Numerical simulation analysis of seismically triggered load and ball-and-pillow structures in the lacustrine sediment

[Objective] Seismically triggered soft-sediment deformation structures (SSDSs) in the lacustrine sediments serve as reliable stratigraphic records for studying paleoearthquake events in tectonically active regions. Load and ball-and-pillow structures, as one of the common types of SSDSs, are often attributed to reverse density gradients between different sedimentary layers driven by gravity. However, the formation processes and mechanisms of these structures, as well as their quantitative relationship with seismic intensity remain unclear. [Methods] This study employs a FLUENT software to simulate the formation processes of load and ball-and-pillow structures in saturated sand-clay sedimentary layers with varying physical properties (density, dynamic viscosity and thicknesses) under different seismic accelerations (0.125g, 0.25g, 0.5g, and 0.8g). [Results] The results indicate that as the seismic accelerations increases, load and flame structures appear earlier and gradually evolve from small-scale load structures to larger-scale ones and ball-and-pillow structure. Under the same seismic acceleration, a larger density and dynamic viscosity difference, and a larger thickness in sand layer would result in more intense and large-scale load and ball-and-pillow structures. [Conclusions] The simulation results are generally consistent with the morphological characteristics of load and ball-and-pillow structures identified in the field investigation in the Tashkorgan area. [Significance] This finding verifies the seismic trigger of SSDSs in this region and provides a new technological insight into the study of SSDSs and paleoearthquakes.