GEOMORPHIC EVOLUTION AND ITS IMPLICATION FOR THE FAULT ACTIVITY IN THE DAIHAI DRAINAGE BASIN
岱海流域地貌演化及其对断裂活动性的指示意义

The Daihai drainage basin(DDB),a closed basin,is situated on the northeastern corner of the Ordos Massif.In its center there is the Daihai fault basin between the Manhanshan piedmont fault(MPF)on the north and the southern margin fault(SMF)on the south.We applied the DEM data,elevation-area integral value,and drainage branching ratio to the study of the geomorphic evolution and its influencing factor in DDB.We emploied the Rivertools(a GIS analytical software)to extract the data of the geometrical shapes and boundaries of the 11 sublevel individual watersheds in DDB,7 in the ridges north to MPF,4 in the ridges south to SMF.Afterwards,we took advantage of ArcGIS Desktop(another GIS analytical software)to calculate the elevation-area integral values and the drainage branching ratios of all the 11 watersheds.The elevation-area integral values of the 7 northern watersheds vary from 0.567 to 0.324,decreasing eastwards;while those of the 4 southern watersheds vary from 0.373 to 0.425,with no sharp difference from west to east.The drainage branching ratios of the 7 northern watersheds vary from 2.079 to 2.628,increasing eastwards,while those of the 4 southern watersheds are between 2.066 and 2.138,with no sharp difference from west to east as well.Both of the 2 indexes of the 7 northern watersheds document a decreasing tendency of the activity of MPF from west to east,while both of those of the 4 southern watersheds do not reflect any obvious difference in the activity of SMF from west to east.There exists a clear negative linear correlation between the 2 indexes of 7 northern watersheds;the principal factor synthesized from the 2 indexes varies from 1.337 to-1.699 and assumes a remarkable decreasing tendency eastwards.The results of the multiple analytical methods used all indicate that the activity of MPF decreases from west to east,while the activity of SMF shows no significant variance from west to east.