Glacier Seismicity and High Resolution Motion Records: Relation to Glacier Erosion

这是一项大型山地冰川基底过程的多学科研究。冰川是最有效的侵蚀因素之一。有迹象表明，冰川的基底运动与侵蚀速率直接（也许是线性）相关。然而，无论是在模型中还是在观测中，基础运动都很难评估。最近在阿拉斯加白令海峡冰川附近部署的地震仪提供了一个前所未有的机会，可以用现代宽带地震学监测基础过程。这些地震仪的数据被用来寻找冰川起源的事件，特别是基底来源。这些数据由五个连续记录GPS的冰川站和一个冰内地震仪补充。GPS正在记录冰速的三维时间序列，这将与地震记录相关联。全球定位系统在白令海峡冰川主干的平衡线下方排成一列，白令海峡冰川从巴格利冰谷流出。冰内地震仪与GPS站位于GPS阵列的中心。这个传感器被冻结在冰川表面，在一个几米深的钻孔中，用蒸汽钻钻出来。利用GPS阵列，该实验旨在检测离散滑动块、整个床滑动事件或由于基底空洞的增长而增加的冰层应力是否会导致冰川地震事件。这些机制中的每一种都可能导致不同的基底侵蚀机制。此外，结合地震和冰速数据可以观测冰川采石。宽频地震仪还可以确定地层中流体的作用，可能表现为谐波震动。预期的结果将是一个强有力的新数据记录，可用于导出改进的基础运动模型。地震数据来自2005年夏季部署的陡（圣埃利亚斯侵蚀/构造项目，由大陆动力学资助）地震阵列，该阵列用IRIS/ pascal地震网络包围了白令冰川。STEEP的基本重点是探索侵蚀与构造过程之间的联系，并建立了地震台网来研究圣埃利亚斯的构造。通过分析该网络内的冰川地震活动性，冰川地震研究利用了地震数据的新结果。从科学上讲，拟议工作的更广泛影响是通过其与大型多学科陡陡活动的直接联系。这些项目之间的协同作用是巨大的，因为了解冰川的基本过程是必不可少的。地震数据建立了一个高质量的数据集，这是冰川学中前所未有的，并得到了GPS数据的加强。该项目由地球物理学和EAR地貌学和土地利用动力学项目资助。

This is a multi-disciplinary study of basal processes on a large mountain glacier. Glaciers are among the most effective agents of erosion. There are indications that glacier basal motion is directly (maybe linearly) related to erosion rates. Yet, basal motion is difficult to assess, in models as well as from observations. A recent deployment of seismometers near the Bering Glacier, Alaska, is offering an unprecedented opportunity to monitor basal processes with modern broadband seismology. Data from these seismometers is being used to look for events of glacial origin, and in particular basal sources. These data are supplemented by five glacier stations of continuously recording GPS and an in-ice seismometer. The GPS are recording an ice velocity timeseries in 3-d that will be correlated with the seismic records. The GPS are laid out in an array just below the equilibrium line on the main trunk of the Bering Glacier where it drains from the Bagley Ice Valley. The in-ice seismometer is co-located with the GPS station at the center of the GPS array. This sensor is frozen into the surface of the glacier, in a borehole several meters deep, made using a steam drill. With the GPS laid out in an array, the experiment is designed to detect whether discrete slip patches, whole bed sliding events, or increasing ice-bed stresses due to the growth of basal cavities lead to glacial seismic events. Each of these mechanisms may contribute to different mechanisms of erosion at the base. Moreover, the combined seismic and ice velocity data may allow observation of glacial quarrying. Broadband seismometers also allow some determination of the role of fluids at the bed, possibly manifest as harmonic tremor. The expected outcome will be a powerful new data record that may be used to derive improved models of basal motion.The seismic data come from the summer 2005 deployment of the STEEP (St. Elias Erosion/tectonics Project, funded by Continental Dynamics) seismic array, which has surrounded the Bering Glacier with an IRIS/PASSCAL seismic network. The basic focus of STEEP is to explore the links between erosion and tectonic processes, and the seismic network was built to study tectonics in the St. Elias. By analyzing glacier seismicity within this network, the glacier seismic study is leveraging new results from the seismic data. Scientifically, the broader impacts of the proposed work are through its direct link to the large multi-disciplinary STEEP activity. The synergies between these projects are large, because an understanding of glacier basal processes is essential. The seismic data establishes a high quality data set that is unprecedented in glaciology and that is enhanced by the GPS data. This project is funded by Geophysics and the EAR Geomorphology and Land-Use Dynamics Program.