孕震过程中孔隙压及地下水位变化的数值模拟

NUMERICAL SIMULATION OF PORE PRESSURE AND GROUND WATER LEVEL VARIATION IN EARTHQUAKE PREPARATION

地震孕育过程中孕震区内务点的应力应变都将发生变化,介质的物性参数也将改变,因此孔隙压和地下水位随之改变。本文在研究孕震过程中包括扩容和断层蠕变效应在内的应力应变场的基础上,根据应力场与孔隙压场的耦合方程,把孔隙压场随应力场的变化定量地计算出来。计算结果表明,孕震过程中孔隙压的变化与应力场变化的强弱及介质的渗透性能等因素相关。孕震过程中孔隙压的极值区最初集中在断层端部,而后随着断层的蠕动向闭锁段中部发展。孕震过程后期,震源区表现为扩容区并且孔隙压强以负压为主,此结果显示着震源区的地下水位以下降为主,从一定程度上解释了震前地下水位的异常变化,而地下水的流动有助于理解水氡、水化学和水温等前兆的物理机制。

The paper analysed stress and strain field including the effect of rock dilatancy and fault creeping in earthquake preparation, according to coupling equation of stress and pore pressure field, the pore pressure field variation along with stress field can be calculated. The results showd that the variation of pore pressure are related to intensity of stress variation and capacity of medium osmosis. First extremum area of pore pressure concentrated at fault extreme, then turned to middle of blocking part according to fault creeping in earthquake preparation. In the later period of earthquake preparation, the source was the dilatant area as well as pore pressure in most area was negative, which can explain why the ground water level changed abnormally before earthquakes. The ground water flow can make us easier to understand the mechanism of occurred anomlies, such as water Radon, water chemistry and water temperature and so on.