Model constraints on infiltration of surface-derived fluids deep into the brittle crust

IF 2.8 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Guy Simpson
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引用次数: 0

Abstract

Summary Downward flow of surface-derived water deep into the upper crust is investigated using two dimensional coupled hydrothermal numerical models. In the models, downward flow is driven by either topographic gradients or seismic pumping, while it is facilitated by large episodic variations in fault permeability, intended to mimic fracturing and healing on a fault over repeated seismic cycles. The models show that both forcing scenarios are equally capable of driving surface-derived fluid to the base of faults at 10 km depth in several tens of thousands of years under certain conditions. Downward flow of cold fluid occurs almost exclusively during and shortly after earthquakes, while during the remaining portion of the seismic cycle fluids remain relatively stationary while they undergo thermal relaxation (i.e., heating). Rapid downward flow is favoured by a large coseismic permeability, long permeability healing time scale, and large coseismic dilatancy or high topographic relief above the fault at the surface. However, downward fluid flow is completely inhibited if fluid pressures exceeds the hydrostatic gradient, even by modest amounts, which suggests that deep fluid infiltration is unlikely to occur in every region.
地表流体渗入脆性地壳深处的模型制约因素
摘要 利用二维耦合热液数值模型研究了地表水向地壳上部深处的下行流动。在模型中,向下流动由地形梯度或地震抽水驱动,而断层渗透率的巨大偶发性变化则促进了向下流动,其目的是模拟断层在反复地震周期中的断裂和愈合。模型显示,在特定条件下,这两种强迫情景同样能够在数万年内将地表流体驱动到 10 公里深的断层底部。冷流体向下流动几乎只发生在地震期间和地震后不久,而在地震周期的剩余时间内,流体在经历热松弛(即加热)过程中保持相对静止。同震渗透率大、渗透率愈合时间长、同震膨胀率大或地表断层上方地形起伏大,都有利于流体快速向下流动。然而,如果流体压力超过流体静力学梯度,即使是很小的量,也会完全抑制流体向下流动,这表明深层流体渗透不可能在每个区域都发生。
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来源期刊
Geophysical Journal International
Geophysical Journal International 地学-地球化学与地球物理
CiteScore
5.40
自引率
10.70%
发文量
436
审稿时长
3.3 months
期刊介绍: Geophysical Journal International publishes top quality research papers, express letters, invited review papers and book reviews on all aspects of theoretical, computational, applied and observational geophysics.
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