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ABSTRACT

Scaled analogues and seismic reflection profiles are used to illustrate the influence of (sub-salt horizon) basement faults on triggering diapirism. Model diapirs formed above or close to the basement faults and penetrated their faulted overburden. In the models, basement faults initiated subsidence of a half graben, where more overburden material accumulated, and also enhanced differential loading above an existing salt, which then flowed updip to the low pressure zones in the uplifted block. Deformation in the overburden covered a wider zone of faulting than the discrete basement fault which caused the deformation.

Natural examples from the Danish Basin, Dutch Central Graben, Gulf of Mexico, and North Sea show that those diapirs which are associated with basement faults are rooted to or lie close to them. However, model results show that diapirs triggered by basement faults are not necessarily located directly above the faults. Differential compaction enhances differential loading resulting in thicker sediments on the downthrown sides of basement faults where mobile salt is forced to flow to the uplifted areas.

Model results suggest that basement faults may weaken overburden units by faulting, produce differential loading and differential compaction, and therefore encourage diapirism.

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