UK Earthquake Bulletin: Magnitude 5.1 Earthquake Rocks Northwest Oklahoma

The Mw 5.07 Fairview, OK Earthquake & Its Causes

All magnitude 3.0+ earthquake within 16km of 36.477N, 98.718W since the 1st October 2015 - there are 60 in total, 5 of which are magnitude 4.0 or greater

A moment magnitude 5.07 earthquake struck earlier 32km northwest of Fairview in northwestern Oklahoma, at a depth of 8 kilometres. It has been given a maximum intensity of MM7 (damaging) and was felt at least 500 kilometres away in Montana and northern Kansas.

Moment tensor for the Mw 5.07 earthquake at 17:07:05 UTC on the 13th February 2016 (today)

This earthquake is the third largest earthquake to strike Oklahoma in at least the last 50 years (only Prague in 2011 which was M5.7 and an aftershock have been larger). This earthquake's cause is very similar to Prague in 2011, both being caused by an increase in stress in the upper crust caused by gas extraction activities. Though not caused directly by hydraulic fracturing (otherwise known as fracking) which helps to release the gas and oil from the oil shales of Oklahoma and southern Kansas, it is associated with fracking.

Moment tensor for the Mw 4.32 earthquake at 9:45:31 UTC on the 15th November 2015

During fracking water with chemicals is injection down the borehole to aid the process of extracting the gas and oil from the shale. After its use this mixture of chemicals and water is pumped into the pore spaces formerly occupied by the gas and oil within the shale; this process is known as wastewater injection. In the case of this earthquake wastewater injection nearby has been leading to numerous earthquakes greater than magnitude 3.0, with several more than magnitude 4.0.

Moment tensor for the Mw 4.42 earthquake at 4:27:27 UTC on the 7th January 2016

On the 7th January this year a doublet earthquake (Mw 4.42 and Mw 4.80) at 4:27am UTC struck on a southwest-northeast trending left-lateral (dextral) strike-slip fault. In the next 48 hours 11 more event of magnitude 3.5 or larger struck (including a second Mw 4.42 earthquake). Unlike after the Edmond, Oklahoma earthquakes of 29th December 2015, there does not appear to have been media reports of Oklahoma oil regulators stepping in to stop wastewater injection, although I suspect this may well have been the case locally. If they did, the affect of the added wastewater into the shale of this region has still increased the stress below it (an analogy could be progressively putting books onto a bookshelf to the stage where it is creaking, then not putting any more on thereafter). This increased hydrostatic stress has led to today's Mw 5.1 and the Mb 3.9 aftershock.

Moment tensor for the Mw 4.80 earthquake at 4:27:56 UTC on the 7th January 2016

There may well be more earthquakes, although it is likely that today's quake will be the largest. However this large earthquake will have increased stress in the region on its own, adding it to the already increased crustal stresses from the wastewater injection, increasing the chances of another M4.5 or larger event in the next few weeks.