Earth and Planetary Sciences, McGill University, Montréal, QC, H3A 0E8, Canada.
Dipartimento di Geoscienze, Università degli Studi di Padova, Via Gradenigo 6, 35131, Padova, Italy.
Nat Commun. 2019 Jan 18;10(1):320. doi: 10.1038/s41467-018-08238-y.
During earthquake propagation, geologic faults lose their strength, then strengthen as slip slows and stops. Many slip-weakening mechanisms are active in the upper-mid crust, but healing is not always well-explained. Here we show that the distinct structure and rate-dependent properties of amorphous nanopowder (not silica gel) formed by grinding of quartz can cause extreme strength loss at high slip rates. We propose a weakening and related strengthening mechanism that may act throughout the quartz-bearing continental crust. The action of two slip rate-dependent mechanisms offers a plausible explanation for the observed weakening: thermally-enhanced plasticity, and particulate flow aided by hydrodynamic lubrication. Rapid cooling of the particles causes rapid strengthening, and inter-particle bonds form at longer timescales. The timescales of these two processes correspond to the timescales of post-seismic healing observed in earthquakes. In natural faults, this nanopowder crystallizes to quartz over 10s-100s years, leaving veins which may be indistinguishable from common quartz veins.
在地震传播过程中，地质断层会失去强度，然后随着滑动的减缓而增强。在上地壳中部有许多滑动减弱的机制在起作用，但愈合并不总是能得到很好的解释。在这里，我们表明，由石英研磨形成的非晶纳米粉末（不是硅胶）的独特结构和速率相关特性，会在高滑动速率下导致强度急剧下降。我们提出了一种弱化和相关强化机制，这种机制可能在整个含石英的大陆地壳中起作用。两种滑动速率相关机制的作用为观察到的弱化提供了一个合理的解释：热增强塑性和由流体动力润滑辅助的颗粒流。颗粒的快速冷却会导致快速增强，而在更长的时间尺度上会形成颗粒间的键。这两个过程的时间尺度与地震中观察到的余震愈合的时间尺度相对应。在天然断层中，这种纳米粉末会在 10 秒到 100 秒的时间内结晶成石英，留下的脉体可能与常见的石英脉体无法区分。
