基于密集台阵的四川长宁页岩气开发区地震b值特征分析  

Characteristics of seismic b-value of Changning shale gas region,Sichuan,from a dense seismic array

作　　者：黄柳 赵爱华[1] 吴庆举[1] 徐政语 潘佳铁[1] 张风雪[1] 姚志祥[1] Huang Liu;Zhao Aihua;Wu Qingju;Xu Zhengyu;Pan Jiatie;Zhang Fengxue;Yao Zhixiang(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;PetroChina Hangzhou Research Institute of Geology,Hangzhou 310023,China)

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]中国石油杭州地质研究院,杭州310023

出　　处：《地震学报》2024年第5期825-843,共19页Acta Seismologica Sinica

基　　金：科技部国家重点研发计划项目(2020YFA0710600);国家自然科学基金项目(41974065);中国地震局地球物理研究所基本科研业务费专项(DQJB21Z04,DQJB19B40)共同资助.

摘　　要：随着川南页岩气快速规模化地开采,四川长宁地区地震频发,不仅发生了大量微地震而且伴随发生了多个中强地震,地震风险持续增高。本文基于长宁地区的107个密集台站在2021年4月28日至2022年6月30日期间所记录的连续波形使用深度学习震相拾取方法所构建的观测区高分辨率地震目录,通过最大似然法计算了四川长宁页岩气开发区频度−震级关系式中的b值,对b值的时空分布特征进行了分析。结果表明:长宁地区的平均b值为1.06,长宁—双河采卤区的b值为1.25,而长宁—昭通页岩气开采区的b值为1.01,这意味着页岩气开采区可能具有更高的应力水平;b值在空间分布上呈显著的非均匀性,这种非均匀性在一定程度上反映了地下介质的不均匀性;有感地震更倾向于在低b值区域发生,且地震发生前可能会出现b值下降的情况。Changning,an area in the southwestern Sichuan basin,is characterized by abundant resources of salt mine and shale gas.With rapid and large-scale exploitation of the shale gas,this area has suffered from several moderate-to-strong earthquakes and numerous microearthquakes.The active seismicity means the potential seismic risk in the area.For the assessment of seismic risk,the seismic parameter of b in the frequency-magnitude relationship plays an important role because it can reflect the change in underground stress.To obtain the b-value characteristics in Changning area,we first constructed a high-resolution earthquake catalog with a deep learning-based method including phase picking,event association and earthquake location.The data for constructing the catalog are continuous waveforms recorded by 107 dense stations in Changning from April 28,2021 to June 30,2022.Finally,we have located more than 240000 seismic events and employed a maximum likelihood method to calculate b-values of Changning area.For the whole Changning area,b-value is 1.06 on average,larger than that of Sichuan Province(0.8).The parameter b behaves differently in the northern Changning-Shuanghe brine mining area and in the southern Changning-Zhaotong shale gas production area.Their b-values are 1.25 and 1.01,respectively,indicating that earthquakes in the two areas have distinctly different seismogenic environments.Changning area is divided into elements with a size of 0.02°×0.02°.As for each element,if earthquakes within it are not less than 50,we calculate its b-value.The resulting b-value spatial map shows significant heterogeneity,which reflects the heterogeneity of the underground media to some degree.Most earthquakes with magnitude above 4.0 occur within or on the edges of low b-value regions,so we can conclude that felt earthquakes will tend to occur in such regions.The temporal evolution of b-value from the earthquake clustersⅠ,ⅡandⅢin the southern shale-gas region of Changning area shows that the b-value is low or significant

关 键 词：四川长宁地区 B值 地震活动性 诱发地震 

分 类 号：P315.7[天文地球—地震学]