Interpretation Criteria for Seismic Recognition of Growth-Fault Systems

Olufemi Oladapo Babalola

The identification of growth faults on seismic sections requires an understanding of the basic differences between the geometry of structures and features peculiar to seismic sections compared to their actual appearance on geologic sections. On seismic sections, normal faults commonly display a curvature at depth deceptively similar to that characteristic of growth faults, thus presenting a pitfall of which the interpreter should be wary. Growth faults may be recognized on seismic sections by identifying the signatures or typical reflection patterns expected from certain characteristic features.

Stratal curvature is a growth-fault feature that is easily recognizable on seismic sections. It commonly occurs just basinward of, and above, the fault plane, and may be well developed as a rollover anticline. Bedding planes paralleling the growth-fault plane may be easily identified as a continuation of the fault plane, at depth, into the bedding-plane. Convergence at depth of the fault planes associated with a growth-fault system is another diagnostic feature observable on seismic sections.

Stratal thickening just basinward of the fault plant is also diagnostic of growth faults, as are antithetic faults that occur basinward of the fault plane, which may also suspend a "graben" or sediment block that has more prominently curved strata. The fan geometry of stratal surfaces converging at a fulcrum seaward of the fault plane also is a good criteria for recognizing growth faults.

Another growth-fault feature requiring interpretive skill to recognize on seismic section is the shale ridge or "turtle-back." This feature can be identified from the haphazard or random reflectors on the shoreward side of the fault plane. Seismic reflector characteristics diagnostic of growth faults include curved and disjointed reflectors adjoined laterally by stratified and continuous reflectors, and the decrease toward the surface, in both number and curvature, of the numerous curved reflectors present at depth.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.