玛多M_(S)7.4地震断层土壤气特征与地表破裂的相关性  

FAULT GAS OBSERVATION AND SURFACE RUPTURE FEATURE INTERPRETATION OF THE M_(S)7.4 MADOI EARTHQUAKE

作　　者：王博 崔凤珍[3] 刘静 周永胜[1] 徐胜[3] 邵延秀[3] WANG Bo;CUI Feng-zhen;LIU-ZENG Jing;ZHOU Yong-sheng;XU Sheng;SHAO Yan-xiu(State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;China Earthquake Networks Center,Beijing 100045,China;School of Earth System Science,Tianjin University,Tianjin 300072,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [2]中国地震台网中心,北京100045 [3]天津大学,地球系统科学学院,天津300072

出　　处：《地震地质》2023年第3期772-794,共23页Seismology and Geology

基　　金：国家自然科学基金(42030305,42104061);地震动力学国家重点实验室开放基金(LED2020B03);中国地震局地震科技星火计划(XH19055);国家重点研发计划(2019YFC1509203)共同资助。

摘　　要：2021年5月22日2时4分,青海省果洛藏族自治州玛多县发生M_(S)7.4地震。震后一个月,在对地震地表破裂带的展布和同震位移进行详细勘察后,有针对性地沿地表破裂带不同部位(西段、中西段、中东段、东段)布设了7条800~3000m的跨断裂测线,对土壤气Rn、H_(2)、Hg和CO_(2)进行浓度测量和气体采集,并对采集样品进行了碳同位素和氦同位素分析。测量结果表明,地表各破裂段土壤气浓度的最大值差别较大,破裂带东、西两端的气体浓度较高而中段气体浓度较低,可能与断层不同分段的破裂方式和应力分量不一致有关。土壤气中H_(2)和Hg的浓度特征具有较好的一致性,在地表破裂带内或紧邻处浓度较高。玛多M_(S)7.4地震的发震断层东端出现多条分支,破裂具有复杂性。从土壤气浓度测量结果来看,南支和北支断层的活动都较强,但北支断裂土壤气逸出浓度的曲线形态特征和断层产状不一致,可能与北支断裂地表破裂范围大且存在多条次级断裂有关。^(3)He/^(4)He测定结果表明,研究区土壤气中的稀有气体主要为大气来源,但δ^(13)C测值和CO_(2)/^(3)He计算结果显示玛多地震断层土壤气具有大气组分与地壳组分的混合特征。An M_(S)7.4 earthquake occurred in Madoi County,Guoluo Tibetan Autonomous Prefecture,Qinghai Province of China at 02:04(Beijing Time)on May 22,2021.A total of seven 800~3 000m trans-fault survey lines were targeted laid along different parts of the seismic surface rupture zone(the west,mid-west,mid-east,and the east),one month after the earthquake when the detailed field investigation of the coseismic displacement and the spread of the seismic surface rupture zone had been carried out.The soil gases were collected and the concentrations of Rn,H_(2),Hg,and CO_(2) were measured in situ.The results show that the maximum value of Rn,H_(2),Hg and CO_(2) concentrations in different fracture sections of the surface rupture was 2.10~39.17kBq/m^(3)(mean value:14.15kBq/m^(3)),0.4×10-6~720.4×10-6(mean value:24.93×10-6),4~169ng/m^(3)(mean value:30.72ng/m^(3)) and 0.73%~4.04%(mean value:0.59%),respectively.In general,the concentration of radon is low in the study area,which may be related to the thick overburden and the lithology dominated by sandstone.The concentration characteristics of hydrogen and mercury released from soil have good consistency,and the concentrations are higher at the east and west ends of the surface rupture zones but were lower in the middle of the rupture zone.This is consistent with the field investigation showing that the earthquake-induced surface rupture zone and deformation are more concentrated in the western section,while the eastern section has a large amount of seismic displacement.The fault strikes at the east and west ends of the Madoi M_(S)7.4 earthquake surface rupture have deviated from the NW direction to a certain extent,and there also exits two branching faults and rupture complexities at the east end of the main fault of the Madoi earthquake.In the west end of the surface rupture,i.e.,the south of Eling Lake,the fault strike turns to EW direction.We laid two survey lines(line 2 and line 3) at the west end of the rupture,the concentration of Rn,H_(2) and Hg escaped from line 3 is t

关 键 词：玛多M_(S)7.4地震 断层土壤气 碳同位素 氦同位素 巴颜喀拉块体 

分 类 号：P315.724[天文地球—地震学]