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川东南长宁地区地震活动及b值演化特征
解孟雨, 孟令媛
中国地震台网中心, 北京 100045
摘要:
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。
关键词:  川东南地区  最大曲率法  兴文5.7级地震  珙县5.3级地震  长宁6.0级地震
DOI:
分类号:P315
基金项目: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
Seismicity and Evolution Characteristics of b-values of Changning Area in Southeastern Region of Sichuan Basin
Xie Mengyu, Meng Lingyuan
China Earthquake Networks Center, Beijing 100045, China
Abstract:
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 MS5 events,Xingwen MS5.7,Gongxian MS5.3,and Changning MS6.0,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.
Key words:  Southeastern region of Sichuan Basin  Maximum curvature(MAXC)technique  Xingwen MS5.7 earthquake  Gongxian MS5.3 earthquake  Changning MS6.0 earthquake