Regional contemporaneous faults occur on the inshore sides of major Gulf Coast depocenters and develop as normal faults with major negative displacements on the Gulf, or depocenter, side. Displacement appears to be continuous, first increasing and then decreasing in rate, during the period of rapid sediment accumulation for a particular depocenter. As new depocenters are established higher in the section and gulfward, regional contemporaneous fault zones are established on the inshore sides of the new depocenters. The distribution and characteristics of the faults suggest that they are sediment-related and are caused by large differences in compaction of adjacent sediment masses.

A model was constructed to test the hypothesis that differential compaction could cause faulting in unconsolidated sediment. Mud volcanoes were produced during uniform, passive compaction, and faults were produced during forced, differential compaction of clay-water suspensions. Stress analysis indicates that the faults are simple shear failures. The stress field is approximately that of a point-supported beam with distributed loads along part of the length.

Differential compaction faults may occur wherever large changes in total compaction of adjacent sediment masses occur, either as a result of change in thickness or of facies change. In the Gulf Coast area they occur on the inshore side of flexures, where both thickening and change from sand to clay facies occur in the offshore direction.