Stress-breakdown time and slip-weakening distance inferred from slip-velocity functions on earthquake faults
Stress-breakdown time and slip-weakening distance inferred from slip-velocity functions on earthquake faults
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DOI：
10.1785/0120020082
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发表时间：
2003-02-01
影响因子：
3
通讯作者：
Yagi, Y
中科院分区：
文献类型：
--
作者：
Mikumo, T;Olsen, KB;Yagi, Y
我们使用一种新的方法来估计地震断层上的临界滑动弱化距离，该方法与断裂能或辐射地震能量的估计无关。这种方法是从断层上每一点的剪应力、滑移和滑动速度的时间历史中找到剪应力破裂时间T-b、滑移速度峰值时间T-Pv和滑移弱化距离De之间的物理关系，这些关系可以通过使用简单的滑移弱化摩擦定律进行动态破裂计算得到。用有限差分格式对位于半空间中的垂直断层和更接近实际的水平层状结构上的动态剪切裂纹自发扩展或以固定破裂速度扩展进行了数值计算。结果表明，即使在应力降分布不均匀的情况下，断层的T-PV与T-b也有很好的相关性，但在靠近强屏障和断层边缘的位置除外。我们还研究了不同类型的滑移弱化行为之间的关系。我们将该方法应用于日本西部最近发生的两次走滑地震，2000年的鸟取县地震和1995年的神户地震。我们对由强震和远震记录的运动波形反演得到的垂直断层上的滑动速度函数，从破裂到达时间T-r到峰值滑动速度T-Pv进行积分，然后对在T-Pv获得的滑动进行了动态计算的误差修正。结果表明，这两条地震断层在0.05~0.5赫兹频段估计的滑移弱化距离在40~90厘米之间。然而，如果我们考虑到观测波形的有限频率分辨率、运动学反演得到的滑移速度函数中可能存在的时间误差以及滑移弱化行为的不确定性，上述估计可能位于最小可分辨极限与其实际值的上限之间。估计的D-c值似乎不一定指示断层较浅部分的较大值和较深部分的较小值，而是一种似乎依赖于局部最大滑动的空间不均匀分布。这种可能的依赖性可以用断层的摩擦特性来解释，除了应力不均匀外，还可以解释断层的粗糙程度或泥层厚度。
We estimate the critical slip-weakening distance on earthquake faults by using a new approach, which is independent of the estimate of fracture energy or radiated seismic energy. The approach is to find a physically based relation between the breakdown time of shear stress T-b, the time of peak slip-velocity T-pv, and the slip-weakening distance De, from the time histories of shear stress, slip, and slip velocity at each point on the fault, which can be obtained from dynamic rupture calculations using a simple slip-weakening friction law. Numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 31) half-space and a more realistic horizontally layered structure, with finite-difference schemes. The results show that T-pv is well correlated with T-b for faults even with a heterogeneous stress-drop distribution, except at locations near strong barriers and the fault edges. We also investigate this relation for different types of slip-weakening behavior. We have applied the method to two recent, strike-slip earthquakes in western Japan, the 2000 Tottori and the 1995 Kobe events. We integrated the slip-velocity functions on the vertical fault obtained from kinematic waveform inversion of strong-motion and teleseismic records from the arrival time of rupture T-r to the time of the peak-slip velocity T-pv and we then corrected the slip obtained at T-pv for the errors expected from the dynamic calculations. It was found that the slip-weakening distance De estimated in the frequency window between 0.05 and 0.5 Hz ranges between 40 and 90 cm on the two earthquake faults. However, if we consider the limited frequency resolution of the observed waveforms, probable time errors in the slip-velocity functions obtained from kinematic inversion, and the uncertainty of the slip-weakening behavior, the above estimates may be those located between the minimum resolvable limit and the upper bound of their real values. The estimated D-c values do not necessarily seem to indicate larger values in the shallower part and smaller values in the deeper part of the fault, but rather a spatially heterogeneous distribution that appears to be dependent on the local maximum slip. This possible dependence might be interpreted by the frictional properties of the fault such as the degree of roughness or the thickness of gouge layers, in addition to stress heterogeneities.