Pre-seismic thermal anomalies have been widely reported, however, there is still no unified understanding of their causes or physical mechanisms. To clarify whether subsurface fluid convection and rock deformation directly related to seismic fault stress release can form thermal anomalies before an earthquake, we carried out thermo-hydro-mechanical (THM) coupled modeling of the Wenchuan earthquake, and considered the influence of maximum horizontal principal stress direction (MPSD) and fault dip. The results show that convective thermal flux (CT) anomalies of subsurface fluid and the deformation induced thermal flux (DT) of the rock mass caused by stress release of the seismic fault can explain the observed thermal anomalies along the fault. The calculated and observed thermal anomalies are comparable in spatial distribution, evolution, and magnitude. Specifically, for the Wenchuan earthquake, seismic fault stress release-induced CT and DT anomalies occur in the fault zone and in the adjacent hanging wall area. In the fault zone, CT and DT induced thermal anomalies were comparable, and superposition of the two was characterized by strong initial warming, followed by weaker warming and then short-term cooling. However, outside of the fault zone, CT induced thermal anomalies had much higher intensities than those induced by DT, and were characterized by band-like warming along the hanging wall of the fault. In addition, variations in the MPSD and fault dip cause the segmentation of thermal anomalies along the Wenchuan earthquake fault. From the southern to the northern segments of the fault, the intensity of thermal anomalies is significantly weakened with rotation of MPSD and an increase in fault dip. Our study provides evidence that seismic fault stress release is the cause of pre-seismic thermal anomalies; furthermore, the results indicate the CT and DT could be important physical mechanisms of pre-seismic thermal anomalies.

地震前的热异常已经被广泛报道，但是，对其成因或物理机制仍然缺乏统一的认识。为了弄清楚与地震断层应力释放直接相关的地下流体对流和岩石变形是否会在地震前形成热异常，我们对汶川地震进行了热-水-机械（THM）耦合建模，并考虑了最大水平本构的影响。应力方向（MPSD）和断层倾角。结果表明，地下流体的对流热通量（CT）异常和地震断层应力释放引起的岩体变形诱导热通量（DT）可以解释沿断层的热异常。计算和观察到的热异常在空间分布，演化，和大小。具体来说，对于汶川地震，断层带和邻近的上悬壁区域会发生由地震断层应力释放引起的CT和DT异常。在断层带，CT和DT引起的热异常是可比较的，两者的叠加特征是强烈的初始暖化，然后是较弱的暖化，然后是短期冷却。然而，在断层带之外，CT引起的热异常强度比DT引起的强度高得多，并且特征是沿着断层的悬挂壁带状升温。此外，MPSD的变化和断层倾角导致沿汶川地震断层的热异常分段。从断层的南部到北部，随着MPSD的旋转和断层倾角的增加，热异常的强度显着减弱。我们的研究提供了证据表明，地震断层应力释放是地震前热异常的原因。此外，结果表明CT和DT可能是地震前热异常的重要物理机制。