Shallow Crustal Structures and Buried Active Faults Revealed by Seismic Reflection Profiles in the Northwest of Beijing Plain

Abstract

AbstractGeological and geophysical studies suggest that there are many buried active faults and buried Quaternary basins below the Beijing plain. In order to investigate shallow crustal structures, geometry of buried faults, fault activity and the relationship between shallow and deep structures in this area, a mid‐deep seismic reflection profile with 60‐fold and several shallow seismic reflection profiles across buried faults were completed in the northwestern region of Beijing plain in 2006. The results show that the depth of crystalline basement is about 3~6 km along the profile. The seismic reflection section shows a set of strong reflected phases with good lateral continuity above the crystalline basement, which should be the sedimentary rock systems of Cenozoic, Mesozoic, and Paleozoic era. Beneath the crystalline basement, there is a series of weak reflected events with poor continuity possibly representing the crystallized rock system with comparatively strong metamorphism or other non‐layered rock systems. The faults revealed by mid‐deep and shallow seismic reflection profiles present consistent upper‐lower relationship and have been significantly active since Quaternary, which play an important role in controlling the rift valley‐horst like basin and range tectonics as well as the thicknesses of Cenozoic strata in this region. The study results can further improve the understanding of the neotectonic activity in the Beijing area, and the used exploration method and technology can serve as a reference for the survey of deep‐shallow structures in other areas.