Collaborative Research: Glacier Seismicity and its relationship to basal movement

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。在估计气候变暖的影响时，一个主要的未知因素是海平面上升的速度。这被认为是受到从冰盖和冰川向海洋转移的物质的显著影响，这些物质既作为融水径流，也作为冰山。冰川滑动的时空变异性是造成冰块最具动力行为的原因。在冰川表面测量的微震活动包含有关基底运动的信息，包括滑动速度和位移、滑动面积和基底剪应力。然而，从地震活动中提取这些信息是高度不确定的，因为在冰川床上缺乏可用于指导地震反演的直接测量。如果没有这样的指导，广泛用于描述地壳断层滑动特征的地震学方法在揭示现代冰块下滑动特征方面将继续得不到充分利用。PIs建议局部诱导冰川快速滑动，直接在床上测量，并研究该滑动的地震表现。这项工作只能在挪威的斯瓦蒂森冰盖完成，在那里，冰下岩石中的隧道提供了通往厚厚的滑动冰川床的不同寻常的通道。在这个设施中，存在着重要的实验能力。可以在多个位置连续测量基底运动和水压，可以局部测量床上的剪切力，可以在冰下测量地震活动性，并且可以在对10-50 m2的床进行扰动的泵试验期间增加基础水压。明年将进行两组测量并重复进行。4月，在冰川表面明显融化之前，将进行泵试验，使基础水压高于冰覆盖压力，从而诱发局部滑动。由此产生的地震活动将在多个地点进行测量，包括冰川表面和冰川下岩石隧道。从地表地震活动性推断出的震源位置、滑动运动学和基底剪应力将与直接冰下测量结果和冰下收集的地震数据进行比较，以测试和校准地震反演方法。在5月和6月期间，将监测和解释自然地震活动，因为流入河床的波动水导致水压和储水量的变化。研究结果将有助于优化利用微地震活动来研究大面积冰川床上的基础运动，并将与所有滑动冰块的研究相关，无论其床型、大小或位置如何。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).A major unknown in the estimation of the effects of climate warming is the rate of sea level rise. This is believed to be significantly impacted by the transfer of mass from ice sheets and glaciers to the ocean, both as melt water runoff and as ice bergs. The temporal and spatial variability of glacier sliding is responsible for the most dynamic behavior of ice masses. Microseismicity measured on glacier surfaces contains information about basal movement, including slip velocity and displacement, slip areas, and basal shear stresses. However, extracting this information from seismicity is highly uncertain due to a lack of direct measurements at glacier beds that can be used to guide seismological inversions. Without such guidance, the seismological methods used extensively to characterize slip along crustal faults will continue to be underutilized for revealing characteristics of slip beneath modern ice masses.The PIs propose to locally induce rapid glacier slip, measure it directly at the bed, and study the seismic expression of that slip. This work can be accomplished only at the Svartisen Ice Cap in Norway, where tunnels in subglacial rock provide unusual access to the bed of a thick sliding glacier. At this facility, important experimental capabilities exist. Basal motion and water pressure can be measured continuously at multiple locations, shear tractions on the bed can be measured locally, seismicity can be measured subglacially, and basal water pressure can be increased during pump tests that perturb 10-50 m2 of the bed.Two sets of measurements will be made and repeated the following year. In April prior to significant melting on the glacier surface, pump tests will be conducted to bring the basal water pressure above the ice-overburden pressure, inducing local slip. Resultant seismicity will be measured at multiple locations, both at the glacier surface and in tunnels within rock beneath the glacier. Hypocenter location, slip kinematics, and basal shear stresses inferred from surface seismicity will be compared with direct subglacial measurements and with seismic data gathered subglacially to test and calibrate methods of seismological inversion. During May and June, natural seismicity will be monitored and interpreted, as fluctuating water input to the bed causes variations in water pressure and storage. Results will help optimize the use of microseismicity for studying basal movement remotely over large areas of glacier beds and will be relevant to the study of all sliding ice masses, regardless of their bed type, size, or location.