A geological fault line is a fracture or zone of fractures in the Earth’s crust where rock layers on either side have moved relative to one another. Texas contains numerous fault systems within its borders, though the state is situated far from the nearest active tectonic plate boundary. These fractures are remnants of ancient geological forces. While most natural faults in Texas are historically inactive, their presence is a significant factor in current seismic events.
Primary Natural Fault Systems
The state is transected by ancient, deep-seated fault zones that have defined much of its topography and underlying structure. The most prominent of these is the Balcones Fault Zone, a belt of primarily normal faults that stretches for hundreds of miles. This system runs roughly along the Interstate 35 corridor, starting near Del Rio and extending northeastward toward the Dallas area. The surface expression of this fault zone is the Balcones Escarpment, which marks the transition between the Texas Coastal Plain and the higher elevation of the Edwards Plateau. Running parallel to the Balcones system is the Luling-Mexia-Talco Fault System, which shares a similar geological origin and is generally considered stable today.
Current Earthquake Activity and Distribution
Despite the stability of its ancient faults, Texas experiences a low to moderate level of measurable seismic activity. These events are concentrated in specific regions, including West Texas, North Texas, the Panhandle, and parts of the Eagle Ford Shale play in the south. Between 2008 and 2016, the rate of earthquakes of magnitude 3 or greater dramatically increased from approximately two per year to about twelve per year. The West Texas region, encompassing the Permian Basin, has become a major center of activity. The Texas Seismological Network (TexNet) monitors these events, which often occur along pre-existing faults rooted in the Precambrian crystalline basement rock.
The Role of Induced Seismicity
The primary driver behind the significant increase in modern seismic events across Texas is induced seismicity, which refers to earthquakes triggered by human activities. These events are linked to the high-volume injection of produced wastewater deep underground, a common practice associated with oil and gas operations. Injecting this water increases the pore pressure within the rock layers, allowing the pressurized fluid to migrate and reactivate existing faults. In the Fort Worth Basin, intense seismicity between 2012 and 2016 was directly attributed to the injection of flowback water. Researchers have determined that the majority of seismicity near Pecos, Texas, since 2000 is likely induced by wastewater disposal wells injecting at depths greater than 1.5 kilometers.