Holocene activities and tectonic implications of the Da’an-Dedu Fault Zone in the Songliao Basin, NE China

The Daan-Dedu Fault Zone (DDFZ) comprises multiple branches and traverses the interior of the Songliao Basin in the NE China. The studies of recent activity are significant both for tectonic deformation analysis and for strong earthquake hazard assessment of the DDFZ and the Basin interior. None of the earlier studies had found the evidence characterizing the late Quaternary activities of the DDFZ, so it is generally speculated that it is an early Quaternary fault without the ability to great events (M ≥ 7). However, geological evidence of multi-stage strong tectonic deformation of the DDFZ in the late Quaternary was discovered for the first time at the Keshan segment of the structure based on remote sensing image interpretation, surface investigation of geology and geomorphology, trench excavation, and quaternary chronology testing. Field investigation reveals that the latest activity of the DDFZ with an estimated ∼ M7 occurred at 2230 ± 30 a BP has resulted in a fault scarp with ∼ 0.6 ± 0.1 m height at the surface in a normal way, and ∼ 20 km long rupture is developed intermittently with fault scarps and sag ponds at surface. This new discovery indicates that the DDFZ experienced strong tectonic deformation during the late Quaternary, and has the tectonic background for strong earthquakes (M ≥ 7). This discovery also suggests that the Songliao Basin has been undergoing strong tectonic deformation since the Late Quaternary, which is of great significance for understanding the tectonic deformation and evolution of the Songliao Basin and entire NE China since the Late Cenozoic.