺畅流动，而是在粘滑循环中前进：短暂的快速滑动，相当于7级地震，与更长的休止期交替出现。PI将使用最初为模拟构造地震而开发的计算机代码来模拟这些粘滑循环。通过匹配观测到的冰运动，PI将限制作用于冰流底部的摩擦过程的范围。该项目的另一个重点是冰中的脆性破裂过程，通过伴随大规模滑动事件的断层和/或破裂事件所辐射的地震波表现出来。对冰裂的了解为评估冰架对裂隙和灾难性解体的敏感性提供了基础。项目成果将被纳入推广活动(从小学到社区大学活动)以及加州州立大学数学与科学暑期学校(COSMOS)高中生计划的极地科学课程。粘滑循环的模拟将使用3D动态破裂模型，该模型同时求解地震波场和破裂过程，与冰流床上的弹性动力学材料响应和摩擦定律一致。应力和摩擦特性将改变，以实现与地面GPS和宽带地震数据以及来自WISSARD项目的钻孔地震图的一致性。这些结果将由实验室解释，直到摩擦实验，该实验将速度减弱/增强行为与温度和水分含量联系起来，并与量化粗糙床上冰流的基础阻力的相关实验相联系。将结合震源过程的力学模型，使用三维波形模拟来确定伴随滑动事件(剪切断裂与破裂)的地震活动的震源机制。这项提议不需要在南极进行实地考察。

This project investigates a rapidly moving section of the West Antarctic Ice Sheet known as the Whillans Ice Stream. Ice streams and outlet glaciers are the major pathways for ice discharge from ice sheets into the ocean. Consequently, understanding ice stream dynamics, specifically the processes controlling the frictional resistance of ice sliding on sediments at its base, is essential for predictive modeling of how Earth's ice sheets will respond to a changing climate. Rather than flowing smoothly, Whillans Ice Stream advances in stick-slip cycles: brief periods of rapid sliding, equivalent to magnitude 7 earthquakes, alternating with much longer periods of repose. The PIs will perform simulations of these stick-slip cycles using computer codes originally developed for modeling tectonic earthquakes. By matching observed ice motions, the PIs will constrain the range of frictional processes acting at the base of the ice stream. An additional focus of the project is on brittle fracture processes in ice, expressed through seismic waves radiated by faulting and/or crevassing episodes that accompany the large-scale sliding events. An understanding of ice fracture provides a basis for assessing the susceptibility of ice shelves to rifting and catastrophic disintegration. Project results will be incorporated into outreach activities (from elementary school to community college events) as well as a polar science class for the California State Summer School for Mathematics and Science (COSMOS) program for high school students.Simulations of the stick-slip cycle will employ 3D dynamic rupture models that simultaneously solve for the seismic wavefield and rupture process, consistent with elastodynamic material response and friction laws on the ice stream bed. Stresses and frictional properties will be varied to achieve consistency with surface GPS and broadband seismic data as well as borehole seismograms from the WISSARD project. The results will be interpreted using laboratory till friction experiments, which link velocity-weakening/strengthening behavior to temperature and water content, and to related experiments quantifying basal drag from ice flow over rough beds. The source mechanism of seismicity accompanying the slip events (shear faulting versus crevassing) will be determined using 3D waveform modeling in conjunction with mechanical models of the seismic source processes. This proposal does not require fieldwork in the Antarctic.