Wednesday 8 December 2021

Magnitude 4.3 Earthquake in central Kansas.

The United States Geological Survey recorded a Magnitude 4.3 Earthquake at a depth of 3.0 km, about 5 km to the southwest of the city of Gypsum in Saline County in central Kansas, at about 7.45 am local time (about 1.45pm GMT) on Wednesday 8 December 2021. There are no reports of any damage or casualties associated with this event, but it was felt across much of Kansas, as well as southern Nebraska, western Missouri, and northern Oklahoma.

The approximate location of the 8 December 2021 Saline County Earthquake. Google Maps.

Earthquakes on southern Kansas are rare, and their causes poorly understood. There are two fault zones in the south of the state, The Humbolt Fault to the southeast of Wichita and the Crooked Creek Fault to the southwest of Dodge, though both of these are ancient structures not considered to be particularly active, and both lie a long way from this event. 
Small Earthquakes have also been attributed widely to the activities of hydrocarbons companies, notably the extraction of oil and gas, which is a major industry in Kansas, but not in the area affected by this quake. In particular the process of hydraulic fracturing, or fracking, in which water, sand and chemicals are forced into buried sediments at considerable pressure in order to shock them into releasing trapped hydrocarbons, is often linked to Earthquakes, but this is restricted to the east of Kansas. The practice of storing hydrocarbons in underground salt deposits that have previously been worked commercially has also been linked to seismic events, as it causes repeated inflation and deflation of the affected beds, which can trigger previously quiet and unnoticed faults.  

Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the USGS here.
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