利用全国统一目录和流动台站目录，研究了四川盆地东南部长宁地区的地震活动特征和b值的空间分布特征。研究结果显示，长宁地区的地震活动在时间上呈现明显的分段特征，地震活动在2015年后明显增强；在空间上，长宁地区的地震活动主要集中在以28.3°N为界限的南、北2个地区，对于这2个区域的b值演化，计算结果显示出不同的分段特征。此外，研究了不同震中距下，长宁地区2018年兴文5.7级、2019年珙县5.3级和2019年长宁6.0级3次主要地震事件震前与震后的b值演化，结果表明统计范围会显著影响b值的变化特征，当计算范围为20km时，3次主震震前短期内均出现了低于背景b值90%的低b值异常，这表明在地震目录相对完备的情况下，利用低b值异常分析区域地震危险性，应采用较小范围的地震数据。

In this article,we use both unified national catalog and catalog from mobile station to study the characteristics of seismicity and the evolution characteristics of b-values in the Changning area of southeastern region of Sichuan Basin. The results show that the seismicity in the Changning area has shown obvious multi-stage segmentation characteristics in time,and the seismicity increases significantly after 2015. Moreover,earthquakes are mainly concentrated in Gongxian,Xingwen,and Junlian. For the temporal evolution of b-value of the two areas,the segmentation characteristics are different. We also study the evolution of b-value before and after the major three M_S5 events,Xingwen M_S5.7,Gongxian M_S5.3,and Changning M_S6.0,in the Changning area with different epicenter distances. The results show that the epicenter distance significantly affects the evolution of b-value. When the epicenter distance is 10km,remarkble low b-value anomalies appear in short term before all M5 earthquakes,which implies that when analyzing the low b-value anomalies or the seismic hazard,earthquake catalog within a smaller range should be used.

P315

国家自然基金项目“页岩气水力压裂与地震活动性研究”（41974068）资助