(Updated Dec. 6, 2011.)
A well-traveled seismometer sits tucked inside a concrete chamber behind the Kent School chapel in Northwest Connecticut, recording earthquakes. The latest event was on Nov. 28 – a minor shake of magnitude 2.0 just north of Medina, N.Y.
Scientists from the Lamont-Doherty Earth Observatory installed the seismograph at Kent in early November – the latest addition to the 40-year-old Lamont-Doherty Cooperative Seismographic Network, which tracks earthquakes around the Northeast. Scores of small earthquakes, mostly unfelt by people, send elastic waves coursing through the ground in the Northeast each year. They’re recorded by more than 40 stations operated by the network, and by other stations that make up a national grid of seismographic sensors.
Now and then comes a larger one – like the 5.8 quake centered in rural Virginia that shook up and down the East Coast. But large or small, they all add to our knowledge of the geology underlying our region, and eventually, perhaps, to a better understanding of the how and why of earthquakes.
Kent came into the network by chance. Several years ago, a station located at the former Camp Columbia in Morris, Conn., had to be shut down after the state bought the land and began turning it into a park. Lamont-Doherty seismologist Won-Young Kim and colleagues were driving around Northwest Connecticut last August, scouting for a good replacement location, when they drove past the Kent School and noticed a tempting outcrop of bedrock.
They drove into the school, mostly deserted during summer break, and checked the library. Math teacher Matthew Austin, assistant director of studies for the school, happened by, and they told him what they were thinking. He directed them to the headmaster, the Rev. Richardson W. Schell, and a deal was struck. The school offered the essentials – a power supply and internet connection, plus a quiet, isolated spot where they could install the seismometer on solid bedrock. In return, teachers and students at the school get to use the seismographic station as a window into the world of geophysics.
“It just dropped into our lap,” Austin said. Teachers will try to integrate the station into the spring geology course, and a monitoring display has been set up in the science building, Austin said.
“One of the things we stress is that science is an activity, and not just a thing you learn,” Austin said. “There’s new stuff being discovered.”
Kim, who heads up the Lamont seismographic network, and his colleagues installed a temporary station at the site, to record whatever ambient vibrations might pop up – such as from a freight train line that runs along the adjacent Housatonic River. The day after they set it up, they recorded the large quake in Virginia. Assured that the instrument’s surroundings were calm enough to allow for accurate and useful recordings, the team moved ahead.
Early in November, Kim, staff associate Mitchell Gold and electronics technician John Contino packed their gear into a white van and drove the winding roads into the Litchfield Hills to Kent. They poured a half ton of concrete for the vault, and set up a global positioning system clock that would keep accurate time to milliseconds for a digital recorder that would receive information from the seismometer .
They returned the next day to install the seismometer. The school and town were without power following the late October snowstorm, so they brought a generator to handle power needs. After lugging several loads of equipment uphill into the woods, they set to work. Contino unbolted the framing for the concrete from the vault. Gold and Kim grabbed a pick and shovel and began hacking out a 60-foot-long trench for the cables, which would run under a leaded glass window into the bell tower next to the school’s St. Joseph’s Chapel. Workmen for the school chipped out a channel for the cables from the mortar between the stones lining the window.
While Gold kept digging, Contino moved inside the tower with his equipment. He set up a makeshift work platform inside the window and began soldering the tiny wires from the internet cable to the connector plug for the digital recorder. Kim aligned the seismometer inside the vault, using a compass, a pair of laser levelers from a hardware store, a slat of scrap wood and duct tape. When he was satisfied with the result, he carefully lowered the seismometer – a 30-pound, 18-inch-tall stainless steel canister about 8 inches in diameter – into the vault and lined it up.
The seismometer has a handle on top, a power cable and a signal cable. Using a small bubble meter on the top, Kim adjusted the canister’s three footings to level it. He loosened three set screws to unlock the masses at the heart of the instrument. Inside are three sensors – each a tiny boom with a magnet suspended between two capacitors. An electric signal keeps the magnet in place. When the earth moves, the instrument measures the amount of voltage needed to keep the magnets suspended exactly in the middle of the two capacitors.
The seismometer can measure ground motion on a scale of nanometers – one billionth of a meter. It’s sensitive enough to record a storm blowing through the woods, or a person walking nearby. The three sensors record a three-dimensional data set that can accurately locate the disturbance and determine its strength.
The seismometer is not a new one: Kim had installed it and several others in Kazakhstan in 1994, as part of the system that had been set up to monitor underground nuclear tests under the 1974 Threshold Test Ban Treaty between the United States and the Soviet Union. When those instruments were replaced in 1999, the older ones were returned to Lamont.
Kim said the Lamont Cooperative Seismographic Network landed $1.25 million this year from the American Recovery and Reinvestment Act (the economic stimulus package passed by Congress) to upgrade the network. Among other things, that allowed them to buy new digitizers, like the one they installed in the bell tower – electronic machines that allow the network to send the seismometers’ signals over the internet. A typical station, like the one at Kent, costs about $30,000 (a good seismometer can cost from $13,000 to $20,000, Kim said).
With Kent finished and online, the seismologists will now start analyzing all the data. You can keep track of the ongoing earthquake monitoring at the network’s website. For the Kent station, go here and select station KSCT.