Investigation of surface faulting, Brazoria County, Texas using aerial photography, field data, well log data, seismic profiles and fault modeling.

Brazoria County is located along the nortwestern Gulf of Mexico coastal plain. Just to the north of Brazoria County, in Harris County, nearly 300 active surface faults have been identified to date. In contrast, only 25 active surface faults were known to exist in Brazoria County prior to this study even though it covers a larger area, and is located in the same geologic province, as Harris County. A rigorous investigation of surface faulting in Brazoria County was undertaken to: increase knowledge of surface faulting in the Gulf coastal region; serve as a land-use planning guide for future development in Brazoria County, and more specifically to: locate and map surface faults throughout Brazoria County; determine the distribution of faulting and how it compares to that documented in Harris County; determine if surface faulting in Brazoria County is related to known structural trends; examine the subsurface geometry and movement history of selected faults; and, test two models, the Gibb's construction and a compaction, to predict listric fault shape. This study was conducted using aerial photograph reconnaissance, exhaustive field investigations, interpretation of well log and seismic data, and application of predictive models. In the course of the investigation 105 lineaments that may represent previously unknown active surface faults were identified. The pattern of surface fault occurrence in Brazoria County is found to be very similar to that in Harris County. Surface fault patterns are determined to be related to regional growth fault trends and local salt dome density. Surface faults in Brazoria County are confirmed to be the surface expression of much larger faults present in the subsurface. In the Arcola Oil Field, interrelated movement histories of major faults and the development of related structures are traced back to the Early Oligocene. Of the tested predictive models, the Gibb's construction fails to describe listric fault shape while the compaction model is found to be an excellent predictive tool.