Late Quaternary Activity Of The Shuiyu Fault In The Datong Basin

This paper regards the Shuiyu fault in the northwestern margin of Datong basin as the study area,with using historical aerial photos,fault exposures to define geometric characteristics of the Shuiyu fault.Using trenching and the sequence of gully knickpoints to establish the paleoseismic event sequence of Shuiyu fault.Based on the comprehensive methods such as trenching,gully geomorphology and chronology,as much as possible to obtain the complete characteristics of the activity of Shuiyu fault in the late Quaternary.The seismic hazard in the future can be assessed by using the quantitative parameters of the activity of the Shuiyu fault.This research can provide essential data for earthquake disaster prevention in the Datong area.The research results show that based on the historical aerial and satellite image pairs to extract relative original Digital Orthophoto Map(DOM)and Digital Elevation Model(DEM),and the early topographic maps to extract the control points of aerial photographs,By extracting DEM and DOM with a resolution of 2 m from the stereo pairs of historical aerospace and satellite films in Datong area,which can obtain the original topography and geomorphology near the "invisible" section of Shuiyu fault.Based on the comprehensive analysis of the paleo-seismic events revealed by the geological sections and the trenches,we obtain five paleo-seismic events from the Shuiyu fault since 26,000 years ago,which were 9930±900 cal BP,14190±320 cal BP,14610±380 cal BP,18250±3160 cal BP,and 23550±2520 cal BP,respectively.In this study,we use differential GPS to measure 43 longitudinal gully profiles across Shuiyu fault in the southeastern margin of Cailiang Mountain,and get no less than seven knickpoint sequences.According to the catchment area,we get five paleo-seismic events of Shuiyu fault since 26,000 BP through the knickpoint sequence.The knickpoint sequences were classified according to the watershed area and the five paleo-seismic events of Shuiyu fault were obtained from the knickpoint sequences since 26,000 years ago.It is consistent with the occurrence time of paleoseismic events by geological sections and the trenches,which indicates that this paper is feasible to study the paleoseismic sequence of Shuiyu fault through the Sequence of gully knickpoints.Finally,mutual comparison and analysis show that a relatively complete sequence of palaeo-earthquake supported by geomorphic and sedimentary evidence has been established in the past 26,000 years,indicating that five palaeo-earthquake events have occurred in Shuiyu fault since 26,000 years ago.The latest one has a vertical displacement of 1.3-1.6 m and a corresponding palaeo-earthquake of Mw?6.7.The seismic risk of Shuiyu fault zone in Datong Basin cannot be ignored,especially the southern section of Shuiyu fault is located in Yudong,a new urban area in Datong City.Residential areas,where factories and schools are densely distributed,so the risk of earthquake disaster is high,and the earthquake in the future is likely to cause great casualties and property losses.Therefore,it is necessary to pay much attention to Shuiyu fault,and the necessary monitoring should be strengthened,and earthquake disaster prediction and early warning should be done well.At the same time,to be built in Yudong of Datong and large engineering facilities projects should be distributed outside the Shuiyu fault zone,and strengthen their seismic capacity.