SEISMOLOGY AND GEOLOGY ›› 2023, Vol. 45 ›› Issue (3): 735-752.DOI: 10.3969/j.issn.0253-4967.2023.03.008

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PRELIMINARY STUDY ON CHARACTERISTICS OF SOIL GAS Rn AND CO2 DEGASSING IN THE MAIN FAULT ZONES OF XIONG'AN NEW AREA

WANG Jiang1,2)(), CHEN Zhi3),*(), ZHANG Fan2), ZHANG Zhi-xiang2), ZHANG Su-xin1,2)   

  1. 1) Hebei Hongshan Giant Thick Sedimentation and Earthquake Hazards National Field Scientific Observation and Research Station, Shijiazhuang 050021, China
    2) Hebei Earthquake Agency, Shijiazhuang 050021, China
    3) Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China
  • Received:2022-11-30 Revised:2023-02-16 Online:2023-06-20 Published:2023-07-18

雄安新区主要断裂带土壤气体的Rn与CO2脱气特征

王江1,2)(), 陈志3),*(), 张帆2), 张志相2), 张素欣1,2)   

  1. 1) 河北红山巨厚沉积与地震灾害国家野外科学观测研究站, 石家庄 050021
    2) 河北省地震局, 石家庄 050021
    3) 中国地震局地震预测研究所, 北京 100036
  • 通讯作者: * 陈志, 男, 1983年生, 研究员, 主要研究方向为活动构造带流体地球化学特征及其成因机理, E-mail: dugu_830822@163.com
  • 作者简介:

    王江, 男, 1984年生, 2010年于桂林理工大学获矿物学、 岩石学、 矿床学专业硕士学位, 高级工程师, 主要从事地震地下流体、 构造地球化学监测与研究, E-mail:

  • 基金资助:
    河北省省级科技计划项目(20545401D); 国家重点研发计划项目(2019YFC1509203)

Abstract:

Based on the analysis and processing of field mobile observation data, soil gas Rn and CO2 degassing characteristics in the main fault zones of Xiong'an New Area(XNA)and its effects on the regional environment was preliminarily studied. Repeated observations of soil gas concentrations and fluxes in 2020 and 2021 for the seven measurement lines on the buried faults show that strong degassing characteristics exist in the main fault zones of XNA.
The range of variation of the mean soil gas Rn fluxes for each profile is from 71.44 to 335.35mBq/m2·s, and the range of variation of the mean CO2 fluxes is from 25.96 to 78.23g/m2·d; the range of variation of the mean Rn concentration intensity is from 0.91 to 2.30, and the range of variation of the mean CO2 concentration intensity is from 1.13 to 2.61, which are comparable to the degassing intensity of soil gas in other typical fault and earthquake zones in the world. Except for the flux of Rn in the Niudong branch fault 1 and CO2 in the Niudong branch fault 2, the average values of Rn and CO2 fluxes in 2021 are higher than those in 2020.The maximum variation of soil gas Rn flux is 116%in the Niudong Fault, and the maximum variation of CO2 flux is 370%in the Niudong Fault; the variation of soil gas Rn concentration intensity is 119%in the Niudong Fault, but there is no significant variation of concentration intensity in other faults in both periods.
The observation and analysis found that the areas of high soil gas concentration anomalies on the three seismic profiles in XNA are highly coincident with the distribution of deep faults, showing a concentrated degassing phenomenon along the fault zones. The AA' seismic profile on the west side exposes three hidden fractures, which are the Taihangshan Fault, Rongcheng Fault, and one unnamed fault on the west side. The AA' soil gas Rn and CO2 concentration profiles, corresponding to the location of the upward trend line of the Rongcheng Fault and the unnamed fault on the west side, show the characteristics of simultaneous single-peak type high-value anomalies of Rn and CO2 concentrations. This phenomenon may indicate that the Rongcheng Fault and the unnamed fault on the west side are still highly active.
The BB' soil gas profile shows two areas of high soil gas concentrations respectively in the east and west. The western high value area shows synchronous peak anomalies of Rn and CO2 concentrations, and the location of the anomalies is basically consistent with the upward extension direction of the Xushui-Dacheng Fault. In the east, only single-peak anomalies in CO2 concentration are observed, and the magnitude of the anomalies is more significant than that in the western section, but there is no corresponding fault. Therefore, the synchronous peak anomalies of Rn and CO2 concentrations in the western section should be related to the fault activity of Xushui-Dacheng Fault, while the single-peak anomalies of CO2 concentrations in the eastern section may be non-tectonic.
The CC' seismic profile contains the Taihangshan Fault, Niudong Fault, Niudong branch fault 1, Niudong branch fault 2, and several secondary faults. The peak anomalies of soil gas Rn concentration in the soil gas profile are detected at different degrees and near the locations corresponding to the upward extension trend lines of Niudong Fault, Niudong branch fault 1, and Niudong branch fault 2. All three peak anomalies of soil gas Rn concentration may be related to the activities of Niudong Fault, Niudong branch fault 1, and Niudong branch fault 2. However, the single-peak CO2 concentration anomaly is detected only above the Bazhou Depression, and the anomalous area basically overlaps with the area where the Bazhou Depression is located. The Bazhou Depression is one of the main areas of concentrated population in XNA, and the biological activity is relatively strong. According to the results of the existing study that soil gas CO2 generated by biological activities may also be the main recharge source of CO2 gas released from fault zones in the basin, the large-scale CO2 concentration anomalies detected above the Bazhou Depression may also be generated by biological activities in the basin.
The results show that strong degassing characteristics exist in the main fault zones of XNA. The environmental effects of gas release from the main fault zones in XNA are evaluated by combining with the comprehensive prevention and control standards for indoor gas environmental pollution. The highest value of radon gas release in the main fault zone of XNA reaches 675mBq/m2·s in the Rongcheng Fault, and 395.70mBq/m2·s and 334.84mBq/m2·s in the Nudong branch faults respectively, the results indicate that it is necessary to carry out comprehensive radon prevention treatment for the buildings above the Rongcheng fault and Nudong fault zone. The preliminary estimation results of CO2 release show that the daily contribution of CO2 degassing from the main fault zones of XNA to the atmosphere is about 1 622.56t, and the annual contribution is as high as 0.59×106t. Attention should be given to its impact on the regional environment.
The research results in this paper are significant for urban planning, environmental management and comprehensive assessment of the environmental impact of gas release from the fault zone in XNA.

Key words: Xiong'an New Area, soil gas flux, Rn, CO2, concentration, Rongcheng Fault, Nudong Fault

摘要:

文中基于对野外流动观测数据的分析处理, 初步研究了雄安新区主要断裂带土壤气体的Rn与CO2脱气特征及其对区域环境的影响。经观测分析发现, 新区3条地震剖面上方的土壤气体浓度高值异常区域与深部断裂的分布高度吻合, 展现出沿断裂带集中脱气的现象。受局部生物活动影响, 个别断裂区段土壤气体Rn和CO2可能存在不同的补给来源, 导致个别区段的Rn和CO2浓度高值异常区域不一致, 以及Rn和CO2浓度与通量测值之间较弱的相关性。计算结果显示, 新区主要断裂带存在强脱气特征, 各剖面土壤气体Rn通量平均值的变化范围为71.44~335.35mBq/m2·s, CO2通量平均值的变化范围为25.96~78.23g/m2·d; Rn浓度强度平均值的变化范围为0.91~2.30, CO2浓度强度平均值的变化范围为1.13~2.61, 与国内外其他典型断裂带及地震带的土壤气体脱气强度相当。结合室内气体环境污染综合防治标准对雄安新区主要断裂带释放气体的环境效应进行评估, 结果表明, 新区容城断裂的氡气释放最高值达675mBq/m2·s, 牛东断裂2条分支的最高值分别达395.70mBq/m2·s和334.84mBq/m2·s, 有必要对建在容城断裂和牛东断裂带上方的建筑物进行综合防氡处理。CO2释放量的初步估算结果表明, 新区主要断裂带的CO2脱气对大气的日贡献量约为1 622.56t, 年贡献量高达0.59×106t, 其对区域环境的影响应予以重视。文中的研究成果对于新区城市规划、 环境治理及断裂带释放气体环境影响的综合评估具有重要的科学意义。

关键词: 雄安新区, 土壤气体通量, Rn, CO2, 浓度, 容城断裂, 牛东断裂