Earthquakes? In South Dakota?
by Kelly Smith, Meteorologist
November 15, 2011 12:00 PM
When you think of earthquakes one would normally think of places like California but since Sunday night there have been two minor earthquakes right here in South Dakota. Totaling three earthquakes in the last three months.The two most recent quakes were around the same magnitude, the first, which occurred just before midnight on Sunday, and the second, which occurred Tuesday around 2:30 in the morning. Both quakes were centered 183 miles west south west of Pierre; near Ardmore and the Nebraska state line.How common are earthquakes in South Dakota? Earthquakes in South Dakota are not all that uncommon. According to Geologist Tim Cowman of the South Dakota Geological Survey, South Dakota is part of a very old Continental Plate called the Wyoming Craton. The Wyoming Craton is the central core of the North American continental crust today and is a very stable plate when compared to other plates that cause Earthquakes. Stable plates such as the Wyoming Craton occasionally create small earthquakes deep in the earth’s crust that rarely cause damage. While larger earthquakes are possible, they are more unlikely.
(Historical Earthquakes in South Dakota Courtesy: South Dakota Geological Survey)The two more recent earthquakes, which were rated a 3.7 and a 3.4 on the Richter scale are relatively mild. The largest magnitude South Dakota earthquake in the last 100 years was about 10 times more intense, but still a relatively light earthquake at 4.5 magnitude. Geologist Tim Cowman believes that the first more intense earthquake, which occurred on Sunday night, was the main quake and the Tuesday afternoon quake more likely an aftershock. Sunday night’s 3.7 magnitude quake was also larger than a quake experienced earlier this year in Pierre.
Pierre’s August 9th earthquake caused quite a stir in the Capitol city when residents flooded the cities 911 system with calls after feeling the earth move. The quake, which registered a 3.3 magnitude, did not cause any significant damage. No damage has been reported from Sunday or Tuesday’s quakes
. Shaking up the forecast this weekend, is a system that has the opportunity to bring South Dakota our first measurable snowfall event.
(GFS model valid 12z Saturday)A potent low pressure in Colorado will eject out of the rockies Saturday morning giving the potential for some significant precipitation West River early into Saturday.
(GFS model run valid 0z Sunday)The system moves north and east bringing the greatest potential for precipitation in a line from Chamberlain to Marshall, Minnesota although the majority of the state should see at least some sort of precipitation.
(GFS model valid 0z Sunday 850 mb temperatures)Determining whether snow, rain or a mix of both falls will be more difficult. The current models bring extremely cold air on the western side of the low and warmer, moist air on the south eastern side of the low. Final placement of the low will determine where the rain/snow transition line will be. It is highly possible that there will be a large gradient within a small distance making this storm even more difficult to pin point where the snow line will be this far out.Keep in mind that this storm has not formed yet and there WILL be changes in the next couple of days that could change the track and intensity. We will be watching this storm very closely over the next couple of days and bring you updates as this has the potential to be our first snowfall.
**A very special thank you to Geologist Tim Cowman from the South Dakota Geological Survey in Vermillion