Seismic studies of glaciers yield insights into spatio-temporal processes within and beneath glaciers on scales relevant to flow and deformation of the ice. These methods enable direct monitoring of the bed in ways that complement other geophysical techniques, such as geodetic or ground penetrating radar observations. In this work, we report on the analysis of passive seismic data collected from the interior of the North East Greenland Ice Stream, the Greenland ice sheet's largest outlet glacier. We record thousands of basal earthquakes, many of which repeat with nearly identical waveforms. We also record many long-duration glacial tremor episodes that migrate across the seismic network with slow velocities (e.g. ~4–12 m s−1). Analysis of the basal earthquakes indicates a transition between times of individual event activity and times of tremor activity. We suggest that both processes are produced by shear slip at localized asperities along the bed. The transition between discrete and quasi-continuous slipping modes may be driven by pore-water pressure transients or heterogeneous strain accumulation in the ice due to strength contrasts of the underlying till.

中文翻译：

---

东北格陵兰冰流的基底地震活动

对冰川的地震研究可以在与冰的流动和变形相关的尺度上深入了解冰川内部和之下的时空过程。这些方法能够以补充其他地球物理技术的方式直接监测床层，例如大地测量或探地雷达观测。在这项工作中，我们报告了对从格陵兰冰盖最大的出口冰川东北格陵兰冰流内部收集的被动地震数据的分析。我们记录了数千次基础地震，其中许多以几乎相同的波形重复。我们还记录了许多以慢速（例如~4-12 ms）在地震网络中迁移的长期冰川震颤事件-1）。对基础地震的分析表明，单个事件活动的时间和震颤活动的时间之间存在过渡。我们建议这两个过程都是由沿床的局部粗糙处的剪切滑移产生的。离散滑移模式和准连续滑移模式之间的转变可能是由孔隙水压力瞬变或冰中由于下伏冰碛的强度对比引起的异质应变积累驱动的。