Assessment On The Structural Stability Of Xi’an Region And Its Adjacent Area

Human large engineering construction and urban planning cannot leave the analysis andassessment of the site’s regional structural stability conditions,which has become the keyelements whether these can be put into effect. As a historical and cultural city, especially thefutural international metropolis, Xi’an is in the Weihe basin tectonic belt, which the faultactivities are strong, the earthquake activities are activity and the ground fissure disasters areserious. Therefore the assessment of regional structural stability has important theoretical andpractical meaning to the planning and construction of the international metropolis,and theprediction and counter measures of the earthquake and ground fissure’s.According to the principles and methods of quantitative assessment of regional structuralstability, on the basis of the analysis of influencing the structural stability of Xi’an andadjacent areas,with the influence elements as the assessment index, quantify the indexeswhich influence the structural stability.The stability assessment unit is devided and calculatedwith1km×1km grid, combined with the study area’s geological tectonic and the assessmentindex characteristics. And the calculation results are further devided into four stability grades:stability、relative stability、relative-unstability and unstability. This paper has the followingmain results:1) The main factors which influence the regional structure stability are fracture activities（including the time and rate of fracture activities）、earthquake activities、modern crust liftingmovement characteristics、ground stress field、terrestrial heat flow field、surface geologicaldisasters、lithologic features、isostatic anomaly characteristics and small earthquake activitiescharacteristics,etc.. These factors can be use as the main index to assess the structuralstability;2) Quantified and semi-quantified the structural stability assessment index, such asfracture (fracture scale、fracture activities era and rate)、earthquake（the biggest earthquakemagnitude at potential source area、basic intensity）、crustal deformation’s rate gradient、terrestrial heat flow field’s temperature、ground stress field（environmental shear stress、max-floor shear stress）、isostatic anomaly characteristics and micro-earthquake activitiescharacteristics、lithologic features and surface ground subsidence、geological disasters’ easyoccurrence degree,etc. get the assessment results of the assessment units.3)According to the normalized stability assessment index, rang out and devided the regional structural stability’s degree into4grades: unstability（IV grade: with a storng disasterenvironment period, large）; relative-unstability(III grade: with a disaster environmentperiod, sub-large); relative stability (II grade: basic security, but with a potential environmentperiod in some degree, middle）; stability（I grade: without a obviously dangerous disasterenvironment period, or less dangerous）.4) For the first time, the isostatic anomaly be quantitafied as a influence index in thestability assessment system, And the index has been quantified by using its derivative value inthe stability assessment system;5) According to the regional structural assessment results.Draw and compliation the mapof regional structural stability division.