2021年青海玛多M_(W)7.4地震地表破裂带CO_(2)脱气特征

CO_(2) Degassing characteristics in the co-seismic surface rupture zone of the 2021 M_(W)7.4 Maduo earthquake,Qinghai,China

大气圈温室气体CO_(2)浓度的增加是人为排放和自然过程排放共同作用的结果,其中活动断裂带、火山地热区等地质源温室气体释放是导致大气温室气体浓度增加的重要自然因素。活动断裂带是地球脱气的重要通道之一,释放规模巨大的CO_(2)温室气体,尤其是在地震时气体释放会有明显的增强。2021年5月22日玛多M_(W)7.4地震在地表产生了约160km长的破裂带。利用静态暗箱法在破裂带开展了系统的CO_(2)通量测量,获得了震后破裂带CO_(2)脱气特征。结果表明:1)玛多M_(W)7.4地震地表破裂带平均CO_(2)释放通量为22.25g/(m^(2)·d),最高CO_(2)释放通量为103.18g/(m^(2)·d)。CO_(2)通量剖面具有对称的特点,在剖面中心点主破裂处通量值最高,远离主破裂面,通量值逐渐递减;2)沿地震地表破裂带走向CO_(2)释放通量和同震水平位移具有较好的对应关系,同震水平位移大的破裂位置,具有较高的CO_(2)释放通量;3)玛多M_(W)7.4地震地表破裂带震后年CO_(2)释放量为0.76 Mt,释放规模相当于中国大陆新生代典型火山-地热区的3.5%。活动断裂带尤其是地震后产生的地表破裂带,其CO_(2)释放量对大气圈温室气体的贡献不可忽视,需要引起重视和深入研究。

The increase of greenhouse gas CO_(2) concentration in the atmosphere is the result of the combined action of human emissions and natural process emissions.Among them,the emission of greenhouse gases from geological sources such as active fault zones and volcanic geothermal areas is an important natural factor leading to the increase of greenhouse gas concentration in the atmosphere.The active fault zone is one of the important channels for the degassing of the earth,which releases huge CO_(2) greenhouse gases,especially during earthquakes.Due to the continuous collision between the Eurasian plate and the Indian plate,a large number of active fault zones are developed on the Tibetan Plateau.It is necessary to strengthen the research on CO_(2) emissions from the active fault zones of the Tibetan Plateau,which will provide a necessary basis for the estimation of the total geological source of atmospheric CO_(2) in China's Mainland.The Bayan Har block is located in the northern part of the Tibetan Plateau and is one of the most seismically active areas in China.The Maduo M_(W)7.4 earthquake on May 22,2021 occurred near the northern boundary of the Bayan Har block and produced a rupture zone of about 160km long on the surface.We laid out 12 CO_(2) flux profiles along the surface rupture zone.Each profile is about 500~600m long and contains about 22 flux measuring points.We used the static chamber technique to measure the CO_(2) flux and obtained the CO_(2) degassing characteristics of the rupture zone after the earthquake.The results indicated(1)The average value of CO_(2) emission flux from a single profile of the surface rupture zone of the Maduo M_(W)7.4 earthquake is between 12.19g/(m^(2)·d)and 40.05g/(m^(2)·d)and the maximum value is between 31.07g/(m^(2)·d)and 103.18g/(m^(2)·d).The average CO_(2) emission flux of all 12 profiles is 22.25g/(m^(2)·d),and the maximum CO_(2) emission flux is 103.18g/(m^(2)·d).The maximum flux value of CO_(2) flux profile is higher in the western and eastern segments,followed by the western central segments,and the lowest in the eastern central segments.The CO_(2) flux profile is symmetrical,with the highest flux value at the main rupture zone,and the flux value decreases gradually away from the main rupture zone.(2)There is a good correspondence between the CO_(2) release flux along the strike of the surface rupture zone and the co-seismic horizontal displacement.The rupture location with large co-seismic horizontal displacement has a high CO_(2) release flux.(3)The annual amount of CO_(2) released into the atmosphere by the Maduo M_(W)7.4 earthquake surface rupture zone is 0.76 Mt after the earthquake,which is equivalent to 3.5%of the typical Cenozoic volcanic geothermal area in China's Mainland.The contribution of CO_(2) emission from active fault zones,especially the surface rupture zones generated after earthquakes,to the greenhouse gases in the atmosphere cannot be ignored,which requires attention and in-depth research.