The movement age of hidden fault and analysis on width of its effect zone from shallow seismic sounding and drilling data

摘要

Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parame-ters. In process of data processing, we obtained a high-qualitative shallow seismic reflection sounding profile byusing the techniques such as filtering, edition surgical blanking, prediction deconvolution, fitting static correlationof first arrival time, and velocity analysis. Comprehensive analysis on the information of reflection wave groupsalong the seismic sounding profile and the stratigraphic and neogeochronological data obtained from many drillsnear the sounding line reveals that the upper termination of the detected fault zone is located at depth of 75～80 m,in the Middle Pleistocene deposits dated to be about 220 ka BP. The continuity, discontinuity, increasing and de-creasing amount of reflection wave groups and change of their configurations, in combination with geologicalcolumns of drills, permitted us to know that the width of upper termination of the fault zone is 100 m. It can beinferred from the variation of number of reflection wave groups along the profile that the scarp of hidden fault is200 m wide and the fault is a synsedimentary active fault in the Early Pleistocene and the early stage of MiddlePleistocene. No tectonic movement, which offset the covering deposits, had occurred since the late stage of Middle Pleistocene.