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Title:: Geochemical Characteristics and Genesis of Soil Gas CO₂ in the Longxian-Baoji Fault Zone

作者:: 刘洁¹; 李营²; 陈志²; 王新¹; 赵小茂¹; 冯希杰¹; 王景丽¹; (1.陕西省地震局,陕西西安 710068; 2.中国地震局地震预测研究所中国地震局地震预测重点实验室,北京 100036)

Author(s):: LIU Jie¹; LI Ying²; CHEN Zhi²; WANG Xin¹; ZHAO Xiaomao¹; FENG Xijie¹; WANG Jingli¹; (1.Shaanxi Earthquake Agency,Xi'an 710068,Shaanxi,China)(2.Institute of Earthquake Forecasting and Key Laboratory of Earthquake Prediction,China Earthquake Administration,Beijing 100036,China)

Keywords:: soil gas CO₂; intensity of gas activity; stable carbon isotope; fault activity

摘要:: 陇县—宝鸡断裂带位于青藏块体东北缘,属于鄂尔多斯块体西南缘弧形断裂束的最南段。为对比分析该断裂带的分段活动性强弱特征,利用断裂带逸出气CO₂的地球化学特征进行反演。布设6条跨断层土壤气CO₂测线,进行2期测量,共计获取150个土壤气CO₂组分浓度,计算了气体的相对活动强度; 收集了60件CO₂气体样品,测试了其碳同位素组成。结果表明:岐山—马召断裂的气体活动强度(1.56～2.70)比固关—虢镇断裂的气体活动强度(1.73～1.75)大,且岐山—马召断裂上的CO₂碳同位素组成比固关—虢镇断裂上的CO₂更靠近深部物质端元。位于南段的岐山—马召断裂的地下构造连通性较好,断裂闭锁程度较低,而位于北段的固关—虢镇断裂气体活动性较弱,闭锁程度较高,未来发生地震的危险性较高。

Abstract:: The Longxian-Baoji Fault Zone is located in the northeast edge of the Qinghai-Tibet Block and belongs to the southernmost segment of the arc fault belt in the southwest edge of the Ordos Block.To compare the activity of the Qishan-Mazhao Fault in the south of the Longxian-Baoji Fault Zone with the activty of the Guguan-Guozhen Fault in the north,we study the geochemical features of the soil gas CO₂ in the faults.Six survey profiles for surveying CO₂ are deployed across the two faults and two periods of observation are carried out.We obtain 150 observed values of CO₂ component concentrations.In addition,we collect 60 CO₂ samples for stable carbon isotopic composition measurements.We find that the intensity(1.56-2.70)of CO₂ activity in the Qishan-Mazhao Fault is greater than that(1.73-1.75)in the Guguan-Guozhen Fault.And the source of the CO₂ in the Qishan-Mazhao Fault is closer to the end member of the deep materials.This suggests that the connectivity of the underground structures of the Qishan-Mazhao Fault is better and the fault's locking degree is lower.Meanwhile,the gas activity in the Guguan-Guozhen Fault is weaker and the fault's locking degree is higher.Thus,the earthquake risk in this fault zone is higher.