A new method to evaluate the effects of mechanical heterogeneity on fault architecture in sedimentary sequences

Abstract

Geologists have long realized the important control of mechanical stratigraphy on fault nucleation, fault linkage and fault compartmentalization. However, uncertainties still exist concerning the mechanical heterogeneity of the stratigraphy because of difficulties in quantifying the mechanical stratigraphy. In this study, the average strength $S_{ave}$ of a section is calculated considering the strength and thickness of each individual layer. The strength difference $S_{\Delta }$ and normalized mechanical contrast $S_{\Delta }/S_{ave}$ are defined for each individual layer in a section. A diagram of the normalized mechanical contrast $S_{\Delta }/S_{ave}$ versus the normalized height $H/\sum _{i=1}^n{h}_i$ can then be employed to effectively evaluate the vertical mechanical heterogeneity of the stratigraphy in a section. High-frequency fluctuations between negative and positive $S_{\Delta }/S_{ave}$ values represent high mechanical heterogeneity, and vice versa. The scaled mechanical heterogeneity ${MH}_{scaled}$ can be used as an index to quantify the mechanical heterogeneity of the stratigraphy in sections with different scales. However, it is also important to realize that fault throw may promote or restrict the control of mechanical heterogeneity on faulting deformation. The mechanical heterogeneity may present limited control on the fault architecture, particularly when the fault throw is several times larger than the scale of the section. Increasing deformation rate may also minimise the control of the mechanical heterogeneity on the fault architecture.