ABSTRACT

In the early morning of 4 October 2010, a loud noise was heard and shaking was felt in a rural area north of Menominee, Michigan. Within a day, residents discovered what we now identify as a “pop‐up” feature; due to the extensional crack along its crest, it has become known as the Menominee Crack. Within a few days, physical observations were made, and an additional geophysical survey was conducted in 2013 to further investigate the origin of the crack and associated ridge. An autoleveling and seismic refraction survey performed at the site revealed a bedrock layer approximately 2 m underneath the glacial till and also found a significant difference in bedrock velocities observed parallel and perpendicular to the crack. Modeling of a fractured limestone, assuming the seismic raypaths cross fractures in one direction but not in the other, is consistent with these velocities. The origin of the feature remains unknown. Glacial unloading was complete many thousands of years ago, and no significant removal of overburden occurred in recent years, although the occurrence and timing of the removal of a large tree may be more than coincidental.

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