Earthquake Ruptures with Strongly Rate-Weakening Friction and Off-Fault Plasticity, Part 2: Nonplanar Faults
Earthquake Ruptures with Strongly Rate-Weakening Friction and Off-Fault Plasticity, Part 2: Nonplanar Faults
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DOI：
10.1785/0120100076
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发表时间：
2011-10-01
影响因子：
3
通讯作者：
Kozdon, Jeremy E.
中科院分区：
文献类型：
--
作者：
Dunham, Eric M.;Belanger, David;Kozdon, Jeremy E.
观测表明，断层在所有尺度上都是偏离平面性的分形面。我们研究了均方根(RMS)高度起伏为剖面长度的10(-3)到10(-2)量级的自相似断层上的动态破裂传播。我们的二维平面应变模型具有强烈的速率弱化断层摩擦和断层外的Drucker-Prager粘塑性。后一种情况会在弯管附近产生不合理的大的应力集中。我们所选择的无粘性屈服函数可以防止张应力状态，从而防止断层张开。强烈速率弱化摩擦的结果是存在一个临界背景应力水平，在该水平以上，以自愈滑移脉冲的形式自我维持的破裂传播首先成为可能。在这一水平附近，天然断层预计会运行，破裂对断层粗糙度变得极其敏感，并表现出破裂速度的大幅波动。除了最大压应力向断层的浅倾角(小于20°)外，波动与局部断层坡度呈反相关关系。这些破裂的加速和减速，加上自然出现的滑动不均匀，激发了所有波长的波，导致地面加速度谱在高频下是平坦的，与观测到的强震记录一致。
Observations demonstrate that faults are fractal surfaces with deviations from planarity at all scales. We study dynamic rupture propagation on self-similar faults having root mean square (rms) height fluctuations of order 10(-3) to 10(-2) times the profile length. Our 2D plane strain models feature strongly rate-weakening fault friction and off-fault Drucker-Prager viscoplasticity. The latter bounds otherwise unreasonably large stress concentrations in the vicinity of bends. Our choice of a cohesionless yield function prevents tensile stress states and thus fault opening. A consequence of strongly rate-weakening friction is the existence of a critical background stress level above which self-sustaining rupture propagation, in the form of self-healing slip pulses, first becomes possible. Around this level, at which natural faults are expected to operate, ruptures become extremely sensitive to fault roughness and exhibit substantial fluctuations in rupture velocity. Except for shallow inclinations of the maximum compressive stress to the fault (less than about 20 degrees), the fluctuations are anticorrelated with the local fault slope. These accelerations and decelerations of the rupture, together with naturally emerging slip heterogeneity, excite waves of all wavelengths and result in ground acceleration spectra that are flat at high frequency, consistent with observed strong motion records.