--> --> Restoring Seismic Images Based on Structural Forward Models to Reveal the Interplay Between Faulting, Erosion, and Fluvial Processes at a Basin-Bounding Growth Fault in the Bohai Bay, China

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Restoring Seismic Images Based on Structural Forward Models to Reveal the Interplay Between Faulting, Erosion, and Fluvial Processes at a Basin-Bounding Growth Fault in the Bohai Bay, China

Abstract

Accurately applying structural forward models to seismic data hinges on the extent to which the kinematic assumptions of each method approximates the kinematics of the seismically-observed structure. Generally, the suitability of any given model is judged by its ability to reproduce the seismically imaged geometry of a structure. However, structural deformation is just one geologic process that can influence observed seismic stratigraphic geometries. Syn-deformational growth strata deposited during deformation respond to both fault-related kinematics as well as sedimentary processes. This leads to geometrically complex seismic stratigraphic patterns in growth strata that not fully matched by a kinematic model. We propose that as long as the structural model matches the general fault and fold geometry, the modeled fold horizons can be used to restore the bulk deformation associated with the controlling fault. This removes the geometry associated with fault-bend-folding from the seismic image but retains the general seismic stratigraphic geometry associated with depositional or non-fault related processes. We demonstrate how combining modeling and restorations reveals the interplay between fault-related folding, erosion, and fluvial processes on a regional seismic line from the Bohai Bay rift in China. The section features two linked, listric growth faults. The footwall of the main fault has been completely eroded and the hangingwall features angular unconformities and complex stratigraphic geometries. The main fault model is constrained by a clearly imaged fault plane and hangingwall folding. The model reconstructs the eroded footwall and indicates that rapid extension was accompanied by up to 7 km of footwall erosion. The seismic stratigraphy of the hangingwall growth sequence that records this period of erosion is characterized by short-wavelength undulations that are unassociated with faults. The model reproduces the broad-scale fold geometry associated with the underlying listric fault, but not the shorter wavelength undulations within the growth section. To determine if the undulations are stratigraphic bedforms, the model horizons are used to restore the growth sequence to remove the influence of large-scale folding associated with the underlying fault. The restored seismic image reveals a channel-levee system that migrates through time but is largely localized above the steeply-dipping upper extent of the fault.