| This study is based on two key issues of the tectonic stress field and the seismogenic environment-stress and faulting.The main contents include the following aspects: 1).Using P-wave initial polarity data,the tectonic stress field of the whole Anhui region is calculated using a comprehensive seismic mechanism solution method,and supported by different data and methods;2).A study on the relocation of areas with high clustering of seismic events;3).Using the relocation seismic results to fit the geometry parameters of the buried fault surface and then calculate the sliding properties of the occluded fault surface based on the results of the tectonic stress field;4).Provide a kinetic interpretation of the frequency of blind faults or small earthquakes in relation to the regional background tectonic stress field,described separately as follows.First,observations from January 2008 to December 2020 in the Anhui region(29.4° to 34.6°N,114.9° to 119.6°E)were collected for a total of 6869 seismic events and 19,873 P-wave polarity data.Following a 0.2° × 0.2° gri d,the results obtained based on the composite focal mechanism solution metho d cover almost the entire Anhui region,and based on the inversed stress field results,the following perceptions are obtained.The compressional axis of the Anhui section of the Tanlu Fault Zone is dominated by near-NE and NEE dire ctions;the compressional axes in northern and south-western Anhui are spread in near-EW directions;the compressional axes in western Anhui are spread in NNW directions;the compressional axes in the whole Anhui area are generally in EW directions,and the tensional axes are distributed in NS directions.The non-uniformity and complexity of the stress field results are also consistent with the stress characteristics of the region being at the junction of several plates.Then,in order to further verify the accuracy of the integrated seismic focal mechanism solution in this chapter,the seismic focal mechanism solution given by previous authors was collected in this study and combined with the grid search method to invert the stress field results of the whole Anhui region,and the comparison found that the main compressive stress axis in the whole region is near EW direction,and the dip angle only differs by 1.27°;the extensional stress axis is near NS direction,and the dip angle differs by 8.99°,both axes are near horizontal and the middle axis is near vertical.This is a typical strike-slip stress system.This is consistent with the results of the classification based on the principle of classifying earthquake focal mechanisms based on horizontal strain rosette classification.Secondly,this study adopts a double-difference pinpointing method to pinpoint the earthquakes in the study area for the cluster seismic events in the‘Huoshan' window,a hotspot area studied by a wide range of scholars.Four velocity models(AH2015;South China model;Crust1.0;USTClitho2.0)were configured and the influence of the velocity models on the relocation results was discussed,and a comparison of the re-location results reveals that the residuals of USTClitho2.0 are relatively small and more in line with the actual conditions in the ‘Huoshan' area.Finally,the geometrical parameters(strike and dip)of three seismic f aults(BB',CC',DD')in the "Huoshan Window" area were calculated based on t he precise localization results of the cluster seismic events.The geometry of th e three faults(BB',CC',DD')in the area of the 'window'(orientation,dip angle);and then,based on the abundant small-earthquake P-wave initial motion data in the area,the stress field was inferred using a comprehensive seismic mechanism solution.Finally,the seismogenic faults were analyzed in the context of tectonic and stress field backgrounds,and the following perceptions were obtained.(1)The strike,dip and rake of the BB' fault is 245.7°,85.6°and 167.3°,respectively.The strike,dip and rake of the CC' fault is 231.4°,88.5°,and 173.2°,respectively.The strike,dip and rake of the DD' fault is 49.6°,87.5°and-174.7°,respectively.The three seismic sections are all right-lateral strike-slip,which are consistent with the sliding characteristics of the Luoerling-Tudiling fault.(2)The relative shear stress and normal stress produced by the regional stress field on the three faults show that the normal strain release of the three faults is basically under the action of the tectonic stress field,but affected by pre-existing weak zones.(3)The three seismic sections are the wild goose-type right-lateral strike-slip branch fracture of the Mozitan-Xiaotian fault,whose slip properties are caused by pull-apart interaction of the right-lateral strike-slip of the Shangcheng-Macheng Fault and South End of the Tanlu Fault. |
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