Growth Faulting and Subsidence in the Houston, Texas Area: Guide to the Origins, Relationships, Hazards, Potential Impacts and Methods of Investigation: An Update

The Houston area, and the Gulf Coast in general, is laced by numerous growth faults which are geological hazards that are known to impact and damage house slabs, building-support structures, highways and associated foundations. Water-supply wells and pipelines, oil and gas wells and pipelines, and other anthropogenic structures are also affected by growth faults, and have cost millions of dollars to repair over the years as a result of the small, but significant, movement of these faults. At depth, these faults have created economically important oil and gas reservoirs, sulfur and uranium deposits, and geopressured-geothermal energy. But they also provide pathways for dissolved uranium and radionuclides (e.g. 226radium and 222radon) and natural gas to migrate from great depths upward into Houston’s groundwater supplies in various areas within the Evangeline and overlying Chicot Aquifers. Such pathways also allow other hazardous substances from human activities to migrate vertically or from one water-bearing unit to another. Such faults impact the Houston environs as a subsurface geological hazard although their full significance has gone unrecognized for decades since the U.S. Geological Survey (U.S.G.S.) budgets for mapping the faults in the Houston area were eliminated in the late 1970s. Houston’s building foundation repair industry has since flourished in faultprone areas unsuitable for construction without foundation design accommodations. This would require a more complete knowledge of fault locations throughout the Houston area. We have reviewed and synthesized a wealth of information on the origins and characteristics of growth faults, their apparent relationship to salt domes and subsidence, and the nature of the damage and the economic impact that has occurred over at least the past four decades. With the advent of new technologies, we can now identify, map, and assess the potential for faults to cause structural damage or serve as pathways for the migration of hazardous substances. We also present a discussion of the methods in use to identify near-surface growth faults with special emphasis on Ground-Penetrating Radar (GPR) to characterize faults below roadways in the relatively high-moisture soils of the Houston, Texas area and environs. New aerial technology, such as Light Detection and Ranging (LiDAR), will help to identify the locations of many fault systems, both new and those previously known, but additional surface mapping is also required. We have called for a new hazard alert system to be developed by the U.S.G.S. that is consistent and compatible with the County Flood Plain maps to warn builders and home buyers of the potential risks known in the Houston area regarding the presence of faults. Such a system could identify faults that exist under existing pipelines and other structures, and faults where natural hazardous substances are known to occur in the groundwater of the aquifers providing a significant part of the Houston water supply and that of surrounding municipal utility districts.