Research on structural evolution and dynamic processes in the Western Sag of Liaohe Depression is significant to not only oil and gas exploration

but also analysis of the evolution of Bohai Bay Basin and Tanlu Fault.According to seismic interpretation

analysis of the relationship between fault system

deposition thickness and the characteristics of fault intensity

it was concluded that the Western Sag of Liaohe Depression underwent two-phase deformation superimposition in the Paleogene.The early Eocene extensional phase including an initial fault depression stage (Es

4

) and a strong fault depression stage (Es

3

) resulted in the NE-SW-trending major normal faults and half-graben filled by the fourth and the third member of Shahejie Formation.The later Oligocene strike-slip phase during Dongying Formation caused the right-lateral strike-slip of the pre-existed basement faults and the formation of new normal fault arrays in NEE-SWW orientation.A structure style with transtension subsidence in the south part and transpression erosion in the north part formed during this stages owing to strike-slip displacement.The transition from extensional deformation to strike-slip deformation occurred during Es

1-2

.Regional field analyses and sand box simulation results show that the Eocene extensional fault system was controlled by back-arc extension stress

which was triggered by subduction roll-back of the oceanic Pacific Plate from the Asian Continent.And the Oligocene strike-slip fault system was controlled by dextral displacement of Tanlu Fault

caused by the collision of Indian-Australian Plate with the Eurasian Plate.