Non-tectonic Surface Deformation

Non-tectonic phenomena that can result in surface deformation at a facility site include 

1) Glacially-induced faulting,

2) Growth faulting,

3) Collapse due to underground voids such as found in Karst terrain, and

4) Subsidence due to extensive fluid withdrawal.

 

Glacially-induced faults

Glacially-induced faults generally do not represent a significant displacement hazard because the conditions that created them are no longer present. If residual stresses from Pleistocene glaciations are still present, these features should be investigated with respect to their relationship to current in-situ stresses.

Growth faults

Large, naturally occurring growth faults, as found in the coastal plain of Texas and Louisiana, can pose a surface displacement hazard even though offset most likely occurs at a slower rate than that of tectonic faults, they shall be identified and avoided in siting, and their displacements shall also be monitored. Some growth faults and antithetic faults related to growth faults are not easily identified; therefore, investigations of the potential amount and character of displacement shall be undertaken in regions where growth faults are known to be present.

Underground cavities

The existence of cavities in some geological materials (e.g. limestone, gypsum, anhydrite, etc.,) may lead to ground collapse. If collapse features are present, they shall be considered and investigated with respect to their potential for causing deformation of the facility site and, if so, whether engineered stabilization measures are feasible.