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The conundrums of the postglacial tectonic response of the Fennoscandian and Canadian Shields
Earth-Science Reviews ( IF 12.1 ) Pub Date : 2022-08-05 , DOI: 10.1016/j.earscirev.2022.104146
Hilmar Bungum , Olav Eldholm

A review of the early Holocene paleoseismicity in areas covered by huge ice sheets in the interior of Fennoscandia and North America shows that observational data and numerical modelling are consistent with a Glacial Isostatic Adjustment response to ice removal from thick old lithosphere during the last deglaciation. We primarily relate this climate-earthquake relationship to the combined effects of the state of the lithosphere and upper asthenosphere, mainly temperature, rheology and stress, and the state and trend of the climate. The changing ice load modulates the viscoelastic Earth response and the effective stress in such a way that it may cause crustal earthquake ruptures and earthquakes by positive augmentation of pre-existing sources of stress, potentially reactivating old structural features, i.e., inheritance and rejuvenation. The review also introduces issues related to modelling methods and assumptions, such as using realistic ice loads in space and time and appropriate lateral and vertical models of structure, composition and physical properties of the crust and upper mantle. With such caveats in mind, the difference in postglacial tectonic response in North America and Fennoscandia is yet not satisfactorily understood. However, differences in stress augmentation, a greater and longer lasting ice load over a lower relief bedrock, and potential release of stress at greater depth may be specific to North America. Also, while Archean crust characterizes most of the Canadian Shield, almost all of the Fennoscandian paleoseismicity is found in Proterozoic terrains, between the Caledonides to the west and the Archean shield to the northeast. Moreover, the plate boundary configuration yields a variable intraplate ridge-push trend not yet properly accounted for in modelling. In Fennoscandia, there is a clear spatial relationship between rebound, earthquakes and old structures in the Lapland Fault Province and beyond. While the main seismic activity earlier was assumed to have occurred during ~11.5–8.2 ka, there is now increasing evidence also for mid- and late-Holocene ruptures and for fault segmentation instead of previously assumed whole-scarp ruptures, which yielded magnitude estimates up to M ~ 8.2. However, the rupture dates and magnitudes of most postglacial events in Fennoscandia are still uncertain, and even more so in North America.



中文翻译:

Fennoscandian 和 Canadian Shields 冰后构造反应的难题

对芬诺斯坎迪亚和北美内部巨大冰盖覆盖区域的早期全新世古地震活动的回顾表明,观测数据和数值模拟与最后一次冰消期间厚旧岩石圈冰去除的冰川等静压调整响应一致。我们主要将这种气候-地震关系与岩石圈和软流圈上部状态的综合影响联系起来,主要是温度、流变学和应力,以及气候的状态和趋势。不断变化的冰负荷调节粘弹性地球响应和有效应力,使其可能通过积极增加预先存在的应力源而导致地壳地震破裂和地震,从而可能重新激活旧的结构特征,即继承和复兴。该评论还介绍了与建模方法和假设相关的问题,例如在空间和时间上使用现实的冰载荷以及适当的横向和垂直模型,地壳和上地幔的结构、成分和物理特性。考虑到这些警告,冰后期的差异北美和芬诺斯坎迪亚的构造反应尚未得到令人满意的理解。然而,应力增加的差异、较低地势基岩上更大和更持久的冰载荷以及更深的潜在应力释放可能是北美特有的。此外,虽然太古宙地壳是加拿大地盾的大部分特征,但几乎所有的芬诺斯坎德古地震活动都发现于元古代地形,位于西部的加里多尼德斯山脉和东北部的太古宙地盾之间。此外,板块边界配置产生了一个可变的板内脊推趋势,尚未在建模中正确考虑。在 Fennoscandia,反弹、地震和拉普兰断层省及更远地区的旧结构之间存在明显的空间关系。虽然早期的主要地震活动被假定发生在~11.5-8.2 ka 期间,但现在有越来越多的证据表明中、晚全新世破裂和断层分割,而不是以前假设的整个陡坡破裂,这产生了向上的震级估计至 M ~ 8.2。然而,芬诺斯坎迪亚的大多数冰后事件的破裂日期和幅度仍然不确定,在北美更是如此。

更新日期:2022-08-05
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