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seismometer

Weisen Shen. Photo by John Griffen/SBU

By Daniel Dunaief

Like so many others during the pandemic, Weisen Shen has had to pivot in his job.

An Assistant Professor in the Department of Geosciences at Stony Brook University, Shen has historically focused his efforts on understanding the geothermal heat flux, or the movement of heat from the core of the Earth, in Antarctica.

Constrained by travel restrictions created by the COVID-19 pandemic, Shen has decided to put his 180 seismometers to good use on Long Island.

“We have seismometers that stay in the basement of our building,” Shen said. “We can’t use them in Antarctica because of the travel ban and other complexities, and we want to make use of them in our community to understand the geology of Long Island.”

Shen is looking for students who might be interested in geology and who might like to plant a seismometer in their backyard, gathering information about how the flow of seismic waves deep beneath their homes and backyards reveals details about the structure, temperature and composition of the land miles below the surface.

Shen, who lives in Syosset, installed a seismometer in his own backyard, which has allowed him to see the signal from the local train station in Sayville. “We seek help from [the local community] to allow us to deploy a seismometer in their back or front yard for a month or so,” Shen said.

Planting a seismometer would involve digging a 15 centimeter by 15 centimeter hole that is 5 inches deep. Shen and his team would cover it. The seismometer wouldn’t need local electricity because it has a lithium battery. 

After about a month, the scientists would dig it out, put dirt back in, and return the backyard to the way it looked prior to taking these measurements.

The machine doesn’t make any noise and does not pick up any sounds from inside people’s homes.

The signal will contribute “to our understanding of the Earth,” Shen explained, including details about the crustal and mantle structure, seismic activities, and the Earth’s vibrations due to civil activities such as the rumbling of trains.

Shen is “more than happy to share data” with the people who host his seismometers. He also expects to produce a research paper based on his studies from Long Island.

He is charging the batteries and testing the instruments and plans to plant them in the field as early as the end of February.

People who would like to participate can reach out to Shen by sending him an email at [email protected] Please include “Volunteer Long Island Imager” in the subject line.

Recent Antarctica Studies

While Shen is focusing his geothermal expertise on Long Island, he hasn’t abandoned or ignored Antarctica, a region he has focused research efforts on because of the vulnerability of the ice sheet amid climate change. He is also interested in the geothermal structure in the area, which reveals information about its geology and tectonics, which remain mysteries residing below the ice. 

Grounded during the pandemic, Shen spent several months gathering and analyzing considerable available data, hoping to understand what happens deep below the frozen surface.

“We are trying to analyze so-called ‘legacy data’ that has been collected over the past two decades,” he said.

On a fundamental level, Shen is trying to quantify how much heat is coming out through the crust, which includes heat coming from the deeper earth in the mantle and the core as well as within the crust.

Traveling beneath the oceans towards the center of the Earth, which would be considerably hotter and more difficult than 19th century author Jules Verne’s fantastic fictional voyages, would expose people to temperatures that increase, on average, about 10 to 30 degrees celsius per kilometer.

Some of the heat comes from the way the planet formed. In addition, unstable isotopes of potassium, uranium and thorium release heat as they decay, which mostly happens within the Earth’s crust. 

In areas with large ice sheets sitting on top of the land, the geothermal heat can melt some of that ice, creating a layer of water that accelerates the ice sheet movement. Indeed, pulling an ice cube across dry ground takes more energy than dragging that same cube across a wet surface.

Moving ice more rapidly towards the periphery will increase melting which, coupled with climate change, could increase the amount of water in Antarctica, particularly in the western region.

Comparing the two ice melting effects, Shen believes global warming, which is more rapid and has shorter term outcomes, plays a more important role in changing the liquid characteristics of Antarctica than geothermal heating, which is longer term.

In collecting available legacy data, Shen analyzed information from the entire western part of Antarctica, as well as parts of the central and eastern regions.

Using a measure of the geothermal heat flux, Shen found some unexpected results, particularly on Thwaites Glacier, beneath which he found a large area with elevated geothermal heat flux. 

Studying geomagnetic data, he compared their results with the results from geomagnetically derived results. In the future, he will combine the two different methods to improve the assessment. 

In a publication last summer in Geophysical Research Letters, Shen presented a new map of the geothermal heat flux for Antarctica with a new resolution of 100 kilometers by 100 kilometers, which is a much higher resolution than earlier studies, which are typically done at 600 kilometer by 600 kilometer ranges.

In West Antarctica, he found a more modest heat flux, despite the area being more tectonically active.

Finally, a major take of the paper, Shen said, is that the Thwaites glacier has a high geothermal heat flux, which could explain why the ice moves more rapidly and readily.

As for his future work, in addition to exploring the seismology of Long Island, Shen said he would pursue his National Science Foundation grant to look for additional water in the boundary between the ice sheet and the mantle.

He is working on “using high frequency seismic records to look for data,” he said.