Saribudak, et al., reported in mid-2018 that ongoing sediment deposition and related deformation in the Gulf of Mexico cause faulting in coastal areas. These faults are aseismic and underlie much of the Gulf Coast area including the city of Houston in Harris County, Texas. Considering that the average movement of these faults is approximately 8 cm per decade in Harris County, there is a great potential for structural damage to highways, utility infrastructure, and buildings that cross these features. Using integrated geophysical data, we have investigated the Hockley Fault, located in the northwest part of Harris County across Highway 290.
The authors' magnetic, gravity, conductivity, and resistivity data displayed a fault anomaly whose location is consistent with the southern portion of the Hockley Fault mapped by previous researchers at precisely the same location. Gravity data indicate a significant fault signature that is coincident with the magnetic and conductivity data, with relatively positive gravity values observed in the down-thrown section. Farther north across Highway 290, the resistivity data and the presence of fault scarps indicate that the Hockley Fault appears to be offset to the east, which has not been previously documented. The publicly available LiDAR data and historical aerial photographs of the study area support the authors' geophysical findings. This important geohazard result impacts the mitigation plan for the Hockley Fault because it crosses and deforms Highway 290 in the study area. The nonunique model of the gravity and magnetic data indicates strong correlation of a lateral change in density and magnetic properties across the Hockley Fault. The gravity data differ from the expected signature. The high gravity observed on the down-thrown side of the fault is probably caused by the compaction of unconsolidated sediments on the down-thrown side. There is a narrow zone of relative negative magnetic anomalies adjacent to the fault on the down-thrown side. The source of this magnetization could be due to the alteration of sediment mineralogy by the introduction of fluids into the fault zone.
The authors concluded that magnetic, conductivity, and gravity data successfully imaged a fault signature across the structure in the southern portion of the study area. Two-dimensional resistivity data provided useful information for identifying the lithologies from the surface to 40 m depth. In addition, the resistivity data acquired on the south and north of Highway 290 suggest an easterly shift on the trace of the Hockley Fault. This interpretation is supported by publicly available LiDAR data and the authors' observations of surface deformation across the study area. New modeling of gravity and magnetic data over the fault, using resistivity models for constraint, was performed. The nonunique model of the gravity and magnetic data shows the strong correlation of a lateral change in density and magnetic properties across the Hockley Fault.
[For a comprehensive coverage of Houston faulting and subsidence, and associated issues: http://www.i2mconsultants.com/downloads/corp/JGG-1-015.pdf ]
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