Assessing the Efficiency of Thermal Pressurization Using Natural Pseudotachylyte-Bearing Rocks
Assessing the Efficiency of Thermal Pressurization Using Natural Pseudotachylyte-Bearing Rocks
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DOI：
10.1029/2018gl078649
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发表时间：
2018-09-28
影响因子：
5.2
通讯作者：
Mitchell, Thomas M.
中科院分区：
文献类型：
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作者：
Brantut, Nicolas;Mitchell, Thomas M.
热加压作为动态弱化机制的效率取决于形成断层核的岩石的热和水力性质。在这里，我们评估的有效性，通过比较预测的温度上升到现场估计的基础上，含假玄武玻璃岩的热增压。我们测量水力和运输性能的一套断层岩（愈合碎裂岩，未愈合的角砾岩，和完整的母岩）从假玄武玻璃轴承Gole Larghe故障在阿达梅洛岩基（意大利），并使用它们作为输入的数值模拟的热增压。我们发现，只有使用受损的、未愈合的岩石特性，才能达到熔化温度。完整岩石的渗透率增加十倍或孔隙压缩性增加四倍才能达到熔融。我们的研究结果强调了损伤过程的重要性，这些损伤过程强烈地改变了断层岩石的性质，并在地震传播过程中动态地削弱了断层岩石的性质。在地壳深处如此快速的滑动速度预计会产生大量的热量，并融化滑动界面处的岩石。然而，这种熔融岩石在断层中没有系统的观察。人们提出了一些机制来解释这种明显的差异。一个令人信服的解释是，断层岩石孔隙中的水通过快速加压和减少断层摩擦来缓冲断层温度。这种效应已经从物理模型中预测出来，但这些预测强烈依赖于约束较差的岩石性质，并且尚未在自然界中进行测试。在这里，我们测量的关键物理特性在岩石附近的断层，经历摩擦熔化，我们测试模型预测的加压水的影响是否与熔体的存在是一致的。我们发现，只有当岩石的性质被改变，以解释地震破裂过程中可能产生的微裂缝的影响时，情况才会如此。我们的研究结果提供了约束，以改善地震模拟和突出的关键作用，断层滑动过程中的微破裂损伤。
The efficiency of thermal pressurization as a dynamic weakening mechanism relies on the thermal and hydraulic properties of the rocks forming the fault core. Here we assess the effectiveness of thermal pressurization by comparing predictions of temperature rise to field estimates based on pseudotachylyte-bearing rocks. We measure hydraulic and transport properties of a suite of fault rocks (a healed cataclasite, an unhealed breccia, and the intact parent rock) from the pseudotachylyte-bearing Gole Larghe fault in the Adamello batholith (Italy) and use them as inputs in numerical simulations of thermal pressurization. We find that the melting temperature can be reached only if damaged, unhealed rock properties are used. A tenfold increase in permeability or a fourfold increase in pore compressibility of the intact rock is required to achieve melting. Our results emphasize the importance of damage processes that strongly modify fault rock properties and dynamic weakening processes during earthquake propagation.Plain Language Summary During earthquakes, faults slide rapidly past each other, typically at several meters per second. Such fast sliding rates at great depth in the crust are expected to generate large amounts of heat and should melt the rocks at the sliding interface. However, such melted rocks are not systematically observed in faults. A number of mechanisms have been suggested to explain this apparent discrepancy. One convincing explanation is that the presence of water within the porosity of the fault rocks buffers the fault temperature by being rapidly pressurized and reducing the fault friction. This effect has been predicted from physical models, but these predictions depend strongly on poorly constrained rock properties and have not yet been tested in nature. Here we measured key physical properties in rocks adjacent to a fault that underwent frictional melting, and we test whether model predictions for the effects of pressurized water are consistent with the presence of melt. We find that it is the case only if rock properties are altered to account for the effect of microfractures that are likely created during earthquake rupture. Our results provide constrains to improve earthquake simulations and highlight the key role of microfracture damage on fault sliding processes.