Abstract

This paper describes briefly the history and possible causes of Quaternary faulting along the Texas Gulf Coast, with particular emphasis on faulting in the Houston metropolitan area from 1916 to the present. Data used include high-resolution seismic reflection profiles of shallow subsurface sediments, detailed well-log surveys of faulted areas, topographic maps based on land-elevation surveys of 1915-1916, structure contour maps of Tertiary marker horizons, aerial photographs dating to 1930, and direct measurements or estimates of rates of movement on selected faults, gathered over the past two decades. We interpret these data as follows:

(1) Many faults that are active today were recurrently active during late Pleistocene time as well. Observed increases of stratigraphic separation with depth suggest lengthy histories of fault movement, at least in part contemporaneous with Pleistocene sedimentation. That such faults are shallow extensions of Tertiary "growth faults", hundreds of which are known to cut deeper subsurface sediments, has been proved for some faults and is suspected for most.

(2) Recent growth in scarp heights of known faults can be reasonably inferred from examination of topographic maps based on 1915-1916 surveys. Of the many faults whose scarps are presently high enough that they are obvious elements of today's landscape, few are in evidence on topographic maps of sixty years ago. We suggest that the scarps had not yet formed, or were present in only subdued form, in 1915-1916. Sequential aerial photographs confirm that most faulting of the land surface in the Houston metropolitan area has taken place within only the last few decades.

(3) Strong evidence indicates that the extraction of fluids—water, oil, and natural gas—from compressible subsurface sediments has accelerated or reinitiated movement along faults that otherwise would exhibit much lower rates of displacement. Historic faulting apparently caused by oil and gas production has been documented at two localities along the Texas Gulf Coast. Ground-water withdrawal is suspected to be the most significant cause of faulting in metropolitan Houston, where compaction of aquifer sediments has caused the land surface to subside 0.3-2.5 m over an area of more than 6500 square kilometers.

(4) Local uplift of upper Pleistocene sediments over salt domes suggests that some modern faulting could be due to natural causes. Relatively few domes, however, have significantly warped the Pleistocene sediments above them, and there is no obvious correspondence between amounts of post-late Pleistocene uplift and the numbers or rates of movement of active faults associated with the domes. Faulting due to other natural causes, such as seaward creep of Cenozoic sediments, has been postulated but has not been documented for any historically active fault along the Texas Gulf Coast.