1. Department of Earthquake Science, Institute of Disaster Prevention Science and Technology, Sanhe, Hebei 065201;
2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249;
3. Research Center, CNOOC, Beijing 100027
The ductile deformation in an extension basin is often ignored by scholars. The huge error of two familiar methods used to calculate the extension amount("fault balance restoration" and "crust thickness change calculation")is due to the plastic deformation amount. This paper will build a model based on two methods that can calculate the "ductile extension amount" and the "fault-slip extension amount" respectively. The model is applied in Bohai Bay Basin. By the calculation, the ductile extension amount is 40% of the total extension amount in Bohai Bay Basin. This is the real reason why the extension amount which comes from the "fault balance restoration" is always less than that comes from the "crust thickness change calculation". The results show that the ductile deformation rate is proportional with the fault-slip rate. In the rifting phase, the fault slipping is severe while the ductile deformation is very fast.