Geochemistry Of Soil Gas From The Active Fault Zones In The Northern Part Of Shanxi Seismic Zone

The northernpart of Shanxi seismic zoneis joined withthe Zhangjiako- Bohai seismic zone(ZBZ)to the north.Thetectonic activity is serious in the region, and therisk of large earthquake is severe.The measurements of soil gases in the active fault zone play animportant roleforassessing the risk of active faults.The previous geochemical survey of soil gas were mainly conducted in the middle and southeastern parts of the ZBZ. The study region, however, is lack of geochemical survey of soil gas.The thesis aims at revealing the geochemical characteristics inthe northern partof Shanxi seismic zone and discussing tectonic significance of gasgeochemistry. The results have important signif icance for monitoring earthquake continuously by the gasgeochemical method and distinquishing the seismic precursor of gases in the study region.Concentrations of CO2, Rn, Hg, H2, and Hg in soil gases, flux of CO2,Rn, Hg near the suface and fluxof CO2, Rn at 1m deep in the ground were measured in 12 places(a total of one hundred and twenty sites for measuring gas concentrations, thirty-six sites for measuring flux of CO2, Rn and Hg near the suface, and twelve sites for flux of soil gas CO2, Rn at 1m deepth)across seven faults(South margin fault in yuxian-guanling basin, Northern Liulengshan Piedmont Fault, The Kouquan fault, The datong vacalno Xubao-gelaozhuang fault, The north margin fault in Tianzhen-yanggao basin, The north margin fault in Huaian basin) in May to June 2014. Concentration of Rn was measured in the field with a RTM2200 Radon Detectors.Concentrations of CO2, H2 and Hewere analyzed with an Agilent 3000 Gas Chromatography. Concentrations of Hg were analyzed with a RA-915+ Zeeman Effect atomic absorption spectrometer. Flux of Rn, CO2 and Hg were measured with the RAD7 Radon Detector, GXH-3010 E portable infrared analyzer and RA-915+ Zeeman Effect atomic absorption spectrometer in a continuous cycle suction measurement, respectively.The concentrations of Rn, CO2 in soil gas varied obviously from place to place in the study region, but concentrations of H2, He and Hg showed small spatial variation. Themean values of CO2, Rn, Hg, H2 and He concentrations have the ranges of 0.22~0.79%, 6.64 ~ 10.72 k Bq/m3, 8 ~18 ng/m3 and 1.02 ~ 1.98 ×10-6, 4.89 ~5.76×10-6, respectively. The geochemical profils of concentrations of CO2, Rn, Hg, H2, He in soil gas were characterized by monomodal or bimodal distributions.Flux of CO2, Rn, Hg near the suface and the flux of CO2, Rn at 1m deep spatial distribution aried obvious ly from place to place in the study region. The mean values of flux of CO2, Rn, Hg near the suface have the ranges of: 1.57~69.33g/m2 d, 17.33~85.07 m Bq/m2 s and 1.07~31.04 ng /m2 h. The flux of CO2, Rn at 1m deep have the ranges of:0.01 ~59.33 g /m2 d,6.24~373.87 m Bq/m2s1. Rn and CO2 in soil gas were degassed intensively in the study region. The degassing value of CO2,Hg has the ranges of: 24.05~288.68 t/dand 0.13~4.44 g/d, respectively. The mean value of flux of CO2, Rn had positive correlation relationship with mean value of CO2, Rn concentration. The value of flux of CO2, Rn increased with the depth.The spatial varation characteristic of soil gases in the different measurementplace of the same fault were mainly related to the fault activity of the measurement area.Thespatial varation characteristic of soil gases in the different measurement placeof different faults were related tothe fault activity、soil types and rock types of the measurement area.The different compents in soil gas can reflect the fault activity in the study region.