Sparta NC Earthquake Could Impact Your Well

The August 9th, 2020 M 5.1 earthquake near Sparta, North Carolina, occurred at 8:07 am. This earthquake occurred in the interior of the North American plate. Such mid-plate earthquakes are known as intraplate earthquakes and are generally less common than interplate earthquakes that happen near tectonic plate boundaries. This earthquake was preceded by at least four small foreshocks ranging from M 2.1-2.6, beginning about 25 hours prior to the mainshock.

Large earthquakes are relatively uncommon in this region. Moderately damaging earthquakes strike the inland Carolinas every few decades, and smaller earthquakes are felt once every year or two. In the 20th century, one earthquake M5 and larger occurred within 100 km to this August 9th events, a M5.2 in the Great Smoky Mountains in 1916. The largest recent earthquake to impact the east coast was the M5.8 Mineral Virginia earthquake on August 23rd, 2011, roughly 300 km to the northeast of this August 9th earthquake. The Sparta earthquake was not as widely felt.

Private wells can be impacted by earthquakes. The most common type of observed ground-water response is an instantaneous water-level fall or rise and can occur near or far from the epicenter of the quake without significant change to the rock formation. Recovery to the pre-earthquake water level can be so rapid as to be almost unnoticeable, or it may take as long as several days or months. Water level changes can be large enough to make a well flow to the land surface, or render a well dry.

Well water can also become cloudy or take on a different color, smell and feel. The water can become contaminated with dirt, minerals and other solids, as well as bacteria due to damage to the casing and grouting. To see if your well has been impacted, you will have to empty your pressure tank and see what pumps out of the well. Turbidity could move through the system and pass in a short period or not depending on the specific geology, soil type and hydro geology. However, if there are any indications of impact the water should be tested to ensure it is still potable.

In 1998 there was an earthquake in northwestern Pennsylvania that caused about 120 local household drinking water wells to go dry within 3 months after the earthquake, they never recovered. Very large earthquakes even at great distances can also cause the water table to temporarily rise and fall when the seismic long waves pass through the state and this is the most common type of groundwater response. The USGS documented a 2-foot water-level rise in a well in Wisconsin, in 2002 after an earthquake in Alaska more than a thousand miles away.