WHATS IN THIS BLOG:
• Where was the earthquake?
• Were there after-shocks in that area?
• What causes earthquakes in Oklahoma?
• To find out more about fracking and earthquakes.
EARTHQUAKES HAVE BEEN DECLINING IN OKLAHOMA, since the Oklahoma Corporation Commission issued a plan in February 2016 to cut volumes of saltwater disposal by 40% in a large area north-west of Oklahoma City. However, that area did not include the spot just a little east of the north-south line between Stillwater and Ponca City, near Ralston and Pawnee.
This morning, Saturday 3 September 2016, in a small area (but larger than the red dot), an equal largest-ever earthquake of magnitude M = 5.6 occurred at 7:02 am and was followed in the next 3.5 hours by five post-shock tremors of magnitude 3.1 to 3.6.
Here is a quote from one resident of Stillwater:**
Nothing like being shaken so hard you wake up, except it’s the bed and floor that are shaking. Stillwater had a serious earthquake at 7:02 this morning. Sustained ground roll for about a minute or more. Jack said, “Now that’s an earthquake!” And it was. The strongest since we’ve lived here! All seems to be ok, but it was scary to say the least.
WHAT CAUSES EARTHQUAKES IN OKLAHOMA? Oklahoma recorded about 900 quakes in 2015, which compares with about 2 per year in 30 years before 2009. Most scientists agree the earthquakes (at least 90% of them and possibly all of them) are NOT due to fracking, but are due to disposal wells. These are deeper wells which take the produced water (saltwater) from oil and gas wells, about 20% of which is returned frac fluid.
A lot of the salty liquid is injected into the deep Arbuckle limestone formation, which rests on top of the Basement granite. The basement rock has many faults, which can cause earthquakes if they slip (meaning one surface slides across the other surface.) This slip is what causes earthquakes in the San Andreas fault system in California, for example. But in Oklahoma, the fault system was quiescent historically, only 2 quakes per year on average.
That was the situation until the number of disposal wells increased with the revolution of shale gas and shale oil that began in 2003. The revolution was built upon the drilling of long horizontal wells, and fracking them serially with 10 or 20 separate fracs. More wells implies more gas and oil and more saltwater that has to be disposed.
At the bottom of each disposal well a plume of high-pressure saltwater spreads out slowly along the Arbuckle formation, and may eventually contact a fault extending from the Basement rock. The liquid can seep into a fault and cause it to slip, resulting in an earthquake. Some are big faults and cause big earthquakes.
The depth of the big quake this morning was 4.1 miles or about 21,000 ft. The five after-shock quakes were 2.4 – 3.1 miles deep, except for one which was 1.1 miles deep.
TO FIND OUT MORE ABOUT FRACKING AND EARTHQUAKES.
I have written two educational blogs about fracking and earthquakes. Click here for the most recent blog. Then hit back-arrow to return to reading this article.
I have given this year over 15 informative presentations on Fracking and Earthquakes, to groups ranging from 10 to 150. These have been very well-received, partly because I use a lot of props. These presentations are for the layman or the person who has heard about fracking but doesn’t know much about it, although experts will learn something too. The talks are based on data from the field, presented in an entertaining manner.
A brief entertaining video (1 minute) of a part of my presentation can be seen in the YouTube link. Then hit back-arrow to return to this article.
If you know of a group who might be interested in a presentation, please contact me at email@example.com
The Gray Nomad
Probing the practices of Christian faith
** Courtesy of Janyth Pashin.