Kansas, often perceived as geographically stable, does experience earthquakes. While historically infrequent, the state recorded a significant increase in seismic activity starting around 2013. This modern surge has shifted public and scientific attention to the underlying causes and geographical patterns of these events. The majority of these earthquakes are relatively minor, but the volume of new activity prompted extensive scientific investigation and regulatory action.
Mapping Kansas Earthquake Frequency and Location
The seismic activity in Kansas has historically been low, with only 30 recorded earthquakes between 1981 and 2010. This pattern changed dramatically in the early 2010s, with activity spiking to 127 recorded earthquakes in 2014 alone. The strongest recorded earthquake was an estimated magnitude 5.0 to 5.5 event in 1867, though the largest recent event was a magnitude 4.9 in 2014. Most modern earthquakes fall within the minor to moderate range (magnitude 2.0 to 4.0), which are often felt by residents but rarely cause significant damage.
This modern seismic activity is not distributed evenly across the state. The highest concentration of earthquakes occurs in south-central Kansas, specifically along the border with Oklahoma, in counties such as Harper and Sumner. Activity has also been noted to migrate into central and northern parts of the state, including areas like Sedgwick and Reno counties. These patterns of concentrated and migrating activity have been crucial in determining the source of the quakes.
Understanding Induced Seismicity
The dramatic rise in recent seismic activity is primarily attributed to induced seismicity—earthquakes caused by human industrial activities. The specific activity responsible in Kansas is the deep injection of large volumes of saltwater, a byproduct of oil and gas production, into disposal wells. This wastewater is injected into deep, confined porous rock formations, most notably the Arbuckle Group, which lies just above the crystalline basement rock. Hydraulic fracturing itself is rarely the cause of felt earthquakes, but the subsequent disposal of produced water is strongly correlated with the increase in seismic events.
The mechanism involves the fluid pressure increase within the subsurface rock layers. The volume of injected fluid raises the pore pressure in the Arbuckle formation, which can diffuse downward to ancient faults in the basement rock. This increased fluid pressure decreases the effective stress holding the fault surfaces together, reducing friction. When friction is lowered enough, the natural tectonic stresses present in the crust can cause the faults to slip, resulting in an earthquake.
The Natural Geological Setting
Kansas is situated within the North American Craton, a geologically stable mid-continent area far from tectonic plate boundaries. Despite this setting, the state is underlain by ancient, long-dormant fault systems. The most prominent structure is the Nemaha Ridge, a buried granite mountain range that extends diagonally across the state from Nebraska to Oklahoma.
Associated with the Nemaha Ridge is the Humboldt Fault Zone, linked to historical earthquakes in the region. These faults are typically found within the Precambrian basement rock, which is overlain by a thick layer of younger sedimentary rock. Although these faults are not considered active in the traditional sense, they represent zones of weakness in the crust. They can be reactivated by small changes in stress or fluid pressure, explaining why both natural tectonic adjustments and human-caused fluid injection can trigger seismic events.
Tracking and Responding to Seismic Activity
The Kansas Geological Survey (KGS) tracks and analyzes seismic activity throughout the state. In response to the 2013-2014 surge, the KGS established a permanent, multi-station seismic network in 2016. These sensitive seismometers can detect very small earthquakes, including those below magnitude 1.0, providing detailed data on event locations and depths. This monitoring network replaced a much sparser system and has been instrumental in correlating fluid injection with seismic events.
The regulatory response is managed by the Kansas Corporation Commission (KCC), which oversees oil and gas operations. The KCC implemented actions to mitigate induced seismicity, primarily targeting deep wastewater disposal wells in high-risk areas. These measures include mandatory reductions in injection volumes and limits on injection pressure, particularly in the Arbuckle formation. Regulatory efforts, combined with economic factors, have shown success, as seismic activity declined significantly following the implementation of these policies starting in 2015.