Hundreds of residential, commercial, and industrial structures in the Houston metropolitan area have sustained moderate to severe damage owing to their locations on or near active faults. Paved roads have been offset by faults at hundreds of locations, butted pipelines have been distorted by fault movements, and fault-induced gradient changes in drainage lines have raised concern among flood control engineers. Over 150 faults, many of them moving at rates of 0.5 to 2 cm/yr, have been mapped in the Houston area; the number of faults probably far exceeds this figure.
This report includes a map of eight faults, in north-central and western Houston, at a scale useful for land-use planning. Seven of the faults, are known, to be active and have caused considerable damage to structures built on or near them. If the eighth fault is active, it may be of concern to new developments on the west side of Houston. A ninth feature shown on the map is regarded only as a possible fault, as an origin by faulting has not been firmly established.
Seismic and drill-hold data for some 40 faults, studied in detail by various investigators have verified connections between scarps at the land surface and growth faults in the shallow subsurface. Some scarps, then, are known to be the surface manifestations of faults that have geologically long histories of movement. The degree to which natural geologic processes contribute to current fault movement, however, is unclear, for some of man’s activities may play a role in faulting as well.
Evidence that current rates of fault movement far exceed average prehistoric rates and that most offset of the land surface in the Houston area has occurred only within the last 50 years indirectly suggest that fluid withdrawal may be accelerating or reinitiating movement on pre-existing faults. This conclusion, however, is based only on a coincidence in time between increased fault activity and increased rates of withdrawal of water, oil, and gas from subsurface sediments; no cause-and-effect relationship has been demonstrated. An alternative hypothesis is that natural fault movements are characterized by short—term episodicity and that Houston is experiencing the effects of a brief period of accelerated natural fault movement. Available data from monitored faults are insufficient to weigh the relative importance of natural vs. induced fault movements.
This report has a dual purpose—to provide maps of faults in parts of north-central and western Houston at a scale useful to land-use planners and to provide a limited discussion of “the Houston fault problem” (Van Siclen, 1967) for the interested reader. The use of scientific terminology has been held to a minimum, but where such use is unavoidable the appropriate term is followed by an asterisk (*) and is defined in the glossary.
Many readers of a companion report on faults* in the southeastern Houston area (Verbeek and Clanton, 1978) expressed a wish for amplification of the section on geologic significance of faults. This was particularly true among those in land-use planning, construction, engineering, and allied disciplines, who have periodic need of geologic information but who cannot routinely consult all of the geologic literature for relevant papers. Accordingly, this report provides a short summary of the geology of faults and a brief overview of the possible causes of current fault movement.
Active faults near Houston were first recognized over fifty years ago, when Pratt and Johnson (1926) reported sudden displacements of the land surface within the Goose Creek oil field near Baytown. By 1973, after much discussion of the subject in the geologic literature (for example, Gray, 1958; Weaver and Sheets, 1962; McClelland Engineers, 1966; Van Siclen, 1967; Sheets, 1971; Reid, 1973) some 52 faults had been recognized in the Houston metropolitan area. Aggregate length of known faults was then reported at 220 km (Reid, l973). More recent studies (Clanton and Amsbury, 1975; St. Clair and others, 1975; Verbeek and Clanton, 1978; this report plus additional unpublished data) have increased those numbers to well over 150 faults having an aggregate length of more than 500 km.
Hundreds of residential, commercial, and industrial structures in the Houston metropolitan area have sustained moderate to severe damage because of their location on or near active faults. The total number of active faults in this region is not known, but some idea of the scope of the problem can be gained from this report and a previously published map (Verbeek and Clanton, 1978) of faults in southeastern Houston (fig. 1). Together the two maps cover about 750 km2, or about 20 percent of the Houston metropolitan area, yet even, within this restricted area 100 faults with a combined length of over 230 km have been recognized. More than half of the faults mapped show clear evidence of movement during historic times. The actual percentage of active faults is probably much greater, because the opportunity to assess recent movement (based on damage to manmade structures) is lacking for large tracts of undeveloped land. Additional areas in and near Houston have comparable fault densities (for example, Jacinto City and areas to the north, as well as Baytown and much of southern Houston; see fig. 2), but other areas, such as downtown Houston, appear to be relatively unaffected.
The total socioeconomic impact of faulting is large (Sheets, 1971), yet public awareness of this natural hazard has grown slowly. Fault-related problems grow worse as the region rapidly develops into neighboring highly faulted areas. Even where the presence of a fault has been a matter of public record for years, as it has for the Long Point, Piney Point, and, Eureka Heights faults (McClelland Engineers, 1966), new construction commonly takes place near or directly on the fault trace*.