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Experimental Study on Near-Fault High-Frequency Strong Motion

近断层高频强运动实验研究

基本信息

批准号：
06402062
负责人：
HIRASAWA Tomowo
金额：
$ 8.7万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (A)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06402062/
关键词：
Stick-Slip Stable Sliding Asperity Brittle Fracture Microfracture 不安定すべり時間依存性

项目摘要

A stick-slip experiment is performed on a rock specimen with a pre-existing artificial fault to observe near-fault high-frequency elastic waves generated by stick-slip motion. The main results are as follows : 1) The observed near-fault high-frequency strong-motion duration is approximately proportional to the local breakdown time. 2) The highest peak acceleration observed amounts to a few tens of km/s^2, which is considered to correspond to about 1000gal in the case of natural earthquakes, when the differences is size and frequency are taken into account. Further we model the dynamic behavior of stick-slip motion observed in our laboratory experiment : A number of asperities circular in shape are assumed to distribute on a given fault surface. Each asperity on the fault is to be ruptured after the arrival of the macroscopic rupture front. We consider, however, that there exists some time lag between the arrival time of rupture front and the rupture initiation of the asperity. It is assumed that the time lags for individual asperities obey a certain probability density function. The synthesized strong motions reproduce well the characteristics of the observed strong motions.The above result based on the model implies that high-frequency strong motions observed during unstable sliding on a pre-existing fault are generated mainly by brittle fracture of asperities on the fault surfaces. It follows from this that acoustic emission (AE) due to brittle fracture of asperities should be observed even in the case of macroscopically stable sliding on a pre-existing fault. To examine this, an experiment of stable sliding is performed on a rock specimen with a pre-existing fault. A number of AEs are observed during macroscopically stable sliding to confirm our theoretical expectation. It is further found that the number of AEs per unit slip distance and the average magnitude of AEs are decreased with an increase in macroscopic sliding-speed.

在人工断层存在的岩石试样上进行了粘滑实验，观察了近断层粘滑运动产生的高频弹性波。主要结果如下：1)观测到的近断层高频强震持续时间与局部击穿时间近似成正比。2)观测到的最高加速度峰值可达几十km/s^2，考虑到自然地震的大小和频率差异，可以认为这相当于1000加仑左右。此外，我们对实验室实验中观察到的粘滑运动的动态行为进行了建模：假设在给定的断层表面上分布着许多圆形的凸起。断层上的每一个凹凸面都是在宏观破裂前缘到达后被破裂的。然而，我们认为在破裂锋到达时间和粗糙体破裂起始时间之间存在一定的时间滞后。假设单个凸点的时间滞后服从一定的概率密度函数。合成的强运动较好地再现了观测到的强运动特征。基于该模型的上述结果表明，在已存在断层的不稳定滑动过程中观测到的高频强运动主要是由断层表面的粗糙体脆性断裂产生的。由此可见，即使在已有断层上发生宏观稳定滑动的情况下，也应观察到岩石脆性断裂引起的声发射。为了验证这一点，在一个预先存在断层的岩石样品上进行了稳定滑动实验。在宏观稳定滑动过程中观察到许多ae，以证实我们的理论期望。随着宏观滑移速度的增加，单位滑移距离的ae数和ae的平均量级减小。