Interactions between buried mass-transport complexes and subsequent slope failures on a passive margin

Mass-transport complexes (MTCs) are common features on all continental margins, with stacked MTCs indicating repeated slope failure. This suggests that MTC generation and emplacement may precondition a slope to fail again, although direct evidence for this is currently lacking. Determining the relationship between MTC development and slope stability is important, given its implications for understanding long-term basin evolution and geohazard assessment. Here, we use 3-D seismic reflection data from the Kangaroo Syncline, offshore Northwest Australia, to investigate how preexisting MTCs can prime subsequent failure events. We interpreted 11 MTCs that constitute ∼80% of the total stratigraphy of the post-Miocene interval, with individual MTCs spanning areas ≤2500 km2. We show that (1) lithological heterogeneity present within a sedimentary succession due to MTC emplacement can impact the location of subsequent slope failures; (2) topography formed by a buried MTC can enhance the erosive ability and affect the transport pathway of subsequent slope failures; (3) differential compaction between debrite matrix and blocks can produce a rugose MTC top surface that can influence the distribution and stratigraphy of subsequent slope failures; (4) the thickness pattern of buried MTCs can provide a mechanism for predicting the depocenter of future slope failures; and (5) the nature of the sedimentary succession, the aseismic setting, the presence of fluid venting systems, and slope oversteepening can collectively contribute to the preconditioning of recurrent MTCs in the Kangaroo Syncline. Our results show that buried MTCs have profound effects on the location, nature, geometry, and hazard potential of future slope failures. Therefore, investigating the interaction between stacked MTCs is a crucial component of future geohazard impact assessments.