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The Balcones Fault Zone is a tensional structural system in Texas (USA) that runs approximately from the southwest part of the state near Del Rio, Texas to the north central region near Waco, Texas along Interstate 35. The Balcones Fault zone is made up of many smaller features including: normal faults, grabens, and horsts.1 One of the most obvious features is the Mount Bonnell Fault.2
The location of the fault zone may be related to the Ouachita Mountains, formed 300 million years ago during a continental collision. Although long-since eroded away in Texas, the roots of these ancient mountains still exist, buried beneath thousands of feet of sediment. These buried Ouachita Mountains may still be an area of weakness that becomes a preferred site for faulting when stress exists in the Earth's crust. The Balcones Fault zone was most recently active about 15 million years ago during the Miocene epoch. This activity was related to subsidence of the Texas Coastal Plain, most likely from the large amount of sediment deposited on it by Texas rivers. The Balcones Fault zone is not active today, and is in one of the lowest risk zones for earthquakes in the United States.3
The surface expression of the fault is the Balcones Escarpment, which forms the eastern boundary of the Texas Hill Country and the western boundary of the Texas Coastal Plain and consists of cliffs and cliff-like structures.
Many cities are located along this fault zone, and that is not a coincidence. Frequently, springs such as San Pedro Springs, Comal Springs, San Marcos Springs, Barton Springs and Salado Springs are found in the fault zone and provide a source of fresh water and an obvious place for human settlement.
References
- ^ Grimshaw, Thomas W.; Charles Woodruff, Jr. (1986). "STRUCTURAL STYLE IN AN EN ECHELON FAULT SYSTEM, BALCONES FAULT ZONE, CENTRAL TEXAS: GEOMORPHOLOGIC AND HYDROLOGIC IMPLICATIONS". The University of Texas. Retrieved on 2008-10-27.
- ^ "DISTURBANCES OF THE STRATA". First Annual Report of the Geological Survey of Texas 134. The University of Texas (1890).
- ^ "Peak Acceleration (%g) with 10% Probability of Exceedance in 50 Years" (GIF). USGS (2002-10). Archived from the original on 2007-06-27.
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- This page was last modified on 27 October 2008, at 00:39.
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