This research focuses on investigating the genetic mechanisms and evolutionary processes of the superimposed multi-stage fault systems in Block 3 of Nanpu Sag

Bohai Bay Basin.The workflow herein adopted a variety of modern techniques such as 3-D seismic interpretation

physical simulation of structure and finite element numerical simulation

and took the theories of structural geology and geomechanics as guidance.We recognized the geometry and combination modes of faults

restored the paleostress state of different tectonic periods

analyzed the development and evolution patterns of faults under variable stress field

discussed the control of pre-existing structures on later fault formation and evolution

and established geodynamic models of the superimposed multi-stage fault systems in the study area.The results showed that

bounded by unconformity on the top of Shahejie Formation

the X-pattern normal faults could be divided into two vertically superposed fault systems with short-term inversion characteristics.The upper tone is a SN-trending composite extensional and sinistral strike-slip fault system with pure shear deformation being predominant

while the lower tone is a NW-SE-trending extensional fault system with single shear deformation being predominant.Distribution of geomechanical layers

later tectonic stress intensity

and angle between pre-existing fault strike and later principle stress direction were regarded as the three main factors controlling the development of superposed fault systems.The pre-existing faults could influence the redistribution of local stress field and the development of later faults

which either continued to expand along early faults

or created new faults.As a mechanical weak surface

the unconformity was easy to generate uncoordinated deformation or slipping

resulting in significant vertical discontinuous development of faults.Regionally

the formation and evolution of the superimposed fault system in Block 3 of Nanpu Sag was directly controlled by transition of tectonic stress field by Tan-Lu fault since the Paleogene.