Experimental Analysis of Gulf Coast Fracture Patterns

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Abstract
Gulf Coast faults are normal faults with the exception of those around salt domes. Normal faults must accommodate both a horizontal and vertical component of displacement. The horizontal component increases the distance between two points on opposite sides of the fault surface. The vertical component is larger and must be accommodated simultaneously by the same mechanism. Experiments show that horizontal and vertical components can be derived from one motion in practically horizontal surfaces. The accumulation of all horizontal components in the Gulf Coast embayment makes considerable horizontal displacement of the sedimentary blanket necessary. The regional Gulf Coast fault pattern and its many local variations are therefore thought to be caused by regional gravity creep of the sedimentary blanket into the basin. As creep takes place the sliding sediments break away from the stationary ones forming a marginal graben, and, nearer the coast, asymmetrical down-to-basin faults with reverse drag, and antithetic faults. Creep has taken place for a long time as is proved by the fact that there was sedimentation after and during faulting in association with many growth faults. The first faults may well have been the peripheral ones as they occurred first in the experiments. Faults within the basin are later, as shown by the facts that they were buried under sediments, grew upward into them, and transect younger formations. Local domes show local fault patterns, but at many places the regional fault pattern suppressed local ones. Experimentation suggests that a general mechanism can explain both regional and local phenomena rather simply by one general cause which is modified by specific local conditions within the large and heterogeneous Gulf Coast embayment.

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