In a glass cabinet on a second floor corridor of Devlin Hall, outside the offices of the geology and geophysics department, sits a small seismograph that measures the movement of the building—whether caused by gusts of wind, passing trucks, or seismic waves from an earthquake halfway around the world. The seismograph—little more than a weight-and-spring mechanism braced by a few pieces of metal—transmits a recording of the movement to a computer; the resulting seismogram, updated each minute, can be seen on Professor Alan Kafka’s website.

A visit to Devlin Hall on September 10 with Kafka yielded the seismogram pictured above. That morning, at 1:49 a.m. Universal Coordinated Time, a 6.8 magnitude earthquake shook the west coast of Colombia. About seven minutes later the first seismic waves from this earthquake reached Chestnut Hill, showing up as a big, dark peak on the far right of the seismogram (each horizontal line represents one hour). At the epicenter, the earthquake lasted less than 20 seconds; yet the Devlin seismograph recorded shock waves for the next two hours. The higher the magnitude of a quake, the longer the reverberations last. Reverberations from the 9.0 earthquake that caused the tsunami in Sumatra in 2004 were still being recorded in Devlin Hall five hours later. In the lower right corner of the September 10 seismogram, at a little before 13:00 (9:00 a.m. Boston time), appears another distinct pattern of movement, repeated on several lines—this one from packs of students walking past the seismograph on their way to and from classes at the end of each hour. Kafka’s seismograph is for demonstration; a research instrument sits on firmer ground in Devlin’s basement.

The seismogram at left was recorded on the upstairs instrument on August 15–16, 2007, and Kafka calls it “one of the most amazing I’ve seen in my entire career.” In a 17-hour span, six earthquakes were registered—three in Peru, two in Alaska, and one off the Solomon Islands. Two earthquakes a month is more typical.

Katie Bacon is a writer in the Boston area.

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