Identification of trigger(s) and understanding of formation mechanism(s) and process(es) are the primary focus of event sedimentology studies. The triggering of soft-sediment deformation is usually attributed to earthquake shaking, despite the lack of solid evidence to support seismic-forced deformation mechanisms and sedimentary processes, e.g., previous study cases from the Dengta outcrop, Linshan Island, Qingdao, and East China. However, soft-sediment deformation can be triggered by either earthquakes, storms, non-earthquake events involving liquefaction, gravitational loading, or slumping. In addition, the deformation can be controlled by either the Rayleigh-Taylor instability or the Kelvin-Helmholtz instability. Therefore, features of the deformation structure alone cannot be used as indicators for trigger identification. A new approach for trigger identification that involves analyzing the combined features of two event layers has been successfully applied in the Dead Sea Basin (Dead Sea Fault) in the Middle East. In this study, we apply this novel approach to analyze the deformation mechanism and trigger of a large-scale soft-deformed layer in the Dengta outcrop, Lingshan Island, Qingdao. We observe that \mathrm{①} large-scale soft-sediment deformation is in situ formed and preserved; \mathrm{②} a turbidite layer overlies the in situ deformed layer; and \mathrm{③} no background sediments have accumulated between the two event layers. These features indicate that in situ and ex situ sedimentary responses occurred simultaneously. Strong regional seismic shaking is the most plausible trigger for the contemporaneous occurrence of in situ and ex situ sedimentary responses when considering regional geological settings.