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在地震滑动过程中,断层动态摩擦是地壳内控制地震破裂的决定性因素。天然地震的脆性裂纹理论[1-3]使得以下观点被普遍接受:在地震断层快速滑动的过程中,断层摩擦力减弱,即所谓的滑动弱化[1]。高速断层泥实验[4-5],以及最近关于热增压[6-7]和摩擦熔化[8]的试验都支持该理论。但是,这些研究均仅针对固定的断层滑动速率。在本文中,我们的实验展示了不同滑动速率下断层物质的摩擦行为——这一模型的设置更接近天然地震的特征。实验结果表明,在断层滑动加速和减速的过程中,断层摩擦经历了增长、弱化和再增长。这种摩擦变化可能可以由低滑动速率下和更现实的滑动速率之下的速率-状态摩擦行为[9-10]来解释,但包含了不同的物理机制和不同的规模。最初的摩擦增强可能会阻碍小破裂向大地震的发展。断层滑动减速过程中的摩擦增强可能导致地震破裂呈脉冲状[11-14],并使得静态应力下降到与动态应力变化相比较低的水平[15]。
In the process of earthquake slippage, the dynamic friction of the fault is the decisive factor in controlling the earthquake rupture in the crust. The brittle fracture theory of natural earthquakes [1-3] makes it widely accepted that during the rapid sliding of seismic faults, the fault friction weakens, so-called slip weakening [1]. This theory is supported by high-speed fault mud tests [4-5], as well as the recent tests on hot-press [6-7] and friction-melting [8]. However, all of these researches only focus on the fixed fault slip rate. In this paper, our experiments show the tribological behavior of the fault material at different slip rates - the model is set closer to the characteristics of natural earthquakes. The experimental results show that fault friction experienced growth, weakening and re-growth in the process of fault slip acceleration and deceleration. This frictional change may be explained by the rate-state friction behavior at low sliding rates and more realistic sliding rates [9-10], but with different physical mechanisms and different scales. The initial increase in friction may hinder the development of small earthquakes to large earthquakes. Friction enhancement during fault slip deceleration may cause the earthquake to burst into a pulse shape [11-14] and reduce the static stress to a lower level than the dynamic stress [15].