A physical model of the effect of a shallow weak layer on strong ground motion for strike-slip ruptures
A physical model of the effect of a shallow weak layer on strong ground motion for strike-slip ruptures
复制标题
浅层软弱层对走滑破裂强地震动影响的物理模型
DOI：
10.2172/776519
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发表时间：
1998
影响因子：
3
通讯作者：
A. Anooshehpoor
中科院分区：
文献类型：
--
作者：
J. Brune;A. Anooshehpoor
我们报告的结果泡沫橡胶模拟的影响，浅弱层对地面运动的走滑破裂。走滑型地震的强地面运动的计算机模拟涉及到对断层浅部沿着滑动性质的一些任意假设（例如，沿着断层面的上部2公里将滑动沿着固定为零），以便匹配某些强运动加速度记录。大多数地震强震地面运动的模拟研究都采用了所谓的运动位错模型。在运动学建模中，给出了断层滑动的时间函数，并计算了层状介质的响应。不幸的是，除非事先知道介质的真实性质及其运动，否则不能保证模型和规定的滑移在物理上是合理的。我们有充分的理由相信，在许多情况下，断层带上部沿着几公里处的断层很弱，可能无法维持地震期间高动态能量释放所需的高水平剪切应变。断层作用的物理模型，与数值或数学模型不同，保证遵守静态和动态力学定律。泡沫橡胶建模研究已在许多出版物中报道。本文的目的是提出一个浅部软弱层的物理模拟结果，以验证假设长的上升时间和减少的高频脉冲的断层浅部的滑动的物理基础。看来，沿走滑断层沿着的2公里深的弱带确实可以减少从浅层滑动辐射的高频能量，并且这种效果可以通过在长得多的上升时间滑动的开始处叠加小振幅、短上升时间脉冲来最好地表示。通过在泡沫橡胶模型中插入几英寸厚的弱塑料层来模拟弱区。对于15 cm的弱区，平均脉冲减少了0.46倍。20 cm外壳减小的系数为0.11。对于30 cm的情况，它是0.045。从这些结果可以看出，弱层越厚，短上升时间的加速度脉冲就越难穿过弱层到达表面。因此，如果已知走滑断层的浅部较弱或没有储存剪切应力，这就近似地证明了减少走滑断层浅部高频辐射的合理性。
We report results of foam-rubber modeling of the effect of a shallow weak layer on ground motion from strike-slip ruptures. Computer modeling of strong ground motion from strike-slip earthquakes has involved somewhat arbitrary assumptions about the nature of slip along the shallow part of the fault (e.g., fixing the slip to be zero along the upper 2 kilometers of the fault plane) in order to match certain strong motion accelerograms. Most modeling studies of earthquake strong ground motion have used what is termed kinematic dislocation modeling. In kinematic modeling the time function for slip on the fault is prescribed, and the response of the layered medium is calculated. Unfortunately, there is no guarantee that the model and the prescribed slip are physically reasonable unless the true nature of the medium and its motions are known ahead of time. There is good reason to believe that in many cases faults are weak along the upper few kilometers of the fault zone and may not be able to maintain high levels of shear strain required for high dynamic energy release during earthquakes. Physical models of faulting, as distinct from numerical or mathematical models, are guaranteed to obey static and dynamic mechanical laws. Foam-rubber modeling studies have been reported in a number of publications. The object of this paper is to present results of physical modeling using a shallow weak layer, in order to verify the physical basis for assuming a long rise time and a reduced high frequency pulse for the slip on the shallow part of faults. It appears a 2-kilometer deep, weak zone along strike-slip faults could indeed reduce the high frequency energy radiated from shallow slip, and that this effect can best be represented by superimposing a small amplitude, short rise-time pulse at the onset of a much longer rise-time slip. A weak zone was modeled by inserting weak plastic layers of a few inches in thickness into the foam rubber model. For the 15 cm weak zone the average pulse is reduced by a factor of 0.46. The factor for the 20 cm case reduction is 0.11. For the 30 cm case it is 0.045. From these results we can see that, the thicker the weak layer, the more difficult it is for a short rise-time acceleration pulse to push its way through the weak layer to the surface. This is thus an approximate justification for reducing the high frequency radiation from shallower parts of strike-slip faults if it is known that the shallow part of the fault is weak or has not stored up shear stress.