The Geochemical Characteristics On Fault Gas Of Main Active Faults In The Danger Earthquake Area Of Gannan And Longnan

The area of southeast in Gansu is located at the eastern edge of Qinghai-Tibet block andlocated in the middle of North-South Seismic Belt, whose boundaries and internaldevelopment group of active fault, and which is one of the intense tectonic activity regions inthe northeastern Tibetan Plateau. In this paper, we put the dangerous region of main activefaults as the research object in the area of southeast in Gansu, and surveyed in the researcharea of the main active fault zone by multiple measuring line, then researched the relationshipbetween Geochemical characteristics of mercury and radon in fault soil gas and active fault.And we were in analysis of spatial features in intensity of mercury and radon in fault gas, thespatial and temporal characteristics of seismicity of the z-value, b-value. Then we discussedcorresponding relationship in space by comparing spatial features between the intensity ofmercury and radon in fault gas and z-value, b-value. In addition, we speculated the trend ofconcentration of mercury and radon in fault gas in use of good corresponding relationshipbetween the intensity of mercury and radon in fault gas and b-value and the temporalevolution of relationship in recent10years in the area of southeast in Gansu，which isbeneficial to layout chemical detection line in fault with optimization，and will be moreeffective to track and monitor the seismic hazardous area，and then provide the basis of deepunderground fluid activity for seismic hazard analysis and dangerous areas judgment. Initiallyformed as follows:(1)Fault gas geochemistry abnormal morphology has a good reflect on faultcharacteristics. The abnormal peak group number and range size of mercury or radon in faultgas has an indication on fault nature. Fault gas abnormal morphology is asymmetric, the lineconnection for the abnormal peak is strike of abnormal interface; turning steeply is locationsurface projection of fault point; slow side interface is propensity.(2)The spatial distribution characteristics of fault gas concentration are obvious; bothmercury and radon concentration in fault gas are synchronous on the spatial distribution in thearea of southeast in Gansu, but the radon is more obvious. At the same time, mercury andradon concentration distribution in fault gas is different with different active fault zone inspace.(3)Mercury and radon concentration distribution in fault gas is relevant to seismicactivity parameters of z-value and b-value; and mercury and radon concentration distribution in fault gas have a better correspondence with b-value than z-value. The correspondentrelationship of concentration distribution in fault gas, b-value and z-value is that highconcentration is corresponding to high b-value, negative z-value; otherwise, lowconcentration is corresponding to low b-value, positive z-value.In addition, the b-value segmentation feature by time evolution in the past10years ismore apparent in area of southeast in Gansu. The three region of b-value segmentation featurereflected seismic activity of active fault belt in the area of southeast in Gansu, and alsoreflects the regional stress changes to a certain extent. Both concentration distribution in faultgas and b-value have segmentation feature, which has a corresponding relationship.According to the high concentration of fault gas intensity corresponding to a high b value, andthe combination of the southeast area of Gansu this10years of b-value spatial evolutioncharacteristics, which will be more effective to track and monitor the seismic hazardous area，and then provide the basis of deep underground fluid activity for seismic hazard analysis anddangerous areas judgment.