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，海平面上升的速度是一个主要的未知数。这被认为是受到质量从冰盖和冰川转移到海洋的重大影响，既作为融化的水径流，也作为冰山。冰川滑动的时空变异性决定了冰团最具动力的行为。在冰川表面测量的微震活动包含了关于基础运动的信息，包括滑动速度和位移、滑动区域和基础剪切应力。然而，从地震活动中提取这一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，广泛用于表征地壳断层滑动的地震学方法将继续不能充分利用来揭示现代冰块下的滑动特征。PI提出了局部诱发冰川快速滑动，直接在床上测量，并研究这种滑动的地震表达。这项工作只能在挪威的斯瓦蒂森冰帽完成，那里的冰层下岩石隧道提供了通往厚厚冰川底部的不同寻常的通道。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岩运动和水压力，可以局部测量基床上的剪切力，可以在冰下测量地震活动性，可以在扰动10-50平方米河床的抽水试验中增加基水压力。将进行两组测量，并在次年重复进行。在4月份冰川表面显著融化之前，将进行抽水试验，使基本水压高于冰盖压力，从而导致局部滑动。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中的隧道。从地表地震活动推断的震源位置、滑动运动学和基本剪应力将与冰下直接测量和冰下收集的地震数据进行比较，以测试和校准地震反演的方法。在5月和6月期间，将监测和解释自然地震活动，因为输入到河床的波动水会导致水压和储水量的变化。结果将有助于优化利用微震活动来研究大面积冰川床上的基底运动，并将与所有滑动冰块的研究相关，无论它们的冰床类型、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.