GEOCHEMICAL CHARACTERISTICS AND GENESIS OF SOIL GAS IN THE PINGYUAN M5.5 EARTHQUAKE
At 2:33 am on August 6,2023,a M5.5 earthquake occurred in Pingyuan county,Dezhou city,Shandong Province.The faults within the epicenter and adjacent areas are deeply buried by the thick Quaternary sediment cover on which human activity is intensive,which makes it difficult to determine the location of the buried active faults from the surface based on geological and geomorphological evidences.It is necessary to detect the location of the buried active faults around earthquake areas and estimate their seismic risk.In this study,based on the epicenter distribution direction of major earthquake and aftershocks,seismic and geological data of earthquake areas,and damage degree of local buildings,4 survey lines with a length of 30km were arranged across the epicenters and adjacent areas,and the concentrations of Rn,CO2 and Hg in soil gas were measured on site,and the results are as follows:(1)There are obvious spatial differences in the concentrations of soil gas near the epicenter and its vicinities within the distance of 30km.Gas concentrations are relatively high near the epicenter areas and the east and west ends of 4 arranged survey lines,in contrast to those which are relatively low in other non-structural control regions.The spatial distribution pattern of Rn concentration in soil gas is basically consistent with that of CO2,which may be due to CO2 used as a carrier gas of Rn to migrate to the surface.At the southern end of the Lingxian-Guanxian Fault(F1),the spatial concentration patterns of Rn and CO2 gases exhibit multiple peaks or wide anomalous zones.It is speculated that the deformation zone of the fault rupture at this location is relatively wide,and there may be secondary permeable fracture zones in the west of the F1.The escape form of Rn and CO2 gas indicates that there may indeed be multiple small fault branches near the F1,and the fault structure is relatively complex.(2)The spatial concentration distributions of Hg,Rn and CO2 in the epicenter areas are similar to that in its eastern region.However,in the western region of the epicenter areas,the spatial concentration distributions of Hg,Rn and CO2 vary greatly,and the Rn and CO2 concentrations near the Jiucheng Fault(F3)in the west of the epicenter regions are higher than those near epicenters.It is speculated that this phenomenon may be related to the high-concentration gas migration caused by strong seismic tectonic activities and the special nasal geological structure controlled by F3.(3)The concentrations of Rn,CO2 and Hg in the soil show high-value anomaly zones near the F1 and F3,and the concentrations of Rn and CO2 in the west of F3 exceed those in the epicenter area.After further earthquake relocation analysis,the spatial distribution of aftershocks exhibit a trend from F1 to F3.Combined with geochemical and geophysical research results,it is inferred that Pingyuan M5.5 earthquake should be related to the deep tectonic activities of F1 and F3.Above research results show that the soil gas geochemical method can be applied to define the location and distribution direction of the buried faults with thick overburden,which provides an important criterion for earthquake trend tracking analysis.This study is of greatly scientific significance in determining the dynamic source and genetic mechanism of Pingyuan M5.5 earthquake,identifying potential strong earthquake hazard areas,and assessing the risk of future earthquakes in the study area.
Pingyuan M5.5 earthquakeFault soil gas concentrationLingxian-Guanxian FaultJiucheng FaultTectono-geochemistry
万方数据
维普
