Active normal faulting along the Seerteng Shan, North China: Geometry and kinematics

摘要

Although rotation of fault blocks during seismic and long-term periods has long been recognized in extensional tectonic regimes, the geometry and kinematic behaviors of normal faults at outcrop scale have scarcely been investigated in sufficient detail. In this study, combining with the analysis of high-resolution topography acquired by small unmanned aerial vehicle (sUAV) using the structure-from-motion (SfM) technique, we present the results of our field observations on the structural characteristics of the Seertengshan Piedmont Fault (SPF), a major active normal fault bounding the northern margin of the Hetao Graben, North China. Although previous studies have reported the recent tectonic activity of this fault including timing of most recent earthquake, average slip rate and repeat time of paleo-earthquakes, few of them have focused on geometric patterns of the outcropping fault zones, which provide excellent outcrop-scale examples to investigating geometry and kinematics of active normal faults. Besides the observed prominent fault scarps indicative of recent tectonic activity along the SPF, outcrop observations indicate that in some cases both planar and curved normal faults are developed, forming complex fault zones. Sequential development of normal faults may have rotated the early-formed fault blocks, resulting in shallowly dipping faults and highly tilted strata. Collectively, structural similarities probably exit among normal faults at multiple spatial scales. We suggest that the results of this study are also helpful for a better understanding of structural development and evolution in other actively extending areas.