Waves Rippling Through Groundwater
Earthquakes affect Earth’s intricate plumbing system. The magnitude 9.0 earthquake in Japan on March 11, 2011 affected water levels in groundwater wells in many places in the United States. In this episode of CoreCast USGS Geophysicist Evelyn Roeloffs explains this phenomenon.
Kara Capelli: Welcome to USGS CoreCast. I'm your host, Kara Capelli. Earthquakes near or far can affect you and the water resources you depend on. For example, the magnitude 9.0 earthquake on the coast of Japan on March 11, 2011, affected water levels and groundwater wells monitored by the USGS all over the United States, in places like Oklahoma, Missouri and even as far as Virginia and Florida.
I spoke with Evelyn Roeloffs, a USGS research geophysicist who has studied the effects of earthquakes on groundwater.
Evelyn Roeloffs: Generally, the main way they affect groundwater is that they cause the ground to expand and contract. And the seismic wave that these earthquakes generate actually cause the ground to expand and contract as they pass by. They can travel around the globe a couple of times actually and be recorded on sensitive seismic instruments. So, when those seismic waves pass through, you can see changes in groundwater levels.
Kara Capelli: Scientists and others have been noticing the effects of earthquakes on groundwater for a long time.
Evelyn Roeloffs: I think one of the neatest examples is from back in about 1952, when it was noticed that in a well in a shoe factory in Milwaukee, the water would slosh up and down every so often. And when they put a float recorder on there, and actually made a continuous record of the water level, they recorded things that actually looked like seismograms. And they saw that those variations were actually caused by seismic waves passing the well.
Kara Capelli: The most common effect on groundwater from earthquakes is an instantaneous water level increase or decrease. Recovery to the pre-earthquake level can be so rapid that no change is even detected. I also asked Evelyn about the effects of earthquakes on groundwater quality and quantity.
Evelyn Roeloffs: The spikes themselves, if you actually measure them quickly enough for actual oscillations, where they're making water move in and out of the aquifer and into the well, that can cause the water to become turbid or taste a little bit funny, which doesn't usually last more than a few days, at the most. Occasionally, it will happen that the groundwater level will go down and stay down or go up and stay up but usually not more than a foot or so.
And so, in the short run it might affect the amount of water you can get, depending on exactly where your pump is. But usually, those changes are small compared to the normal changes during the year associated with rainfall and temperature and stuff like that.
Kara Capelli: Though in general, these spikes have very little noticeable effects, sometimes groundwater very near to the epicenter of an earthquake can be permanently affected.
Evelyn Roeloffs: Closer to the earthquake, the effects can be much more severe. And one thing that has happened a couple of times in the U.S. is that the earthquake shaking shakes the hill up and fractures things a little bit and makes it more permeable, so that if people have domestic wells drilled near the top of the hill, they'll find that the water level in those wells may slowly drop. And then, at the same time, the flows in the streams that are draining the hill will increase.
And those kinds of changes really don't recover. They can result in changes of several feet or tens of feet of water. And so, it may cause a well to need to be deepened or even just abandoned. And this happened after the 1989 Loma Prieta earthquake in California near Santa Cruz. And there is also a case of this happening in Pennsylvania a number of years back.
Kara Capelli: The USGS Groundwater Resources Program monitors groundwater across the U.S. through real-time groundwater monitoring. This data can be found at waterdata.usgs.gov/usa/nwis/gw. And don't forget to follow the USGS on Twitter at twitter.com/usgs. I'm Kara Capelli for USGS CoreCast, a product of the US Geological Survey, Department of the Interior.