2017—2019年松原地区4次中强地震前绥化台地电阻率异常分析

2017—2019年松原地区连续发生4次5级左右地震,在此期间距松原地区约220km的绥化地电阻率观测资料记录到了一定的异常变化。为分析震前异常与地震的关系,首先以三层水平层状模型计算了测区介质的影响系数分布,发现绥化地电阻率“夏高冬低”的反年变形态与测区的Q型电性结构有关;之后采用断层虚位错模式,以2018年松原M_S5.7地震的震源机制为例,计算了松原地区介质的变形特征,发现绥化台位于震前挤压变形增强区域,绥化地电阻率2个测道出现的下降回返变化与应力累积释放的变化形式一致;最后根据GPS数据推测,绥化台以西的地电阻率数据无显著异常,可能与东北地区的主压应变率自东向西逐渐减小有关。

Resistivity Anomaly Analysis before 4 Moderate-strong Earthquakes in Songyuan Area from 2017 to 2019

From 2017 to 2019,four moderate strong earthquakes occurred in the Songyuan area which is the most concerned earthquake hazard region in Northeast China. During that period,the apparent resistivity observation from Suihua station,about 220km away from Songyuan area,recorded some abnormal changes. To analyze the relationship between the anomalies and these moderate earthquakes,the sensitivity coefficient of medium in the survey area is calculated by using the three-layer horizontal layered model. It is found that the anti-annual variation of the apparent resistivity is related to the Q-type electrical structure of the survey area. Then,taking the focal mechanism of the 2018 Songyuan M_S5.7 earthquake as an example,we used the fault virtual dislocation model to calculate the deformation characteristics of the medium in Songyuan area. We found that Suihua station was located in the area of compressive deformation enhancement before the earthquake,and the decrease and return changes of the N15°E and N75°W observations are consistent with the change form of stress accumulation release. Finally,based on GPS data,there is no significant anomaly found in the apparent resistivity at west of Suihua station,which may be due to the decrease of the main compressive strain rate from east to west in northeast China.