Effects of changes in temperature and fluid pressure on dynamic earthquake rupture in a thermo-poroelastic medium

从理论上研究了地震动力破裂的热水力效应。首先，推导了多孔弹性介质的控制方程组，并在此基础上进行了数值计算。温度、流体压力和断层滑动变化之间的非线性反馈在破裂动力学中起着重要作用。例如，由于这些反馈，发现断层滑动的持续时间比弹性介质中的经典格里菲斯裂缝模型所期望的要长；升温断裂带厚度越大，与Griffith裂纹模型解的偏差越大。反馈还会产生滑移弱化行为和逐渐发生滑移。从热断裂带流出的流体速率越大，滑移弱化距离越大。在我们的模拟中还发现了一个趋势，即较小规模的事件具有较小的应力降，这与一些地震观测相一致；介质渗透率越小，小、大事件的应力降差越大。这是因为持续的断层滑动倾向于提高流体压力。本文的模拟结果表明，由于热水力效应的影响，小地震和大地震之间的尺度关系相当复杂。

We theoretically study thermo-hydraulic effects on dynamic earthquake rupture. First, the system of governing equations is derived assuming a thereto-poroelastic medium, and then numerical calculations are carried out based on these equations. Non-linear feedbacks among changes in temperature, fluid pressure and fault slip are shown to play important roles in the rupture dynamics. For example, the duration of fault slip is found to be longer than expected from the classical Griffith crack model located in an elastic medium because of these feedbacks ; the deviation from the solution for the Griffith crack model is larger when the thickness of heated fault zone is larger. The feedbacks also produce slip-weakening behavior and gradual slip onset. Slip-weakening distance is shown to be larger when the rate of fluid outflow from the heated fault zone is larger. A tendency is also found in our simulations that smaller-size events have smaller stress drops, which is consistent with some seismological observations ; the difference in the stress drop between small-and large-size events is larger when the permeability of the medium is smaller. This occurs because ongoing fault slip tends to raise fluid pressure. Our simulations in this paper suggest that scaling relation between small-and large-size earthquakes are rather complicated because of thermo-hydraulic effects.