2018年安徽无为ML4.1地震地下流体前兆异常特征

对2018年4月6日无为M_L4.1地震前的地下流体前兆异常特征以及该地震的震源机制解进行了分析, 结果表明, 无为地震前的异常分布在距震中64~233 km范围内, 这些异常在时间进程上, 可分为中期趋势背景异常和短临异常, 主要以中期趋势背景异常为主。 这些中期趋势背景异常均表现为水位的破年变变化。 从空间演化上看, 2018年安徽无为M_L4.1地震前出现的中期趋势背景异常沿着长江破碎带有序分布。 这种比较明显的异常群体性特征为地震预测提供了较好的依据。 震源机制解结果显示, 节面I的走向为NE向, 节面Ⅱ的走向NW向。 反演的震源机制的P轴(主压轴)方向为NE向(70°), 倾角近水平(7°)。 无为地震震源机制解所得主压应力作用方向与无为地震前异常展布方向相同。 这说明地震孕育过程中区域应力加载作用和流体前兆响应具有密切关系。

Typical Underground Fluid Anomalies of the Wuwei,Anhui ML4.1 Earthquake Occurred in 2018

This paper analyzed the typical underground fluid anomalies and the focal mechanism of Wuwei M_L4.1 earthquake occurred on April 6^th, 2018. The results show that the anomalies appeared before the 2018 Wuwei earthquake scattered in the range of 64~233 km. According to the duration, it includes medium-term trend anomalies and short-term anomalies, and most of them are medium-term trend anomalies. These medium-term trend anomalies are abnormal the annual variation of water level. They also have certain regularity on spatial evolution. The medium-term anomalies are distributed along the fracture zone of the Yangtze River. The results of focal mechanism solution show that the direction of the nodal plane Ⅰ is NE and the nodal plane Ⅱ is NW. The P axis (principal axis) is NE70°, and the dip is 7°. The direction of the main compressive stress obtained by the focal mechanism solution of the Wuwei earthquake is as the same as the distribution of the underground fluid anomalies of the earthquake. It probably indicates that the underground fluid response is closely related to the regional stress loading in the seismogenic process.