华山山前河流地貌参数及其构造意义

摘要

Based on DEM data and ArcGIS software,we extract the geomorphic parameters of drainage basins and rivers that flow through the Huashan piedmont,which include stream length-gradient index (SL),stream-power incision model normalized channel steepness index (ksn),hypsometric integral (HI),valley floor width to valley height ratio (Vf) and mountain front sinuosity (Smf).Study shows that all parameter indexes have obviously different distributions roughly bounded by Huaxian and Huayin.In the Huaxian to Huayin section,the stream length-gradient index has extremely high abnormal values near the fault,the values of river mean SL,mean ksn,HI,Vf and Smf are concentrated in 500 ～ 700,120 ～ 140,0.5 ～ 0.6,0 ～ 0.1 and 1.0 ～ 1.1,respectively.Between Lantian and Huaxian and between Huayin and Lingbao,the parameter indexes distributional characteristics are largely the same,with the values in 300～500,100 ～ 120,0.4～ 0.5,0.2 ～ 0.6and 1.2～ 1.5,respectively.Comprehensive analysis suggests that tectonic activity is the primary factor responsible for these differences.We divide each geomorphic parameter into three classes (strong,medium,and low) and calculate the relative active tectonics(Iat) of the Huashan piedmont.The results show that the Iat values in Huaxian to Huayin section are in 1.0 ～ 1.5,those at other places are in 1.5～3.0,indicating that the tectonic activity from Huaxian to Huayin is most intense,while that of other places are relatively weak.Field geological investigations show that the Huashan piedmont fault can be divided into Lantian to Huaxian section,Huaxian to Huayin section and Huayin to Lingbao section.In Huaxian to Huayin section the fault has been active several times since Holocene indicative of strongest activity,while in Lantian to Huaxian section and Huayin to Lingbao section the fault was active only in the late Pleistocene and its activity was weaker as a whole.Tectonic activity of the Huashan piedmont derived from river geomorphic parameters is consistent with field geological investigations,indicating that geomorphic parameters of rivers can be used to characterize activity of faults on a regional scale.%基于数字高程模型(DEM)空间分析技术,系统提取了华山山前河流相关地貌参数,包括河流坡降指标SL、河流水力侵蚀模型标准化陡峭指数ksn、流域盆地面积高程积分HI、谷底宽度与谷肩高度之比Vf、山前曲折度Smf等.研究表明,各参数指标大致以华县及华阴为界,空间上差异分布,表现为华县—华阴段河段SL在断裂附近出现极高值,河流SL均值、ksn均值、HI值、Vf值以及Smf值集中在500 ～ 700、120～140、0.5～0.6、0～0.1及1.0～1.1之间;蓝田—华县段及华阴—灵宝段的指标分布特征大致相同,上述指标值集中在300 ～ 500、100～ 120、0.4～0.5、0.2～0.6及1.2～1.5之间.综合分析发现,构造活动是造成上述指标差异的主要因素,对各指标进行构造活动等级划分,计算出华山山前相对构造活动强度(Iat),结果显示在华县—华阴段Iat值集中在1～1.5之间,其他部位集中在1.5～3之间;表明华山山前华县—华阴段构造活动最强,其他部位活动相对较弱.华山山前构造活动主要受控于华山山前断裂.野外地质调查表明,华山山前断裂在华县—华阴段活动最强,全新世以来仍发生过多次活动;在蓝田—华县段及华阴—灵宝段断裂仅在晚更新世有过活动,未见全新世活动迹象,活动性整体偏弱.利用河流地貌参数获取的华山山前构造活动强弱与野外地质调查得出的结论一致,表明以河流地貌参数作为构造活动的研究对象,能有效地反映区域的差异构造运动.