Not all Icequakes are Created Equal: Basal Icequakes Suggest Diverse Bed Deformation Mechanisms at Rutford Ice Stream, West Antarctica
Not all Icequakes are Created Equal: Basal Icequakes Suggest Diverse Bed Deformation Mechanisms at Rutford Ice Stream, West Antarctica
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并非所有冰震都是一样的：基底冰震表明南极洲西部拉特福德冰流的床变形机制多种多样
DOI：
10.1029/2020jf006001
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Lee, Ian
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文献类型：
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作者：
Kufner, Sofia‐Katerina;Brisbourne, Alex M.;Smith, Andrew M.;Hudson, Thomas S.;Murray, Tavi;Schlegel, Rebecca;Kendall, John M.;Anandakrishnan, Sridhar;Lee, Ian
由冰川在其床上滑动引起的微震活动可以用来表征冰床界面的摩擦特性，这是控制冰流流动的关键参数。我们利用自然发生的地震活动来监测南极洲西部Rutford冰流的时空变化的床层性质。我们利用位于接地线上游约40公里处的35个台站地震台网90天的记录，定位了23万次当地震级为- 2.0至- 0.3的微地震。这些事件只发生在冰床界面附近，并主要表明流动-平行粘滑。它们大多位于一个解释为坚硬的区域内，以及沿着超大尺度冰川线的可能较硬的部分。在这些区域内，微地震发生在空间上（<100米半径）和时间上（主要是1-5天的活动）有限的事件群（多达4000次事件），随着时间的推移，这些事件的震级呈现先增加后减少的趋势。这可能表明一旦活动启动就会触发事件。虽然海潮调节了表面冰流速度，但我们观察到总体事件频率随时间的周期性变化很小，并得出结论，含水量，床地形和刚度是控制微震活动性的主要因素。基于不同的破裂机制和时空特征，我们认为事件群与三种末端成员类型的床变形有关：(1)小尺度床粗糙度的持续形成和地震破坏，(2)犁削碎屑，以及(3)地貌形成期间或基岩露头的流动-倾斜变形。这表明在冰川滑动过程中同时活跃的多个过程可以适应粘滑行为，并且床层不断重组。
Microseismicity, induced by the sliding of a glacier over its bed, can be used to characterize frictional properties of the ice‐bed interface, which are a key parameter controlling ice stream flow. We use naturally occurring seismicity to monitor spatiotemporally varying bed properties at Rutford Ice Stream, West Antarctica. We locate 230,000 micro‐earthquakes with local magnitudes from −2.0 to −0.3 using 90 days of recordings from a 35‐station seismic network located ∼40 km upstream of the grounding line. Events exclusively occur near the ice‐bed interface and indicate predominantly flow‐parallel stick‐slip. They mostly lie within a region of interpreted stiff till and along the likely stiffer part of mega‐scale glacial lineations. Within these regions, micro‐earthquakes occur in spatially (<100 m radius) and temporally (mostly 1–5 days activity) restricted event‐clusters (up to 4,000 events), which exhibit an increase, followed by a decrease, in event magnitude with time. This may indicate event triggering once activity is initiated. Although ocean tides modulate the surface ice flow velocity, we observe little periodic variation in overall event frequency over time and conclude that water content, bed topography and stiffness are the major factors controlling microseismicity. Based on variable rupture mechanisms and spatiotemporal characteristics, we suggest the event‐clusters relate to three end‐member types of bed deformation: (1) continuous creation and seismogenic destruction of small‐scale bed‐roughness, (2) ploughed clasts, and (3) flow‐oblique deformation during landform formation or along bedrock outcrops. This indicates that multiple processes, simultaneously active during glacial sliding, can accommodate stick‐slip behavior and that the bed continuously reorganizes.