Lineations and Faults in the Texas Coastal Zone

Over 7,000 miles of lineations have been observed on aerial photographic mosaics of the Texas Coastal Zone. These lineations, in part, represent the surface traces of faults originating in the Tertiary sediments and propagating through the Quaternary sediments. The extrapolation of subsurface faults from specific oil and gas reservoirs are commonly coincident to lineations in those areas. Some extrapolated fault traces weave back and forth across lineations for 10 to 20 miles and then coincide with another lineation and follow it for 20 miles. They also may partially represent fracture-joint systems within the sedimentary deposits of the Gulf basin. In the Houston-Galveston area of land subsidence, lineations commonly correspond with zones of active faulting. Coincidence of lineations and active faults occurs along the Hockley escarpment and in the complexly faulted Ellington Air Force Base-NASA area. Many lineations coincide with zones of differential subsidence; fifty percent of intersections of subsidence profiles and lineations occur at points of differential subsidence. Differential subsidence may be a precursor to active faulting; the land surface flexes before fault displacement is evident. With increased regional subsidence, active surface faults may be expected to develop within zones of differential subsidence. Movement on faults in the Houston area is being activated and accelerated by ground-water withdrawal. The rate of fault movement on the Long Point fault and Eureka Heights fault increases and decreases as the piezometric surface rises and declines, respectively. Land subsidence and fault activation can be expected in areas of the Texas Coastal Zone other than the Houston-Galveston area if in these areas there is extensive ground-water withdrawal from shallow (less than 3,000 ft) fresh-water artesian aquifers. In these areas surface faulting and/or differential subsidence would be expected to occur in part within the zones defined by the lineations.