The peaceful and picturesque scenery of southern Brown County was shaken up a bit recently, when a team of researchers led by UW-Green Bay assistant professor of Natural and Applied Sciences John Luczaj called in the heavy equipment for a seismic map of what lies hundreds of feet below the surface.
“It’s an integral part of our understanding of the geology of Brown County,” Luczaj said.
Thanks to a grant from the United States Geological Survey, Luczaj is wrapping up his work mapping the bedrock of Brown County. The project includes exploration of what may be an ancient plate boundary.
“We think that there is an ancient fault zone that runs through here and about 100 feet of vertical displacement has occurred,” Luczaj said. “It’s not an active fault any longer. It’s certainly pre-glacial in age. It’s probably millions of years old or older.”
To investigate, Luczaj moved to shake things up, literally, by bringing in a crew from the Kansas Geological Survey with a heavy-duty “vibra-size” truck. He says this is likely the first seismic investigation of a fault in Wisconsin history.
“They’ve got about a half mile of cable and every eight feet they have sensors called geophones. They’re kind of like big pointy tent stakes that get put in the ground and they have a vertical vibration sensor,” Luczaj described as the crews set up the equipment.
“The unit sends vertical vibrations into the ground that reflect off the rock layers and these things will determine the up and down movement of the ground. By knowing when that happens and which frequencies they use and so on, they can build a picture with computer processing,” he added.
Luczaj says the mapping process is similar to a sonogram. The goal, he says, is to get a clearer picture of the fault that was first discovered 133 years ago by state geologist T.C. Chamberlain, but never mapped.
“What we hope to get at the end of this is kind of like a side view, side picture of what it looks like,” Luczaj said. “So if you had a birthday cake and you cut it in half and you could look at it from the side to see a cross-sectional view, that’s kind of what they’re trying to build. But it’s from a non-invasive process.”
The ancient fault is no earthquake threat but holds scientific and contemporary significance nonetheless. Luczaj says it’s important to build a complete geologic picture of the subsurface because so many people depend on what lies underground.
“There are a number of people who need to know about the subsurface: People who are putting in utilities like water pipelines or gas pipelines, they need to know how deep it is to bedrock. People who are operating quarries, they want to know where resources are. People who are trying to figure our groundwater resources and how groundwater contaminates might move. If you don’t understand the subsurface geology you’re not going to have a handle on what those groundwater characteristics look like, how the groundwater is going to move,” Luczaj said.
This mapping project is one step towards a better understanding of the geologic history of Brown County. For additional background on the two-year project, see our earlier news release.