Using River Terrace Deformation To Study Lintong-Chang'an Fault

This article takes Lintong - Chang'an as an example to study active tectonics in loess crystallizing field using fiver terrace deformation.LintongChang'an fault is in the Weihe basin,and it is the boundary fault of Lishan uplift and Xi'an hollow.It controls the deposition,the landform and the river system,so it is very typical in the loess crystallizing field.According to the predecessor studies,it indicated that this fault has intense activity in Holocene.For this study,I collect local drilling material here,measuring river terrace and analyzing the throw of latter Pleistocene stratum,and according to the result of above to analyze the activity of Lintong-Chang'an fault from early Pleistocene.It is thought that Lintong-Chang'an Fault had an intense acivity and it has act weakly from middle Pleistocene.Now it is mainly small dislocation or small tension crack.1.The landform performance of Lintong - Chang'an fault in quaternary periodIt is very different both sides landform of the fault zone.The southeastern side is the loess plateau area,but northwestern is Xi'an hollow area.It displays fault scarp and loess steep ridge in the fault zone region.At the same time,there is tectonic denudation depression as well.This phenomenon is obvious on Bailuyuan platform and Shaolingyuan platform,and ground fissure grows in front of the platform.At the same time,there are two long rivers between the loess platform,Changhe River and Bahe River.The river undercuts deeply,and forms multi-stage river terrace. Bahe River has 5 stage terrace in Lantian section and other places 4 stage terrace commonly.Chanhe River generally grows 4 stage terraces in Shaolingyuan platform. So we get a good condition to begin the research work.This research discovered that Lintong-Chang'an fault breaks the 4th terrace to 90m,3rd terrace only several meters, but 1st and 2nd haven't deformed.2.Investigation of the exhibition and activity of Lintong - Chang'an faultThis fault located in loess platform where the agricultural developed station is, and the frequent cultivation as well as the artificial destruction is serious.At the same time the loess corrodes easily,so the surface is hard to state originally.But in front of the loess plateau,there are many flushes,and all of them locate in the fault zone.So we can see the breaks in the ditch.In this study,we discover 57 breakpoints. According to the statistical data,it indicates that the S₁-S₅ paleosoil breaks 1m-2m mostly.According to the results of the two aspect work,this paper has discussed the activity of Lintong -Chang'an fault after early Pleistocene.At last,it is thought that Lintong-Chang'an Fault had an intense activity before middle Pleistocene and it has acted weakly from middle Pleistocene.Now it displays mainly small dislocation or small tension crack.Through the analysis result of the Lintong- Chang'an fault,it is a useful method to study the active structure in the loess crystallizing field using the terrace distortion method,especially in the station which the fault cuts the river.It has a very high scientific nature,and it is thought the consummation and the promotion of this method connected in the related research has practical value.