Discussion on stress drop mechanisms of seismogenic faults before earthquakes

In order to explore the regular relationship between the imminent stress change of seismogenic faults and their instability process, this paper conducts a study on the phenomenon and mechanism of the stress drop of cross-scale rock mass samples before earthquakes. Through calculation, analysis and re-interpretation of typical seismic experimental data and field stress monitoring data, the pre-earthquake stress and strain changes of different scales are studied. The results show that the experimental data from rock blocks, boreholes to crustal scales all reveal that there is a sudden decrease in the stress(stress drop) before the fault fails. The pre-earthquake stress drop phenomenon spans 3 to 6 orders of magnitude in space, and the early response time of the stress drop covers 1 to 6 orders of magnitude, indicating that the larger the scale and quality of the media involved in the earthquake, the longer the precursor response time. Field borehole stress monitoring data show that there is a linear positive correlation between the stress drop and the early response time with natural earthquakes. The inherent plastic properties of the seismogenic fault rock mass make the overall collapse of the fault later than its mechanical imbalance. In addition, the fault slip needs to overcome the irregular asperities on its surface, and the differential stress-strain loading rate of the process leads to different stress-strain reply on the time scale. This research explains may be the underlying mechanism that stress drop can precede earthquakes. © 2021, Science Press. All right reserved.