Seismic waves used to 'see' chemical reactions underground, may protect water quality: Study

Researchers managed to see under the surface to assess chemical reactions that alter the quality of groundwater.

A team of researchers led by the Penn State University have found that seismic waves can be used to identify certain chemical reactions that take place under the ground level and help protect the quality of water.

Since these chemical reactions can alter the quality of underground water, 'seeing' under the surface might help protect the essential resource. Susan Brantley, professor of geosciences and director of the Earth and Environmental Systems Institute (EESI) at the university spoke about the research in an article published in Penn State News.

She said that currently they do not know "where the [underground] water is or how it moves in the subsurface because we don’t know what is down there. In this study we used human-generated seismic waves — similar to the waves from earthquakes — to look under the surface".

As per educational website, seismic waves are "energy waves that move through the earth". Scientists use them to study the structure of the interior of the earth by monitoring how the waves "propagate, reflect, and refract".

There are two types of seismic waves present - the body waves and the surface waves. Body waves travel through the interior of the earth while surface waves travel along the surface of the earth.

Seismic activity. Image: Tommy Feldt/Flickr

Seismic activity. Image: Tommy Feldt/Flickr

In the latest study, the team lowered instruments down a 115 foot deep borehole at the Susquehanna Shale Hills Critical Zone Observatory, a forested research site. The logging tool generated and sent out a seismic wave. The researchers then calculated the wave's velocity, how fast it moved as it went away from the tool.

If the velocities recorded were quick, this meant that the wave was moving through "solid bedrock or where pores in weathered rock are filled with water". On the other hand, if slower velocities were recorded, it meant that the waves were going through "weathered rock with air-filled pores, or soil near the surface". The team found that the waves could 'see' where the water had reacted with clay to cause small changes.

They corroborated these findings with data taken from borehole drilling in 2006 and 2013. “These measurements and our ability to combine geochemical and geophysical observations will help us understand the landscape sculpted by water in the rocks beneath us,” Brantley said.

Funded by the US Department of Energy and the National Science Foundation, this study was published in the journal Proceedings of the National Academy of Sciences on 27 July 2020.

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