2016年10月20日射阳MS4.4地震前地下流体典型异常特征及其前兆机理分析

分析2016年10月20日射阳M_S4.4地震前地下流体典型异常特征并对其机理进行讨论。该地震前的地下流体前兆异常（1）从时间进程看可分为中期趋势背景异常和短期异常；（2）从空间演化上看，在中期趋势背景阶段，异常分布在离震中300 km范围内，其在起始时间上表现为从震中向外围迁移继而向震中靠拢的特点。相较于中期趋势背景阶段异常；短期异常在空间上向震中收缩，分布在离震中100~200 km范围内，其在起始时间上，表现为向震中靠拢的特点。井水温异常变化可能是区域应力加载作用的产物，而离子浓度的变化可能是水岩反应加剧引起的。

Underground Fluid Anomalies and Precursor Mechanisms of Sheyang MS4.4 Earthquake of Oct. 20, 2016

In this paper, we summarize the characteristics of the typical underground fluid anomalies associated with the Sheyang M_S4.4 earthquake that occurred on Oct. 20, 2016, and discuss the precursor mechanisms. Our analysis results show that the underground fluid anomalies prior to the earthquake can be divided into medium-and short-term anomalies. The medium-term anomalies are distributed within a 300-km radius of the epicenter and initially migrated from the epicenter to the outer area and then near to the epicenter. Compared to the medium-term anomalies, the short-term anomalies are located much closer to the epicenter, being distributed within 100-200 km of the epicenter and migrate close to the epicenter. The spatial properties and distribution characteristics of the anomalies show that the change in the water-temperature anomalies, which occurred prior to the Sheyang earthquake, may be caused by regional stress variations.