GROWTH FAULTS (HOUSTON - GULF COAST)
FIELD TRIP STOPS – THIS STOP SHOWS THE PRESENCE OF GROWTH FAULTS IN HOUSTON, TEXAS. EMPHASIS IS GIVEN TO THE LONG POINT FAULT.
LOCATION: Cutting across large parts of West Houston from northeast to southwest, from Route 290 to Beltway 8, just north of I-10.
GEOLOGIC FEATURES: Growth Faults within the Texas Coastal Plain
DESCRIPTION: Growth Faults are Normal Faults representing the slumping of sediment towards the basin along the Continental Margin due to general subsidence. Movement along a fault is commonly episodic and when active can reach about 1.5 inches/year. Seismic energy release is not generally associated with these faults, however small earthquakes have been known to occur. These fault types are of great interest to the oil industry as they aid in the formation of anticlinal and stratigraphic traps. They are particularly abundant along the Gulf of Mexico.
In West Houston proper there are two well-known Growth Faults – (a) the Long Point Fault, and (b) the Piney Point Fault. Locations of these faults can be seen on the maps below. Of these three, the Long Point Fault is by far the most notable being responsible for much damage to buildings and roads, exhibiting some of the largest vertical displacements. In actuality, within the area around Houston, there are dozens of Growth Faults.
(1) Draw a Cross-Section through the Long Point Fault illustrating surface expression as well as movement in the subsurface.
(2) What types of damage can you expect to your home should it have been built across a Growth Fault?
(3) CHALLENGE: Explain at least two possible causes for faulting in the Houston area. (Hint: Examine the Jurassic Louann Salt and Salt Tectonics; Groundwater withdrawal due to industry; Differential sediment compaction)
-Etter, Evelyn (ed), 1981, Houston Area Environmental Geology: Surface Faulting, Ground Subsidence, Hazard Liability, Houston Geological Society, 164 pp.
-Reid, William M. 1973. Active Faults in Houston, Texas. The University of Texas at Austin, Ph.D. Disseration, 122 pp.
Figure 1 - Map of major Growth Faults in West Houston as compiled by students in my Advanced Geology class. Students were assigned different sections of the city and asked to map the fault traces on a USGS Topographic Contour Map, noting the downdropped side (side facing the tick marks).
Figure 2 - Closer view of the major two faults in the area, the Long Point and Piney Point Faults.
Figure 3 - House built across the Long Point Fault. Notice the down-dropped side of the house and nearby road to the left of the photo. (Photo by Thomas Danner; ca. 1997))
Figure 4 - A closer view of the home in Figure 3. The red line illustrates the deviation from the horizontal. (Photo by James Moore; ca. 1997)
Figure 5 - The front of this house was built across the Long Point Fault. Note the large foundation crack in the center of the photo with the down-dropped block to the left. (Photo by James Moore ; ca. 1997)
Figure 6 - The left side of house has subsided due to the Long Point Fault. Note especially the cracks in the driveway as well as the inability of the garage door to touch the ground. (Photo by E.J. Ramos III and Gaston Santos ; ca. 1992-93)
Figure 7 - The Long Point Fault crosses Gessner Rd, a major north-south thoroughfare. The asphalt is cracking and will soon break into smaller pieces at which time the road will need to be repaved at this location. (Photo by E.J. Ramos III and Gaston Santos ; ca. 1992-93)
Figure 8 - A typical change in the level of the road across a Growth Fault.
Figure 9 - A camera placed on the roadway on the Footwall of the fault zone.(Photo by Thomas Danner ca. 1997)
Figure 10 - Another typical dip in the roadway caused by a Growth Fault. (Photo by Thomas Danner; ca. 1997)
Figure 11 - One can clearly see the effects of the Long Point Fault running underneath this building. Note the left side of the building that has been down-dropped.(Photo by E.J. Ramos III and Gaston Santos ; ca. 1992-93)
Figure 12 - Here the effects of the Long Point Fault are displayed the the twisting of the doors in the door-frame as well as the cracking in the asphalt as the right side of the photo is dropped relative to the left side of the photo. (Photo by E.J. Ramos III and Gaston Santos ; ca. 1992-93)
Figure 13 - Notice both the down-dropping of the wall to the left of the photo as well as the numerous attempts to fill in the areas where stresses have separated the bricks. (Photo by E.J. Ramos III and Gaston Santos ; ca. 1992-93)
Figure 14 - As in Figure 13, tending to cracks in the brickwork is a constant chore.
Figure 15 - The escarpment of the Long Point Fault is seen here in a vacated area near Gessner Rd.