Abstract: Recent studies have confirmed that the bedrock temperature changes when the crustal stress changes, and the information of dynamic change in crustal stress can be obtained through the observation of bedrock temperature. Moreover, there are abundant fluids in the shallow crust, and the deformation of the crust will inevitably lead to the migration of fluids, which will change the bedrock temperature. The temperature change of bedrock is equivalent to the secondary fluid thermal effect caused by crustal stress change and may be an another indirect sensitive index of crustal stress dynamic change. The bedrock temperature data of Xianshuihe fault zones show that the variation of groundwater flow rate after the Kangding M_S6.4 earthquake is consistent with the zoning characteristics of co-seismic volumetric strain in the strike-slip earthquake, indicating that the variation of near-field fluid migration characteristics is probably related to the variation of co-seismic static stress change. Moreover, the response form of bedrock temperature to the dynamic change of crustal stress and its secondary fluid effect is not consistent, as the former shows step-rise characteristics, while the latter shows exponential variation. The observation of bedrock temperature itself can obtain the dynamic change information of crustal stress and the information of shallow crustal fluid migration. Compared with crustal stress change, the variation range of fluid secondary heat effect caused by stress change may be significantly magnified(approximately an order of magnitude), which is more conducive to capturing signals, and thus may even obtain precursory fluid change information.
On January 19, 2020, an M_S6.4 earthquake occurred in Jiashi, which happened in the bedrock temperature observation network. In particular, the Xike’er observation station is about 1.3 kilometers away from the epicenter, providing an opportunity to analyze bedrock temperature changes before and after the earthquake. The results showed that: 1)Obvious changes in bedrock temperature were found before and during the M_S6.4 earthquake. The appearance of co-seismic response means that these changes before the earthquake are related to the earthquake and may be precursory signals. 2)In terms of time, the bedrock temperature before the Jiashi earthquake first changed abnormally on the stable background, and the change reached the peak, and then fell back. When the earthquake was impending, there was a significant acceleration of the change, and the earthquake occurred after some time. The acceleration characteristics of change impending earthquake may be related to the meta-instability process of earthquakes. 3)Spatially, changes in temperature before the earthquake occurred in or near the seismogenic fault, and no obvious abnormal information was observed at the measurement points far away from the seismogenic fault, indicating that short-term and impending precursors are more likely the “near field” information; From the perspective of depth, the change in temperature before the earthquake was observed only at the local depth range. This implies that there is obvious uncertainty in the depth in precursor observation. Upon this, the ideal situation should be to carry out multi-depth joint observation, so as not to miss important precursor information. 4)Combining with the Kangding M_S6.3 earthquake on November 22, 2014, a comparative analysis is made. Similar to the Jiashi earthquake, the temperature at measurement points located in or nearby seismogenic fault of Kangding M_S6.3 earthquake shows significant changes. This means that change in the temperature before the Jiashi M_S6.4 earthquake is not an isolated case, and is a representative of universal phenomenon that occurs before strong earthquake. In a word, the change of bedrock temperature before and after the earthquake shows that the precursor information has the characteristics of near field, structural correlation and sensitive to stress change.

Key words: bedrock temperature, Jiashi earthquake, Kangding earthquake, seismic precursor, earthquake meta-instability

摘要： 2020年1月19日发生的伽师M_S6.4地震正好位于基岩温度观测区内, 且西克尔观测台距离微观震中仅约1.3km, 这为分析地震前后的地温变化提供了机会。 结果显示: 1)在伽师M_S6.4震前及同震均观测到了清晰的地温变化。 同震响应的出现, 意味着震前的这些变化与地震有关, 可能属于前兆信号。 2)时间上, 伽师地震前的基岩温度先是在稳定背景上出现异常变化, 变化达到峰值后回落, 一段时间后才发生地震。 临近地震时, 基岩温度呈现明显的加速上升变化。 这种临震前的加速特征可能与地震亚失稳或成核过程有关。 3)空间上, 震前变化出现在发震断层或附近, 而在距离发震断层较远的测点基本没有观测到明显的异常信息, 预示着短临前兆更倾向于 “近场”信息; 从深度上看, 只有局部深度的位置能观测到震前变化, 前兆观测在深度上存在较明显的不确定性, 理想的情况应该是开展多深度联合观测, 避免漏掉关键的前兆信息。 4)结合2014年11月22日康定M_S6.3地震的观测记录进行了对比分析, 结果表明: 与伽师地震类似, 康定M_S6.3地震前发震断层或附近基岩温度测点的观测结果也出现了明显变化, 这意味着伽师地震前的温度变化并不是孤例。 总之, 从地震前后的基岩温度变化看, 前兆信息具有近场、 构造相关及对应力变化敏感的特征。

关键词: 基岩温度, 伽师地震, 康定地震, 地震前兆, 地震亚失稳