Photo: Arnold Gold / Hearst Connecticut Media
NEW HAVEN >> Fifteen seismographs placed in forests, farms and backyards across northern Connecticut picked up the vibrations of a 7.9-magnitude earthquake in Papua New Guinea on Jan. 22.
That information arrived from 200 kilometers — 124 miles — under the Earth’s surface, deep within the planet’s upper mantle, below its crust. It will help geologists at Yale University and elsewhere better understand what lies underneath Connecticut. It will also help explain why the supercontinent Pangea split about 200 million years ago, forming the Atlantic Ocean and creating the continents of North American, South America and Africa.
The data might also help explain why “the Atlantic basin is opening and getting bigger and the Pacific Ocean basin is getting smaller” and why the continents rimming the Pacific are likely to bash into each other and form a new supercontinent hundreds of millions of years from now, according to Maureen Long, a Yale professor of geology and geophysics who is overseeing the Seismic Experiment for Imaging Structure beneath Connecticut, or SEISConn.
That opening and closing of the ocean basins is known as the Wilson cycle.
Listening to Earth
The 15th station was installed about a month ago and started recording data, and now Long and John Aragon, a 2017 Yale graduate and SEISConn project manager, can focus on analyzing the information recorded on the seismographs and start “turning those wiggles into insight [about] how the Earth works beneath Connecticut,” Long said.
“We want to know what’s down there now, what does the structure of the crust and mantle look like beneath Connecticut today and then what does it tell us about how these plate tectonic processes have operated in the past,” Long said.
“The Earth is sending signals all the time with big earthquakes, but you need the instruments to receive the signals that are going on naturally,” said Aragon, who also goes by Juan. Long compared the process to a CT scan of the body; the vibrations deep within the Earth are like the radiation that maps the body’s internal organs.
The seismographs are “just like shining a little flashlight down” into the Earth, Aragon said. It’s a flashlight with a long beam. He compared the depth at which the seismographs can register vibrations to the Kola Superdeep Borehole in Russia, which at 12.26 kilometers (7.6 miles) is the deepest point on the Earth.
“We can pick up waves in many cases that have passed through the Earth’s core,” Long said. While most waves the seismographs pick up are from earthquakes, Long said, “I do expect that we probably recorded the North Korean nuclear test.”
The breakup of Pangea was “a really important process in plate tectonic theory,” Long said, but geologists don’t have a good understanding of how the Earth’s plates move, creating earthquakes along the fault lines between them.
“We really don’t understand very well exactly how this process works,” Long said. “It’s a pretty fundamentally unsolved problem in plate tectonics. … What makes a supercontinent break up? Presumably something is happening in the deep Earth to generate the forces that would rip apart a continent.”
When thinking about earthquakes, Connecticut does not spring immediately to mind, but, Long said, “Connecticut has amazing geology. Up in the northwest part of the state, these rocks are about a billion years old. In the southeast part of the state is another chunk of pretty old rock,” about 700 million years old, she said. “This is a bit of continent that was probably formed either as part of Africa or just short of offshore of it. All these pieces of the Earth’s crust kind of got glommed onto North America,” like “a 10-car pileup,” she said.
About 300 million years ago, when the Appalachian Mountains were formed, that southeastern part of the state “got slammed into what is now Connecticut and when Pangea broke up it basically got left behind.”
“Connecticut has just this super-complicated and rich geologic and tectonic history,” Long said. What makes Connecticut especially interesting is its central spine, called the Hartford Rift Basin. “These are basically volcanic rocks that were formed 200 million years ago as Pangea was breaking apart,” Long said. The aftereffects can be seen as West Rock and East Rock in New Haven, Sleeping Giant in Hamden and the Hanging Hills in Meriden.
“This is a region where the supercontinent started to break apart and then it failed and then instead the supercontinent broke apart somewhere to the east,” Long said. The Hartford basin is “almost like a snapshot of that rifting process,” she said. “Beneath the Hartford basin is a perfect opportunity to study that process,” which she said is vital to plate tectonic theory.
The Hartford Rift Basin is “frozen in time,” Aragon said. “It’s a rift basin that failed so it’s sort of frozen in that immature state.”
Aragon noted that evidence of the Earth’s tectonic plates can be seen from space or even on the Google Earth website, “but it doesn’t tell you what’s happening in the Earth’s mantle,” which is the layer below the crust, he said.
Change takes time
The movement of the vast tectonic plates is an exceedingly slow but dynamic process. “Pangea is the most recent supercontinent, but if you go back even further into Earth’s geologic history there is increasing good evidence that’s there have been several older supercontinents,” Long said. A billion years ago, there was a supercontinent known as Rodinia. Now, “the Atlantic basin is opening and getting bigger and the Pacific Ocean basin is getting smaller,” she said.
But a new supercontinent won’t form for “hundreds of millions of years into the future,” she said.
The 15 stations are installed in a line across northern Connecticut, where there is less surface noise, from the YMCA in the Lakeville section of Salisbury to one in Rhode Island at the Chepachet Farms and Carriage Works. There’s one in the Yale Camp in the Great Mountain Forest in Canaan’s Falls Village — the camp is maintained by the Yale School of Forestry and Environmental Studies — another in Winsted and one in the Yale Myers Forest in Eastford.
“Sometimes we just knock on doors to find places to stick these things,” Aragon said.
The stations, which consist of a seismometer buried in a 33-gallon drum, powered by solar panels, will collect data for two years. “We do expect to have some preliminary measurements and conclusions within the next six months or so, so in that sense it’s kind of an exciting time in the project,” Long said. The data will be stored on memory cards, which will have to be collected about every six months. Despite its high-tech aspect, the project is “off the grid.”
Thirteen high school teachers have helped set up the stations through the weeklong Field Experiences for Science Teachers program, Long said. They helped dig the holes, pour concrete and set up the solar arrays, as well as collect initial data. They also jumped up and down near the seismographs to assure they were working properly.
Megan Weingart, who teaches Earth science and related subjects at Cheshire High School, was one of those who appreciated “the experience of actually doing science again. … These seismographs are just so sensitive that they are able to pick up the [ocean] waves hitting the continent,” which come through as background noise, she said.
Weingart has had Long speak to her class and has told them of her own experience, but is looking forward to be able to use the collected data in her teaching. “Just knowing in general what’s directly below the crust of the Earth in Connecticut, it brings it home to the students and makes it more pertinent and interesting,” Weingart said.
“Until now, seismologists have not collected a data set that is this detailed or that will allow us to do detailed imagery beneath Connecticut,” Long said. “This is going to be a pretty big leap forward to understand the deep parts of the crust and mantle of where we live.”
Call Ed Stannard at 203-680-9382.