Geomorphic Index and Activity Characteristics of the Mid-Segment of Jiali Fault
435 tributary basin standardised steepness indices(ks),43 tributary valley width-height ratio(VF),55 basin area-elevation integral index(HI),10 tributary channel longitudinal profiles and knick points were extracted by using 30 m resolution SRTM DEM data for the middle section of the Jiali Fracture Zone(Niwuxiang-Guxiang).Based on the river steepness indices of different reaches and the distribution characteristics of a series of knick points along the river longitudinal profile,the study area was divided into three are-as for comparative analysis:upstream,the south side and the north side of the lower part.The upstream ks and HI were lower than the downstream values,while the VF values were higher than the downstream values.The study results indicated that the tectonic up-lift activity in the downstream area of the middle section of the fault was strong,while the uplift in the upstream area was relatively weak.Five tributaries from the north and south were selected respectively for analysis in the downstream part of the Niwuxiang-Guxiang section,and the remote sensing interpretation results showed that the fracture spread roughly along the southern side of the river valley,and was mostly in the same position as the development of low elevation knick points of the first-order tributaries on the southern side.Combining with the results of the field fracture profile survey and dating result,the analysis suggested that the middle section of the fracture was of early Holocene or Late Pleistocene age,and was accompanied by significant recoil extrusion in addition to right-slip activity.The reason was that the middle section of the fault was located directly north of the eastern tectonic junction of the Qinghai-Xizang Plateau,and it was assumed that in addition to the eastward transport of the Qiangtang block,the recoil was the result of the continuous northward pushing of the tectonic junction.
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