Kansas Geological Survey
Fall 2001
Vol. 7.3

Kansas Earthquakes


While most earthquakes that occur in Kansas are mild, a moderate to large earthquake in east-central Kansas is possible



Kansas Earthquakes–page 1

From the Director–page 2

Erosion Happens–page 3

New Publications–page 3

A Place To Visit–page 4



Now and then, Kansans are reminded that earthquakes don’t always happen somewhere else. Just last July, a minor quake measuring 3.0 on the Richter scale was centered between Augusta and El Dorado in Butler County. Compared to the devastating earthquakes on the west coast of the U.S. and in other parts of the world, Kansas quakes are fairly mild, and most Kansans figure they don’t have anything to worry about. But according to some seismologists, this complacency could be risky.

The July 24th quake in Butler County was just strong enough to be felt. The quake shook computer screens at the city hall in Augusta and rattled several residences in the area, but no damage or injuries were reported.

The Butler County earthquake is associated with a deeply buried feature known as the Nemaha uplift that extends from Omaha, Nebraska, to Oklahoma City, Oklahoma, passing roughly through Manhattan and El Dorado. This uplift formed about 300 million years ago, and the faults associated with it are still slightly active today, especially the Humboldt fault zone that flanks the eastern edge of the uplift. Very little evidence of these faults appears at the surface. Earthquakes associated with the Nemaha uplift are probably a result of minor adjustments in deep-seated rocks.

The largest recorded Kansas earthquake hit the Manhattan area in 1867, toppling chimneys, cracking walls and foundations, and inflicting several minor injuries. The estimated magnitude 5.5 earthquake was felt as far away as Dubuque, Iowa. Since 1867, more than 25 earthquakes with origins in Kansas have been felt; before then, earthquakes generally went unreported.

While most earthquakes that occur in Kansas are mild, a moderate to large earthquake in east-central Kansas is possible. And with critical structures such as major dams and power plants, even a low-probability earthquake has to be taken seriously.

Currently, Tuttle Creek Dam is being studied by seismologists at the U.S. Army Corps of Engineers. The study found that a magnitude 5.7 earthquake, located 12 miles from the dam (at the Humboldt fault), is the smallest earthquake that could potentially cause significant damage. This hypothetical earthquake would probably not cause consequential movement of the dam, but it could damage relief wells that control the flow of water under the dam and lead to dam failure. A seismic event of this nature has a probability of occurrence of about once in 1,800 years.

On the other hand, a magnitude 6.6 earthquake would cause the sand deposits under the dam to liquefy, or turn to quicksand, and lose their ability to support the dam. This, in turn, would allow the base of the dam to spread and the top to drop, and cracking would significantly reduce the ability of the dam to hold water. Although the top of the dam would probably not drop below the lake level, cracking and deformation could allow water to seep through the dam, leading to internal erosion, and eventually, uncontrolled release of the lake. This scenario has a very low probability of occurrence of about once in 10,000 years.

The U.S. Geological Survey’s National Earthquake Information Center maintains a website at http://neic.usgs.gov/neis/. This site has locations and information about recent earthquakes, information about earthquakes in Kansas, and historical earthquake data.

For more information about Kansas earthquakes, see Kansas Earthquakes (KGS Public Information Circular 3), available online at http://www.kgs.ku.edu/Publications/pic3/pic3_1.html. Additional information on the U.S. Army Corps of Engineers’ Tuttle Creek Dam Safety Assurance Program is available at http://www.nwk.usace.army.mil/tcdam/index.htm.

Regional subsurface features associated with earthquakes in east-central Kansas.

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Online February 10, 2003

Comments to: lbrosius@kgs.ku.edu

Kansas Geological Survey