断裂带同震温度负异常机制分析

The coseismic temperature responses can be recognized in the borehole temperature measurements in fault zones after earthquakes. It provides a unique idea and an effective mean for basic research about the friction features and seismogenic mechanisms of fault zones. Borehole temperature measurement results show that there were both positive and negative temperature anomalies that followed the 1999 Chi-Chi, 2008 Wenchuan and 2011 Tohoku earthquakes. The positive temperature anomaly (within 5~20 m away from fault slip surfaces) has been well known because of the frictional heating that occurred during coseismic faulting. However, the negative temperature anomaly (range of 20~60 m from fault slip surfaces) still has not been noted and expressly addressed. The amplitude of the negative temperature anomaly is 1/4~1/3 of that of the positive temperature anomaly; but the range of the negative temperature anomaly are 3~4 times of that of positive anomaly. In that case, the total of energy in the negative and positive areas is basically the same. Therefore, the negative anomalies in borehole temperature measurement and their causes can no longer be ignored. After a detailed analysis of several possible mechanisms of coseismic temperature negative anomalies (i.e., differences in distribution of thermal properties, fluid migration and increase of surface free energy), it is found that only coseismic stress release is a universal mechanism that can be supported in theory, experiment and field observation. This may be the main reason for the negative temperature anomaly in fault zones after earthquakes.