A magnitude 3.6 earthquake rattled the state at 5:40am CDT on July 17th, approximately 19 kilometers (12 miles) WNW of Caldwell, Kansas and from a depth of 5 kilometers (3.1 miles).
Although no damage was reported, according to the US Geological Survey website’s “Did You Feel It?” feature, the quake was felt as far away as Wichita, located approximately 60 miles to the northeast of the epicenter.
Kansas Quake’s Tectonic Setting
The supposedly-stable continental interior is not a typical location to expect seismic activity, in contrast to areas along plate boundaries or in volcanically active areas.
However, ancient fault systems that have long been buried – and generally deemed inactive – do exist and are quite often the cause of earthquakes in the eastern and central US.
Some earthquakes to occur in Kansas have been associated with certain previously identified geologic features. The Nemaha Ridge, a 300 million year old buried mountain range stretches roughly from Omaha, Nebraska in the north to Oklahoma City, Oklahoma to the south and to the east of this feature lies the Humboldt fault zone.
Lying to the west of these structures is the Midcontinent Rift (also known as the Keewanawan Rift), which formed 1,000 million years ago when the North American continent began (but ultimately failed) to break apart. All of these features have been associated with seismic activity at one time in the state’s history.
Human Induced Seismicity – A More Likely Cause
Although naturally-occurring earthquakes can happen in this region, a more plausible explanation is that this is yet another case of human induced seismicity. Located just north of the state’s border with Oklahoma, the area has recently been plagued by this phenomenon.
Hydrofracturing, or simply known as “fracking,” is the process of injecting chemicals, sand and water into the ground at high pressures in order to fracture underlying rock layers so trapped natural gas can be accessed.
Often the wastewater associated with this process is injected back into the ground for disposal; it is this wastewater injection process that is believed to trigger earthquakes by affecting the pressure on the underlying rocks and fault systems, leading to these sudden subterranean movements.
Kansas Earthquake History
According to the Kansas Geological Survey, between 1867 and 1976 the state experienced at least 25 earthquakes, and between 1977 through 1989, 100 earthquakes were measured.
Since December 2013, five sizable quakes have occurred within 150 kilometers (93 miles) of the epicenter of today’s event, ranging from an M3.9 up to an M4.5.
The largest earthquake ever to strike the state was an M5.1 on April 24, 1867 near Manhattan, Kansas. This quake was felt as far away as Dubuque, Iowa. As Manhattan is located directly on the Nemaha Ridge, and with the Humboldt fault directly to the east of the town, these geologic features were deemed responsible for this historic event.
Seismic Future of Kansas
Although earthquakes are impossible to predict, it is likely this area will see seismic activity as long as fracking in the region continues. This serves as a good reminder illustrating how human actions can affect our planet in previously unforeseen ways and on a very large scale.
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