Numerical simulations of seismicity-induced fluid flow in the Tjornes Fracture Zone, Iceland
Numerical simulations of seismicity-induced fluid flow in the Tjornes Fracture Zone, Iceland
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DOI：
10.1029/2010jb007732
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发表时间：
2011-07
影响因子：
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通讯作者：
M. Lupi;S. Geiger;C. Graham
中科院分区：
文献类型：
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作者：
M. Lupi;S. Geiger;C. Graham
[1]我们使用高分辨率模拟分析了地震活跃的Tjornes断裂带(TFZ)的流体流动、孔隙压力和断层渗透率的演化，TFZ是冰岛北部的一个主要转换断裂带。我们的结果表明，TFZ具有四个不同的孔压高于静水压的区域，这与地球物理观测一致。被认为渗透率低的基底和断层，通常显示出接近岩石静压的孔压。允许断层渗透率作为有效断层正应力的函数自由变化。因此，它们会周期性地膨胀，在几分钟内释放出多余的孔压。伴随而来的是渗透率增加7个数量级以上，导致短期流体通量超过0.01m S−1。在孔隙压力消散后，随着有效断层正应力的增加，断层渗透率在2-3年内衰减到原值。这一行为与触发开关机制相一致，并可能对地震和热液活动的洋壳中的流体流动有两个重要的影响。首先，断层渗透率和孔隙压力的快速变化解释了在5.8兆瓦地震前后在TFZ Husavik镇附近的热水中观察到的类似时间尺度上的明显周期性地球化学变化。其次，我们的结果为越来越多的观测提供了另一条证据，即地壳渗透率在不断演变，热液系统中的地质过程可能受到短期和极端流动事件的主导。
[1] We use high-resolution simulations to analyze fluid flow, pore pressure, and fault permeability evolution in the seismically active Tjornes Fracture Zone (TFZ), a major transform fault zone in the North of Iceland. Our results show that the TFZ is characterized by four distinct areas where pore pressures are above hydrostatic, consistent with geophysical observations. Basement and faults, which are assumed to have low permeabilities, often display pore pressures close to lithostatic. Fault permeabilities are allowed to vary freely as a function of the effective fault normal stress. They hence inflate periodically to release excess pore pressure in a few minutes. This is accompanied by an increase in permeability of over seven orders of magnitude and causes short-lived fluid fluxes of more than 0.01 m s−1. After pore pressures have dissipated, fault permeabilities decay back to their original values in 2 to 3 years as the effective fault normal stress increases. This behavior is consistent with a toggle switch mechanism and could have two important implications for fluid flow in seismically and hydrothermally active oceanic crust. First, the rapid changes in fault permeability and pore pressure provide an explanation for distinct cyclical geochemical changes observed on a similar timescale in thermal waters near the town of Husavik in the TFZ before and after a magnitude 5.8 Mw earthquake. Second, our results provide another line of evidence in the growing number of observations that crustal permeabilities are constantly evolving and geological processes in hydrothermal systems can be dominated by short-lived and extreme flow events.