Basal icequakes during changing subglacial water pressures beneath Gornergletscher, Switzerland
Basal icequakes during changing subglacial water pressures beneath Gornergletscher, Switzerland
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DOI：
10.3189/002214308785837110
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发表时间：
2008
影响因子：
3.4
通讯作者：
F. Walter;N. Deichmann;M. Funk
中科院分区：
文献类型：
--
作者：
F. Walter;N. Deichmann;M. Funk
摘要利用与冰层直接接触的三分量地震仪组成的密集网络，在2004年和2006年夏季调查了瑞士Gornergletscher的地震活动，当时冰下水压变化很大。这些压力变化是由于融化水输入的日循环，以及附近边缘冰坝湖泊Gornersee的冰下排水。每天记录的地震信号多达数千个。虽然大多数冰川是由于地表裂缝的开口，但大约有200次冰川事件被可靠地定位在靠近冰川床的地方。这些基本事件往往成群性地发生，并且具有脉冲第一到达的信号。同时，测量了基本水压和冰面流速，以捕捉湖泊排水对冰下水文系统和冰流动力学的影响。与我们的预期相反，我们没有观察到随着湖泊排空，基本冰川活动增加，从而在几天内提高了接近漂浮水平的冰下水压。事实上，基本冰震通常是在早上记录的，此时基础水压要么很低，要么下降。在湖泊排水引起的高压期，没有观测到基本的冰川。此外，GPS测量表明，在基本地震活动期间，冰川表面正在下降。这些观察结果使我们得出结论，这种冰川与冰川在冰床上滑动的日变化有关。
Abstract Using dense networks of three-component seismometers installed in direct contact with the ice, the seismic activity of Gornergletscher, Switzerland, was investigated during the summers of 2004 and 2006, as subglacial water pressures varied drastically. These pressure variations are due to the diurnal cycle of meltwater input as well as the subglacial drainage of Gornersee, a nearby marginal ice-dammed lake. Up to several thousand seismic signals per day were recorded. Whereas most icequakes are due to surface crevasse openings, about 200 events have been reliably located close to the glacier bed. These basal events tend to occur in clusters and have signals with impulsive first arrivals. At the same time, basal water pressures and ice-surface velocities were measured to capture the impact of the lake drainage on the subglacial hydrological system and the ice-flow dynamics. Contrary to our expectations, we did not observe an increase of basal icequake activity as the lake emptied, thereby raising the subglacial water pressures close to the flotation level for several days. In fact, the basal icequakes were usually recorded during the morning hours, when the basal water pressure was either low or decreasing. During the high-pressure period caused by the drainage of the lake, no basal icequakes were observed. Furthermore, GPS measurements showed that the glacier surface was lowering during the basal seismic activity. These observations lead us to conclude that such icequakes are connected to the diurnal variation in glacier sliding across the glacier bed.