Geometry styles and quantification of inversion structures in the Jiyang depression, Bohai Bay Basin, eastern China

Abstract

Inversion structures of Jiyang depression evolved during Mesozoic and Cenozoic are classified into positive and negative inversion geometry styles. The geometry styles of the reactivated faults in the study area are attributed to their multi-phase history, which includes at least four phases of compressive deformation and subsequent subsidence caused by extensional reactivation of faults since Mesozoic. In the case of negative inversion style, the negative inversion ratios cannot be calculated by the same method of calculating the degree of positive inversion, thus a new method of quantifying the negative inversion ratio is presented. In this paper, negative inversion ratio is defined as the ratio of extensional displacement to contractional displacement measured along the fault. This method provides a useful complement to conventional estimation of the degree of inversion, and adapts to any negative inversion faults. Based on this method, we obtained the negative inversion ratios of some faults in the Jiyang depression, which indicates a decrease in deformational degree from east to west in the whole region.