Feasibility of acoustic monitoring of strength drop precursory to earthquake occurrence
Feasibility of acoustic monitoring of strength drop precursory to earthquake occurrence
复制标题
地震前兆强度下降声学监测的可行性
DOI：
--
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Tetsuya Kusakabe
中科院分区：
文献类型：
--
作者：
N. Kame;K. Nagata;M. Nakatani;Tetsuya Kusakabe
在实验室研究基础上提出的速率和状态相关摩擦定律（RSF）已被广泛应用于地震粘滑循环的模拟。一个简单的弹簧滑块模型服从RSF预测的摩擦强度Φ（接触状态），是在地震发生前几年内本地化的显着下降。另一方面，最近的实验室实验通过同时测量P波透射率成功地监测了强度的历史|不|用1兆赫的传感器在摩擦界面上测量。这表明，通过声学方法监测天然断层的强度来预报地震是可能的。本文探讨了这种监测的可行性，在现场的基础上的物理RSF结合线性滑移模型（LSM）在经典的声学方法监测不完美的焊接接口。特征频率fc，在其附近|不|（或反射率）|R|）对界面强度具有良好的灵敏度，显示出与强度成正比，与真实的接触的代表尺度成反比。对于自然故障，fc估计为1至100 Hz，这在现场是可行的。的变化|不|和|R|取决于强度下降与绝对强度水平的比率，后者不受RSF模拟的约束。对于强断层和弱断层，滑动前波振幅的预期变化分别为百分之几和百分之几十，这可以通过声学方法（如地震反射勘测）检测到。
Rate- and state-dependent friction law (RSF), proposed on the basis of laboratory experiments, has been extensively applied to modeling of earthquake stick-slip cycles. A simple spring-slider model obeying RSF predicts a significant decrease of the frictional strength Φ (the state of contact) that is localized within a few years preceding the earthquake occurrence. On the other hand, recent laboratory experiments successfully monitored the history of the strength by simultaneously measuring the P-wave transmissivity |T| across the frictional interface using a 1-MHz transducer. This suggests a possibility of earthquake forecast by monitoring the strength of a natural fault by acoustic methods. The present paper explores the feasibility of such monitoring in the field on the basis of the physics of RSF combined with the linear slip model (LSM) employed in the classical acoustic methodology for monitoring an imperfectly welded interface. The characteristic frequency fc, around which |T| (or reflectivity |R|) has a good sensitivity to the interface strength, is shown to be proportional to the strength and inversely proportional to the representative scale of real contacts. For natural faults, fc is estimated to be 1 to 100 Hz, which is practicable in the field. The changes of |T| and |R| depend on the ratio of the strength drop to the absolute strength level, the latter of which is not constrained by RSF simulations. Expected changes in wave amplitude in the preslip period would be several percent for strong faults and several tens percent for weak faults, which may be detectable by acoustic methods such as seismic reflection surveys.