Browsing by Subject "Faults (Geology) -- Texas -- Gulf Region"

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Identification of surface faults by horizontal resistivity profiles: Texas Coastal Zone
(University of Texas at Austin. Bureau of Economic Geology, 1978) Kreitler, Charles W.; McKalips, Dawn G.
The land surface in the Texas Coastal Zone is interlaced with active and potentially active surface faults. They are subtle features which are difficult to identify until they have caused damage to manmade structures. To date (1978), significant damage has resulted. Faults intercept 2 airports, interstate highways at 11 different locations, and railroad tracks at 28 locations. Faults also pass through 11 residential communities. More than 200 houses in these communities in Harris and Galveston Counties show structural damage because of faulting. Fault movements of only a few inches per decade can cause significant structural damage, and no architectural style or structural design is immune. Foundations break, and cracks extend up the exterior and interior walls of the structure. Although breaks in buildings and highways are one of the best criteria for identifying surface faults, the damage has already occurred. Kreitler (1976) has listed four criteria that can be used to identify the presence of a surface fault before a structure is built. They are recognition of (1) topographic scarps; (2) shallow subsurface faults, using electrical logs or other geophysical data and subsequently extrapolating the fault to land surface; (3) shallow subsurface faults, by coring or trenching; and (4) the surface trace of lineations observed on a fault (lineation), using black-and-white, color, and color-infrared aerial photographs or other remote sensing techniques. This paper presents and evaluates another technique for the detection of surface faults--the use of horizontal electrical resistivity profiling. In the Texas Coastal Zone, similar surficial geology commonly occurs on both sides of a fault. Furthermore, shallow subsurface fault displacements are very small (less than 10 feet). It was anticipated that the small subsurface fault displacements might create slight lithologic or hydrologic variations on either side of the fault. Variations in electrical properties caused by lithologic or hydrologic differences, as well as fault gouge, should be marked by anomalous resistivity profiles. Consequently, resistivity profiles might provide another method for predicting and mapping faults.
Lineations and faults in the Texas coastal zone
(University of Texas at Austin. Bureau of Economic Geology, 1976) Kreitler, Charles W.
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.