Ascertain The Late Quaternary Activity Of Kaifeng Fault (Kaifeng Segment) With Rows Of Boreholes

In the process of earthquake construction,earthquake disaster is the main threat.The current seismic fortification measures are still difficult to prevent the direct damage of artificial ground facilities caused by large earthquakes,and a more effective method is to avoid hidden active faults at the beginning of engineering construction.Therefore,in order to achieve the purpose of avoiding hidden faults,accurate positioning of hidden active faults has become an important research topic.At present,the most effective methods for detecting concealed active faults include shallow seismic exploration,joint borehole exploration,trench excavation and sedimentary age determination of stratigraphic samples.The Kaifeng fault is an important part of the Zhengzhou-Kaifeng fault zone and an important controlling fault in the middle and lower reaches of the Yellow River.According to the shallow seismic exploration data,the overall trend of the Kaifeng fault is nearly east-west to the northeast,and it tends to the north,which is a normal fault.The fault is divided into east and west branches,and the activity has obvious segmentation characteristics.The activity of the east branch is stronger than that of the west branch.Based on the geological background of weak activity in the study area,under the premise of meeting the industry standards,we set up verification holes to improve the accuracy of obtaining stratigraphic parameters,and obtain the accurate parameters of stratigraphic dislocation by tracing the marker layer and stratigraphic boundary.Through the joint drilling detection,the buried depth of the upper breakpoint of the east branch of Kaifeng fault can be identified as 20-25 m,and the buried depth of the upper breakpoint of the west branch fault is about 75 m.According to the test results of age samples,the latest activity age of the east branch of Kaifeng fault is late Pleistocene,and the latest activity age of the west branch is middle Pleistocene.The research results have proved the important role of the combined drilling method in the study of buried fault activity,and provided a new understanding for the detection of buried faults in weak active areas.