The average student walking around the Tufts Art Gallery parking lot, just behind Jackson Gym, may never guess that they are passing over a fault line that runs under the campus. Students may notice an outcropping of rust-colored rock, marked by an unassuming silver sign that reads, “Tufts Quartzite.” This exposed rock is tilted to the north. To those in the know, this seemingly innocuous detail is one of the first indications of something unusual beneath the surface. According to Professor Anne Gardulski of the Tufts Department of Earth and Ocean Sciences, “This is just opposite of the tilt of rocks—to the south—that were exposed when the Campus Center was built, which is just a short distance away to the north. We speculated that the rocks might be literally folded or bent, but also noted that the rocks exposed behind Jackson are very fractured, broken, and iron-stained.”
While this rock was abnormal, Professor Gardulski, whose work focuses on sedimentology and stratigraphy, didn’t focus on it until the department began drilling holes at different sites on campus in 2009, revealing the presence of the fault line. However, the “real research” began in 2012 when the first two of the three holes were drilled in the parking lot behind Jackson.
This type of geological research involves studying the rock cores and drill cuttings obtained after drilling holes. Professors and students alike formulate descriptions of rock types, fractures, and evidence of faulting. Following this empirical analysis, an outside company creates “thin sections,” or microscope slides containing tiny portions of the rocks. These “thin sections” allow researchers to view individual minerals as well as their arrangements and textures. Finally, another outside company creates a video log of each hole. From this footage, researchers can glean more information about faults within the holes.
“As I studied the cores and drill cuttings [from around Tufts campus], I realized that, indeed, we seemed to have drilled through a fault as well as a fold,” Gardulski explained. “The structure is really quite complex. Although more work needs to be done on the problem, it appears that this ‘fault’ is actually a fault zone, with a number of strands of the fault concentrated in the area just south of the Jackson Gym. We formally call it the Jackson Fault or Tufts Fault.”
Gardulski believes that the fault behind Jackson Gym is likely a reverse fault—rock from the upper side of the earth moves either downwards or upwards relative to the lower block due to tensional or compressive forces. While the term “fault line” can seem alarming and foreboding, this kind of fault is very common and does not pose an immediate or serious threat to the Tufts campus. In fact, the Earth’s crust is covered with fractures, like the Jackson Fault, which have seen little motion, though are more likely to experience disturbance than an unbroken surface area.
Now that we know about the existence of a fault line beneath Tufts, professors and students are beginning research on the orientation of the fault line, as well the formation of the fault line. Researchers will use the video logs and bore holes around campus to “estimate how much offset there is across the fault plane.” Professor Gardulski believes the fault line is running east-west, but needs to study the video logs and holes in greater detail before making a conclusion.
“Finally, we need to figure out if the fault formed under compression or tension on the Earth’s crust. This will be harder to determine, but I think we can do it by very detailed study of the microstructures in conjunction with analysis of the fractures identified in the geophysical logs,” she said.
The Jackson Fault places the Tufts campus in a unique historical location. Studying the fault lines of eastern Massachusetts, including the one beneath Tufts, according to Gardulski, helps piece together the geologic history of New England.
“Part of the reason for studying the faults and the rocks they affect is to understand the geologic history of New England…it helps us understand the ‘jigsaw puzzle of rock’ under the campus. Our geologic history on the Tufts campus is a piece of the larger history of our continent and the world,” she explained.
“I would not be very concerned that we could experience earthquakes caused by movements on these faults—they are ancient, probably at least 150 million years old, and probably have not had any significant motion on them for nearly that long,,” Gardulski said.
Gardulski suggests that, though the Jackson Fault can support structures above it, campus building projects should consider the weakness of the rock in fault zones.
“The possibility of shattered rock in a fault zone means that fluids more easily move through, altering and weakening the rock,” she said. “That does not mean a building should not be built on one of these ancient faults, it just means that the engineering of the foundation should account for the broken rock.”
The city of Boston has begun to do just this—a Boston Globe article from 2012 describes changes, implemented preventatively, to building codes in towns around the city. The new building code requires the renovation and reinforcement of “critical buildings,” meaning fire stations, police stations, and emergency shelters. This code differs from the code adopted in 2010, the International Building Code, based on California’s own code, in that it calls for even “minor renovations” including the addition and elimination of doors. Citizens from fire chiefs to engineers overwhelmingly felt that the code was too financially demanding for a state that hasn’t experienced major earthquake since 1755, between 6 and 6.5 magnitude, according to Gardulski.
“Thankfully, earthquakes are no more likely in the Tufts area than anywhere else in Massachusetts. There are actually much larger, ancient faults a bit further west of the Boston area, but very little motion has occurred on them for hundreds of millions of years!” explained Gardulski.