## 7 Discussion  
From 120 to 60 days before the earthquake, the bedrock showed different degrees of abnormally high temperature, which shifted dynamically, appearing closer to the epicenter  
Figure 7: The seismic activity and its LURR anomaly development and change within 100 km of the epicenter before the Jiashi earthquake. **(a)** M-T time series, where the green area is the loading earthquake enhancement time; The red vertical line indicates the loading earthquake, and the black vertical line indicates the unloading earthquake. **(b)** Computed LURR evolution sequence. The arrow indicates the time of earthquake occurrence. The spike at the end of **(a)** is the 18 January 2020 \(M_{\text{s}}\)5.4 Jiashi earthquake which is the foreshock of the Jiashi \(M_{\text{s}}\)6.4 earthquake. This earthquake is not included in the calculation of LURR and has no impact on the LURR anomaly. over time, indicating that the ground temperature changes reflected the development of the seismogenic region. [PERSON] et al. [60] found a similar anomaly in geophysical observation data before the Juzhaigou \(M_{\rm s}7.0\) earthquake in China in 2017. [PERSON] et al. [61] also found that mild earthquake activity before the earthquake accelerated toward the epicenter in a study of the nucleation process of the Changey \(M_{\rm s}6.7\) earthquake in Japan in 2011. The regional anomaly beginning far from the epicenter and approaching it may be generated by crustal stress, reflecting the action of the regional stress field, which is also indicated by the \(3.0\leqq M_{\rm s}\leqq 3.9\) apparent stress in the Keping block in the same period [62]. This indicates that the crustal stress adjustment information can be reflected through the change in ground temperature, and the crustal stress adjustment reflects the spatial-temporal process of earthquake preparation, which can be applied to detect the occurrence of earthquakes. The changes in bedrock temperature appeared at three observation points (Gedaliang, Siker, and Xiaohaizi) five days before the earthquake, and the peak fluctuation appeared synchronously. The fluctuations began approximately 15 days before the earthquake, and the amplitude was accelerated. The rock temperature both increased and fluctuated before the earthquake. This change in temperature may indicate that the rock mass is also in a state of acceleration and vibration. According to the studies presented by [PERSON] et al. (2020), there were also marked anomalies in the gravity high-gradient zone before the earthquake [63]. It is speculated that the fault had entered a stage of acceleration and vibration at this time, which is the key to sub-instability [40]. Sub-instability indicates increased stress. The LURR reflects dynamic changes in the meso-constitutive relation of the rock in the source area. When the rock system is in the elastic stage, the LURR is low (approximately 1); when the system is in the expansion stage, the LURR is greater than 1. When the peak loading/unloading response is reached, the rock system may have entered a sub-instability stage. At this time, the LURR decreases. As shown in Figure 7b, the peak LURR appeared 19 days before the earthquake, and the synchronous coupling between rock temperature and the ionosphere five days before the earthquake may indicate that the rock shifted from the steady state to the sub-instability stage (BC segment in Figure 8). The rock change rate is accelerated by the slope of the straight line L2 in Figure 8. The constitutive curve of rock shows the change of rock during stress strengthening. When the stress is low, the system is in the elastic stage, and the changes are recoverable. When the stress is high, the rock is in the dilatant process. With the development of cracks, the deformation is irrecoverable. When the stress reaches point B, it exceeds the limit of the rock, and the system enters the stage of sub-instability. In this stage, accelerated generation of cracks can be observed.