Rupture characteristics and seismic assessment of the Qinling northern piedmont fault

Abstract

Research on fault rupture characteristics and behaviors, as well as the quantification of activity parameters is an important basis to evaluate the future seismic hazard. What is the upper limit of the magnitude of normal fault has received more attention in recent years, especially in the several Cenozoic grabens around the Ordos block where major earthquakes have occurred. Previous work on faults in these grabens mainly focused on paleoseismicity and tectonic activity. However, research on the rupture characteristics and behaviors of these faults is relatively weak and poorly constrained, especially where the main fault is located at the contact interface between bedrock and Late Quaternary sediments. The Qinling northern piedmont fault (QNF) is an important active fault located in the southern border of the Weihe graben, separating the Qinling Mountains from the Weihe basin. The middle section of Qinling northern piedmont fault has been intensively active since the Late Quaternary and may have a high seismic risk. Therefore, we carried out shallow seismic exploration and borehole survey, as well as paleoseismological analysis in this section. Based on the seismic reflection profile and boreholes, this work reveals that the QNF is consist of the main fault, the secondary faults and the fracture zone, together constituting a typical Y-shaped structure, with a width of ∼130.0–140.0 ​m. Combined with paleoearthquake, chronology, geology and geodesy data, the future seismic hazard of the fault is evaluated, and its maximum vertical offset and maximum seismic capacity given are 2.4–5.4 ​m and 7.0–7.8, respectively.