A group of students from Georgia Tech, led by Professor Zhigang Peng, conducted a refraction survey at Lilburn, Georgia, in March 2015, as part of their exploration seismology course project. The site is on the property that hosted an Earthscope Station TA.Y52A (now part of the Central and Eastern United States Network, http://ds.iris.edu/mda/N4/Y52A, last accessed October 2015). During their first visit, the host, Ms. Sheryl Hartman, mentioned that on 15 August 2014, their family friend Dan Carey found a cannonball-like object in their backyard while they were enjoying a picnic (Fig. 1). They called the Gwinnett Police immediately,...

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