Earthquakes do much more than literally make the earth quake. The shifting of massive sheets of rock has an effect on all sorts of hydrogeological processes, affecting groundwater and surface water like rivers, lakes, and reservoirs.
Some of this activity, however, is not natural. For example, geologists have extensively documented that when wastewater is injected deep into the Earth, as a means of disposal, it can induce seismic activity, which could, in turn, have hydrogeological effects. As overall induced seismic activity has increased in frequency in recent years, scientists seek to learn more about the secondary and potentially residual impacts of human-induced quakes.
A recent study by Manga et al. is the first documented instance in which an earthquake that was most likely induced by wastewater injection had a visible effect on surface water.
In early September 2016, an earthquake reaching 5.8 moment magnitude (an earthquake rating scale used for the largest quakes) struck Pawnee, Okla., setting a state record. If it is indeed a wastewater-induced quake, it would also be the largest such earthquake on record. The team of researchers concluded that the quake was most likely triggered by one or more of the 26 wastewater disposal wells within a 20-kilometer radius, given that it was a strike-slip event, the type of earthquake most commonly associated with induced quakes in Oklahoma, and had several other telltale physical characteristics.
Several hours into the Pawnee quake, the U.S. Geological Survey stream gauge nearest the epicenter, located at Black Bear Creek, began recording rising water levels. The increase continued for a full week, until heavy rains obscured the data. The pattern of data they were able to collect is reminiscent of water level fluctuations following past earthquakes.
The amount of extra water recorded is just a fraction of the area’s annual water budget and will not affect residents’ water supply, the researchers say. But the Black Bear Creek case is important in that it proves that this method of wastewater disposal has an impact on groundwater systems. Furthermore, if the number of induced earthquakes continues to increase as it has, events like this are likely to become more widespread. To track this progress, the researchers hope to continue to monitor and expand the existing network of stream gauges. (Geophysical Research Letters, doi:10.1002/2016GL071268, 2016)
—Sarah Witman, Freelance Writer